It’s been over 20 years since astronomers first discovered that the expansion of the Universe is accelerating thanks to dark energy. And in these decades, astronomers still don’t have much evidence for what could be causing the increased expansion rate. Maybe there’s something else going on to explain it.

Show Notes | Transcript

Escape Velocity Space News (CosmoQuest)

PODCAST: Ep. 4: The Search for Dark Matter (Astronomy Cast)

PODCAST: Ep. 11: A Universe of Dark Energy (Astronomy Cast)

The Dark Energy Survey

The Nancy Grace Roman Space Telescope (NASA JPL)

South Pole Telescope (University of Chicago)

Physical Review Letters (APS)

Hot new early dark energy: Towards a unified dark sector of neutrinos, dark energy and dark matter (Physics Letters B)

Casimir Self-Interaction Energy Density of Quantum Electrodynamic Fields (Physical Review Letters)

Dark matter (CERN)

Dark Energy (Hubblesite)

Doppler Shift (Swinburne University)

Equation of state (cosmology) (Wikipedia)

Hubble’s Exciting Universe: Measuring the Universe’s Expansion Rate (Hubblesite)

Planck (ESA)

WMAP- Content of the Universe (NASA)

Supernovae Were Discovered in all These Galaxies (Universe Today)

What are Cepheid Variables? (Universe Today)

Carnegie Supernova Project II: The Slowest Rising Type Ia Supernova LSQ14fmg and Clues to the Origin of Super-Chandrasekhar/03fg-like Events (The Astrophysical Journal)

Research team discovers unique supernova explosion (Phys.org)

Planck and the cosmic microwave background (ESA)

Hydrogen Epoch of Reionization Array (HERA)

FOLLOW-UP: What is the ‘zero-point energy’ (or ‘vacuum energy’) in quantum physics? Is it really possible that we could harness this energy? (Scientific American)

First principle (Wikipedia)

WMAP Inflation Theory (NASA)

Could a Dark Energy Phase Change Relieve the Hubble Tension? (Universe Today)

Michael S. Turner (University of Chicago)

What is the Casimir effect? (Scientific American)

The Nobel Prize

The Higgs boson (CERN)

Particle Fever (2013) (IMdB)

Back to Top

Transcriptions provided by GMR Transcription Services

Fraser Cain:                 Astronomy Cast Episode 669, Challenges to Dark Energy. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, the publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?

Dr. Pamela Gay:         I am doing well. The third episode of our new TV show aired Saturday and we got it to the station 90 minutes before it was due, due to computer crashes, because computers know.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         But if you haven’t checked it out yet, it’s Escape Velocity Space News. It airs on Now Media and I am gonna be putting together a podcast version and loading that up later today.

Fraser Cain:                 Congratulations, that’s amazing. It’s been over 20 years since astronomers first discovered that the expansion of the universe is accelerating thanks to dark energy. And in these decades, astronomers still don’t have much evidence for what could be causing the increased expansion rate. Maybe there’s something else going on to explain it.

                                    If you go back into the archive of Astronomy Cast shows, one of the first episodes that we did was Dark Matter and then after that was Dark Energy, like within the teens anyway and we’ve brought it up a couple of times since them, but I had been expecting in the 15 years that we’ve been doing this show that we would have something more to say on the matter. But to be honest, not much has been figured out, apart from some really interesting new surveys, like the Dark Energy Survey Telescope, the development and eventual launch of the Nancy Grace Roman Telescope. We still have no idea what this is.

Dr. Pamela Gay:         One of the things that actually caught me by surprise is I was expecting to spend today talking about the new results from the Dark Energy Survey and the South Pole Telescope, and there are actually two really cool papers that have both come out in Phys Rev Letters in the past couple of months that are both clearly the, hi, we’re theorists, we have predictions, there are only two of us on this paper, please give us the Nobel Prize when our predictions prove true.

Fraser Cain:                 Right.

Dr. Pamela Gay:         And so, we may be getting to the point that theorists are starting to figure out how to get a handle on things, and they’re finding answers that may also help confine dark matter, which is kinda cool.

Fraser Cain:                 Well, that’s great. So, then, I guess, what is the evidence for dark energy?

Dr. Pamela Gay:         Basically it comes down to when you measure the distance to a supernova and you measure the rate at which that galaxy is moving away from us using doppler shifts. We find that the universe is actually accelerating over time, which is not something that was in anyone’s predictions but it was in the math in the form of a constant to the equations of state for the universe. When Einstein originally came up with these equations there was an integration factor, when you integrate you have to add a constant, and he assumed that the constant would have a value that caused the universe to be static.

A few years later, Hubble came along, found the universe is expanding. Now we have a constant that makes sense for that. But it turns out that if you have a universe that is accelerating apart, that is a value for the equations of state, and so now what we’re finding is, in order to explain the geometry of our universe, which is flat, flat, flat, very flat, and an accelerating universe, you have to have 70% of the universe made of something that isn’t observable matter, that’s about 4-1/2 percent of the universe, that isn’t dark matter that gets observed through gravitational lensing, gets observed through rotation curves of galaxies, gets observed through the motions of galaxies and clusters, that’s 27-ish percent and instead you have dark energy.

Fraser Cain:                 So, this measurement really relies on how good the measurements to those type 1A supernovae are.

Dr. Pamela Gay:         Yes. And it also comes down to, once we realized, okay, so we have from the Planck Observatory the flat geometry and then you combine it with everything else and you look at the mass density of the universe, the only way to explain the mass density of the universe is to have this extra stuff as well. So, you can get to dark energy from a couple of different ways but to get at the value that we’re seeing, yes, that came very clearly from the 1998 observations that the universe is accelerating with time and its expansion.

Fraser Cain:                 And we did some coverage on a new database that came out a couple of months ago, where astronomers had gone through and like recalibrated, normalized all the data for about 1,000 total type 1A supernova measurements and if anything, have gotten even more accurate.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 You overlap the Cepheid variables with type 1A supernovae, the distance ladder is beautiful, the error bars are ever shrinking and the amount of dark energy in the universe is zeroing in on this. They’re really nailing this number.

Dr. Pamela Gay:         And one of the wild things about this is we keep trying to find an excuse that maybe further back in the universe these kinds of supernovas, due to the change in the chemistry, would have different properties, and we do keep observationally finding random exceptions. There was a super cool type 1A supernova that went off while inside of another star, which is one way to blow up a white dwarf.

Fraser Cain:                 You can imagine that would pollute the results a little bit.

Dr. Pamela Gay:         Right. But these one-offs that we’re finding are super cool but they are one-offs. The vast majority of the type 1A supernovae are just boring white dwarfs that ate more than they could hold without changing states.

Fraser Cain:                 Right. And so I guess one possibility is that the type 1A supernovae aren’t the standard candles that astronomers had always believed but the evidence is continuing to build that yes, indeed, they are.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 Except for these ones where one star blows up from inside another star.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 Right.

Dr. Pamela Gay:         And so, I mean it’s just like saying most human adults are between five foot and six foot, yes, there are people who are only three foot and there are people who are only seven foot, but the vast majority of us are between five and six foot. So, yeah, it’s averages.

Fraser Cain:                 So, then, let’s talk about some of the largescale surveys that have been developed to try to get to the heart of dark energy. Not necessarily explain it, I guess, but at least to confirm it, map it, try and nail down its parameters.

Dr. Pamela Gay:         So, the big one with the obvious name is the Dark Energy Survey, which was done from down in Chile where they observed with extreme sensitivity vast swaths of the sky with the goal of looking to see how the structure of the universe evolved with time. So, the idea here is, we know that the universe started out as pretty much smooth distribution of particles. It wasn’t even anything more fancy than particles initially, with slight over and under densities that were created by soundwaves moving through the early universe.

                                    That mostly smooth distribution that we can measure in the cosmic microwave background, then had to collapse down into galaxies, stars at the smallest scales, but then clusters of galaxies, walls of galaxies, super clusters at the largest scale and it does that over time. And we have models that basically say okay, here is the CMB, here is the modern universe, let’s fill in in between and the Dark Energy Survey was designed to get at the more recent few billion years.

                                    The next survey that is super exciting to look at is HERA, which is being done in the radio, looking at the redshifted 20-centimeter line of cold hydrogen, that the detectors for this, they’re looking at wavelengths of light that instead of being just 20 centimeters are instead many, many feet, so, longer than us. And in these longer wavelengths we are able to start seeing how cold hydrogen was distributed in the early universe, start piecing together how cold gas clumped and then got re-ionized in the era of re-ionization.

                                    And between these different surveys, we’re working our way through measuring what was the structure over time so that we can better confine our models and say, okay, was the amount of dark energy constant over time. Was there some sort of a phase transition? Was there a kick somewhere? And these are the kinds of questions that folks are trying to answer, is what observables can dark energy give us that will help us confine our theories?

Fraser Cain:                 And so, in addition to the type 1A supernovae measurements, they’re able to now look at these galaxy clusters and then on top of that they’re looking at the concentrations of these regions of hydrogen gas. And so, you’ve got like three independent lines of observation that theoretically should allow you to map out the amount of dark energy.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 And is the assumption that they’re gonna find it? Like I know the Dark Energy Survey is still partway through its survey. You didn’t even mention the Nancy Grace Roman, it’s gonna be launching in 2025, and –.

Dr. Pamela Gay:         Well, you don’t count your satellites until they’re orbiting.

Fraser Cain:                 Fine, fine, okay. Pamela, put your hands over your ears. Audience, the Nancy Grace Roman, one of its main jobs is going to be to characterize dark energy, doing kinda the same thing that the Dark Energy Survey is but from space. So, this is classic, right. Like if you don’t have an easy answer then you build more instruments, more observatories. You keep trying to characterize the nature of the problem, building hypotheses, testing them against your observations, removing bad ideas one after the other and hopefully trying to pin down the final thing. So, we may never know what’s causing dark energy but we’ll have it measured to Six Sigma accuracy.

Dr. Pamela Gay:         Well, and the other side of it is the particle physics side. So, we know that dark energy, whether it’s a force, an energy, a field theory, whatever it is, puts into every cubic meter of space basically a proton-ish worth of energy. And so, how do you explain that energy existing? And by better understanding the quantum mechanic side of the universe, the particle physics, the vacuum energy, are sterile neutrinos actually a thing or not, this is another way of coming at the fullness of the universe by looking at the smallest factors inside of it.

Fraser Cain:                 All right. So, I guess, you found a few papers that have been proposing some alternative explanations that would explain the observations but not necessarily be new energy that’s being injected into every cubic meter of the universe, which I guess sounds satisfying. Like the fact that energy is appearing out of nowhere, that’s unnerving, so what are they proposing?

Dr. Pamela Gay:         So, the first paper in here, I have to look at my notes, the first paper came out from Martin Sloth and Florian Niedermann, where they’re looking at new early dark energy. And the idea here is our universe has undergone phased transitions in terms of the energy of the entire universe. So, the first massive phased change occurred in the first fractions of a second, where we essentially went from every basically molecule sized bit of the universe expanding out via inflation, which we also don’t know what is, to be about the size of the observable universe according to some ways of looking at it.

                                    And this massive, fairly instantaneous epic of inflation may have only been one of two phased transitions or there could have been a later phased transition that, if there testable ideas are right, leads through first principles to having a cosmological constant of 72, which is within error bars of what we see for the modern universe, and fixes the discrepancy we see with the old universe.

Fraser Cain:                 And so, sorry, so like, the idea of inflation –.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 Happening in just the first fraction of the Big Bang was developed I think back in the ’70s –.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 To help explain a lot of the problems with the Big Bang. Like the Big Bang beautifully explains the universe as we see it today, but there are these flaws in the theory. How can vastly separated parts of the universe be similar temperature, there’s a bunch of these ideas. And so, one of the theories is that, in fact, there was this period of rapid inflation that carried everything away from each other really quickly and then it settled down.

                                    So, I think baked into modern cosmology is already this idea, as you say a phased changed, a dramatic change in the expansion rate of the universe. So, it doesn’t seem that surprising that there could then have been others later on.

Dr. Pamela Gay:         Right.

Fraser Cain:                 So, when would have this other, they’re calling it, what, early, what are they calling it, early –?

Dr. Pamela Gay:         They’re calling it new, early dark energy.

Fraser Cain:                 Dark energy. Right, okay.

Dr. Pamela Gay:         So, NEDE is the abbreviation.

Fraser Cain:                 New early dark energy, right. And so when would this have occurred in the timeline of the universe?

Dr. Pamela Gay:         This still would have occurred during what they refer to as the dark times prior to the release of the cosmic microwave background. And it fits in with the way – Michael Turner, who is a prominent cosmologist, now professor emeritus from the University of Chicago, he says there’s basically these three unknown pillars of cosmology, inflation, dark energy which he actually named, dark matter. And so, this looks at that early period, makes some solid predictions for temperature details that we should be able to see with enhanced continuing to look at the cosmic microwave background, which tells us everything apparently.

                                    But it also makes some finite predictions for what kinds of neutrinos should be out there, and what kinds of specific particles we can expect to find, thus, also perhaps explaining dark matter. So, we have one coherent theory spelled out in a letter-sized research article making concrete predictions. It seems good and just needs tested now but it’s not the only one out there.

Fraser Cain:                 All right. Well, let’s talk about the other one, then.

Dr. Pamela Gay:         So, the other one is by Alexander, and I’m going to mispronounce this and I am sorry, this appears to be a Ukrainian last name, Tkatchenko, and the other one is Dmitry Federov. And they look at the vacuum energy of the universe, and vacuum energy is something we know is real because of the Casimir effect, which is just one of the best named effects in particle physics. The dude’s name was Casimir but it just sounds cool to say.

                                    And what the Casimir effect says is if you take two plates that are capable of conducting electrons and you put them extremely close together but you’re not actually running charge through them and they’re not being exposed to any fields, nothing should happen I a vacuum. But the reality is, if you put these two plates just a couple nanometers apart within a vacuum, they will either attract or repel due to the constant creation and destruction of virtual particles that are in their creation and destruction, creating a field. So, if you have a proton spring into existence as a virtual particle between these two plates, that proton has a field and it creates the effect.

Fraser Cain:                 Right.

Dr. Pamela Gay:         And we see this.

Fraser Cain:                 Right. And if I understand, like the Casimir effect, because the gap is so small the virtual particles of only certain sizes can pop into existence outside or as a field.

Dr. Pamela Gay:         Right.

Fraser Cain:                 Outside the plates and then they are pushing inward, there is essentially a field on the outside and not so much field on the inside and it’s pushing on these plates. And once you move the plates farther and farther apart, now there’s room for the fields to appear both in between the plates and outside the plates.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 And then that force goes away. And it sort of shows you the presence of this vacuum energy that is everywhere. And it’s been beautifully measured, so no one argues with the existence of vacuum energy. The assumption, though, is that this energy cancels out, goes away very quickly and doesn’t provide any ongoing force to the universe.

Dr. Pamela Gay:         And that’s one school of thought. Another school of thought is, no, it’s totally providing dark energy-like forces, but when they do all the maths, they have consistently come up with an amount that is too large by a factor of 10 to the 120 for the theories that I like the best and that are among the prominent theories. And the best case for getting it down has, until this paper as far as I know, been 10 to the 30th. And when you’re off by somewhere between 10 to the 30 and 10 to the 120, it really doesn’t matter.

Fraser Cain:                 That’s a lot. Yeah.

Dr. Pamela Gay:         It’s a lot. And this is where these two researchers, Tkatchenko and Fedorov, they said, well, okay, what if the vacuum energy has a polarizability, that the particles can actually have alignments that affect what can and can’t come into existence and annihilate. And they make again solid predictions that should be testable if we go looking with new technology that we don’t currently have laying around.

And it’s just one of those nice, simple, elegant ideas of we know stuff can be polarized. We know particles can be aligned. What if just the universe as a whole has this polarizability characteristic to it that we just hadn’t been including? And again, with this research, it makes set predictions on what to go look for. It looks at the particles that are out there and says, okay, here is what to see in particular physics and I don’t know which team I’m rooting for more. I like the polarizability one.

Fraser Cain:                 Why choose?

Dr. Pamela Gay:         Well, I mean that’s – it’s two theory papers making predictions. Both of them have only two authors. Both papers are clearly gearing up for a Nobel Prize. It’s always good to cheer for people but I guess I’ll cheer for both.

Fraser Cain:                 Yeah. When you think about the winning Nobel Prizes, many of them start this way.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 That a theorist puts together a paper and says there should be a particle called the Higgs boson, right, and then 30 years later experimenters are finally able to find it, and this is the same thing. So, I mean I guess if dark energy makes you uncomfortable already –.

Dr. Pamela Gay:         This doesn’t help.

Fraser Cain:                 Buckle up. Yeah.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 You still got another 30 to 50 years of searching and scanning and trying theories to try and narrow in on an answer to it.

Dr. Pamela Gay:         And if you want to get a feel for what it’s like within the field of particle physics to watch people so clearly chasing Nobel Prizes, watch the moving Particle Fever, it is very delightful. It shows the good, the bad and the ugly of scientists being scientists, and just the joy that comes from people getting to see their dreams come true through instrumentation.

Fraser Cain:                 I will check that out.

Dr. Pamela Gay:         It’s really cool.

Fraser Cain:                 Yeah, that’s awesome. All right. Well, thanks, Pamela. I hope within the lifetime of Astronomy Cast we will do the show we finally know what dark energy is. After we do the show where we say we finally know what dark matter is, we will do both those shows. This is my promise to all of you.

Dr. Pamela Gay:         And this is where it’s just sort of like we can hope, and when that finally happens is that when we retire?

Fraser Cain:                 No, no.

Dr. Pamela Gay:         Okay.

Fraser Cain:                 Because there will be there will be a hundred new mysteries that are even –.

Dr. Pamela Gay:         We keep going until we die.

Fraser Cain:                 Yeah, there will be a hundred new mysteries that are even more complicated and more troubling, so, no, that’s how this whole process works. All right, Pamela, thanks a lot.

Dr. Pamela Gay:         Thank you. And thank you to all the patrons out there. I don’t actually have a thing of names, I just discovered, to pull out because it’s the very beginning of the month and the list hasn’t been generated yet but I do want to say thank you to all of you. We have been reading the names of just a subset of you on air, it’s one of the perks associated with the different levels but we love all of you, whether you’re a $1.00 a month contributor or a $100.00 a month contributor. You allow us, through our ongoing efforts, year after year to allow us to pay our humans and keep the show going, and occasionally replace cables from my camera when they die. So, thank you.

Fraser Cain:                 I will take this opportunity then to sort of mention a trend, a disturbing trend that you who are a fan of educational content should be aware of and that is artificial intelligence generated content.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 That more and more websites are moving to this model of getting ChatGPT and other artificial intelligence to generate en masse the material and this trend is going to accelerate.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 And it’s just another career that is gonna be –.

Dr. Pamela Gay:         Go away.

Fraser Cain:                 Go away, sunsetted. The career of the science communicator and that’s because it’s way cheaper to let a large language model generate explainer content. And hopefully, Pamela and I have value and place in this society as more and more of this content shifts into being generated by enormous databases. I know it sounds shocking and surprising but this is where it’s all gonna go and it’s gonna happen startlingly fast. So.

Dr. Pamela Gay:         We have had people write in and say, hey, why don’t you switch over to using ChatGPT to generate your scripts.

Fraser Cain:                 Right.

Dr. Pamela Gay:         It’s already people are suggesting it.

Fraser Cain:                 Yeah, yeah.

Dr. Pamela Gay:         And we won’t do that.

Fraser Cain:                 Yeah. I will get ChatGPT to recommend ideas but I won’t –. See, here’s the key, there are no scripts, that’s the trick.

Dr. Pamela Gay:         Right, right.

Fraser Cain:                 So, how could we have a script if there are no scripts? Smart. Anyway. So, if the work that we’re doing, like if the loss of science communicators at the mainstream media was already troubling to you, now they’re coming for all science communicators. So, if supporting the work that we do is important to you to make sure that we can keep doing the show, paying the people on the team, keeping the servers running, all of that, join our Patreon.

Dr. Pamela Gay:         Thank you.

Fraser Cain:                 Patreon.com/astronomycast. Thanks, everyone, and we’ll see you next week.

Dr. Pamela Gay:         Bye-bye.

Back to Top

Astronomers have made extremely accurate measurements of the expansion rate of the Universe and come up with different results. And the error bars for the observations don’t overlap, so there’s something strange going on. What’s the answer and how can the Crisis in Cosmology be resolved?

Show Notes | Transcript

See Comet ZTF (C/2022 E3) Dash Between Big and Little Dippers (Sky & Telescope)

Comet Hale-Bopp (NASA JPL)

Comet Hyakutake (NASA JPL)

Comet NEOWISE, the best comet of 2020 (EarthSky)

Comet McNaught over the Pacific Ocean (ESO)

Hubble Tension Headache: Clashing Measurements Make the Universe’s Expansion a Lingering Mystery (Scientific American)

Hubble telescope refines universe expansion rate mystery (Space.com)

Megaparsec (Swinburne University)

Messier 87 (NASA)

Andromeda galaxy: All you need to know (EarthSky)

Ask Ethan: Is there a better way to measure cosmic time? (BigThink)

Type Ia Supernova (Swinburne University)

How do astronomers measure the brightness of something? (Astrobites)

Luminosity (Swinburne University)

Standard Candle (Swinburne University)

What are Cepheid Variables? (Universe Today)

Gravitational Lensing (Hubblesite)

Dr. Adam Riess (Space Telescope Science Institute)

Astronomical deep-sky photometry and spectroscopy (BBC Sky at Night)

Gaia (ESA)

Baryon Acoustic Oscillations (NASA)

COBE (NASA)

Planck (ESA)

LAMBDA – ΛCDM Model of Cosmology (NASA)

Astronomers Grapple with JWST’s Discovery of Early Galaxies (Scientific American)

How Did Inflation Happen — and Why Do We Care? (Space.com)

The Big Bang (NASA)

IMPROVING MEASUREMENTS OF THE COSMIC EXPANSION WITH GRAVITATIONAL WAVES (LIGO)

Cosmic Inflation Theory Faces Challenges (Scientific American)

Sloan Digital Sky Survey

The Dark Energy Survey

JWST (NASA)

Back to Top

Transcriptions provided by GMR Transcription Services

Fraser Cain:                 AstronomyCast, Episode 668, “The Crisis in Cosmology.” Welcome to AstronomyCast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?

Dr. Pamela Gay:         I am doing well. How are you doing?

Fraser Cain:                 Doing great. Yeah, nothing to report.

Dr. Pamela Gay:         That, I think, in 2023, is really the best any of us could ever ask for.

Fraser Cain:                 Yeah, the weather is fine, the snow is gone, I’m getting out and doing a bunch of hikes and stuff in the nature, even though it’s wintertime, but still, garden’s coming along.

Dr. Pamela Gay:         Dang.

Fraser Cain:                 I saw the comet last night. It sucks, but…

Dr. Pamela Gay:         Oh well.

Fraser Cain:                 Yeah, it’s gotten quite diffuse at this point, so although it’s bigger and brighter, it’s also more of just a cloud.

Dr. Pamela Gay:         It’s spread out, so the light from any given place – its surface brightness is really low.

Fraser Cain:                 That’s right, so you really don’t get that nice, little, tight nucleus with the tail, you just get this – what looks like a little cloud in the sky. But still, it’s easy to find. It’s so easy to find because it was right beside Ursa Minor, right beside the Little Dipper, and then, it’s moving towards Cassiopeia. So, if you have never seen a comet – you can’t see it with your eyes, but you can see it in a pair of binoculars or a small telescope. It’s easy to find, and that’s nice, as opposed to one where it’s in a fairly difficult constellation to discover. But unfortunately, completely inaccessible now to the folks in the Southern Hemisphere, so this one is just for the folks in the north. So, if you haven’t already –

Dr. Pamela Gay:         Who do not have cloud like the Midwestern folks in the north.

Fraser Cain:                 Right, yeah. It’s gonna peak in just a couple of days from now, so now is your chance, and then it’s just gonna get – but it mostly sucks. I always compare comets to Hale-Bopp and Hyakutake, and people are even like, “Oh, didn’t you like Comet NEOWISE?” I’m like, no.

Dr. Pamela Gay:         No.

Fraser Cain:                 No, it sucked. I could see it with my eyes. That does not a good comet… That is necessary – sufficient but not necessary? Anyway, just barely being able to see a comet with the unaided eye does not – you do not declare victory in the comet world. No, you want the one that is gigantic –

Dr. Pamela Gay:         The tail.

Fraser Cain:                 The tail spans multiple handspans across the sky, that you can see it even in light-polluted skies. That’s a comet, and everything else the universe is sending our way right now is mediocre, and I reject them. So, no, NEOWISE sucked, McNaught sucked, this one sucks. We demand better. I will wait, but I’ve been patient for too long. Come on, comet!

Dr. Pamela Gay:         I…I can’t argue with that. All of that is true. It’s all true.

Fraser Cain:                 Yeah. For people who are like, “Oh yeah, Comet NEOWISE was fine,” no, it wasn’t! It wasn’t, and you’re settling. You deserve better. I deserve better. We deserve better comets. The universe can provide it; it’s done it in the past. It’s time to put up or shut up. All right.

Dr. Pamela Gay:         Yeah…

Fraser Cain:                 Astronomers have made extremely accurate measurements of the expansion rate of the universe and come up with different results, and the error bars of the observations don’t overlap, so there’s something strange going on. What’s the answer, and how can the crisis in cosmology be resolved? So, what is the crisis in cosmology?

Dr. Pamela Gay:         So, some people call it the Crisis, some people call it the Hubble Tension. A lot of us just put “WTF?” and call it a day. So, what’s happening is before the supernova teams did such an amazing job of measuring the present expansion rate of the universe, we were like, “Nah, the universe is expanding somewhere between 50 kilometers per second per megaparsec to 100 kilometers per second per megaparsec,” and I had so many profs that were like, “Just use 100. It makes the numbers easier.” It was pleasing.

Fraser Cain:                 Right. Just so people understand this idea, that you take a megaparsec of space, which is about 33 million lightyears of space, and when you think about that, that is the distance between us and faraway galaxies, like Andromeda’s really close. We’re talking about galaxies that are 30 million lightyears away, like M87 is kind of in that – when you think about the supernova image. Every second that goes by, those objects are now 100 kilometers farther apart, or 50 kilometers farther apart.

Dr. Pamela Gay:         And it is a function of how far something is away from you, so the further something is away, the faster it appears to be moving away from you. A lot of people use a raisin bread analogy on this because the raisins stay the same size as the bread dough expands, so two raisins that start really close together will end up a little further apart, two raisins that are really far apart initially will end up seriously far apart by the time that bread is done rising.

Fraser Cain:                 And why is knowing the expansion rate of the universe important?

Dr. Pamela Gay:         It’s one of those things that allows us to put together all the rest of our cosmological ideas of how you go from our universe being a single point to expanding out, to forming hydrogen and helium, trace amounts of lithium and beryllium, to – the whole story is tied up, and it slowed down or it sped up, and understanding what rate we’re going now, since there’s no accelerator pedal that we know about, what we see has to be defined by the physics of our universe, and we can start to define all that physics of the universe if we know this one number that refuses to be measured.

Fraser Cain:                 I apologize, I was off by a factor of 10 there, so, sorry, and you should have caught me – it’s surprising you didn’t – but a megaparsec is 3.3 million lightyears, not 33, so Andromeda, roughly, is in that ballpark range. So, apologies.

Dr. Pamela Gay:         Yes. The way I think about it is someone in Andromeda looking back at us would be seeing Neanderthals.

Fraser Cain:                 Right, but astronomers don’t think in lightyears, they think in megaparsecs, so if I get off by a factor of 10, that’s fine by you because you don’t even think about it, so apologies in –

Dr. Pamela Gay:         It’s true.

Fraser Cain:                 Yeah, the general public thinks in lightyears while astronomers only think in parsecs and megaparsecs, but yeah, so, apologize, let’s continue. So, why – you were discussing why knowing the expansion rate of the universe is important.

Dr. Pamela Gay:         It basically just gives us this reference point that we can work all the other maths back from.

Fraser Cain:                 So, how long the universe has been around for?

Dr. Pamela Gay:         How long the universe has been around for, basically –

Fraser Cain:                 What will happen in the future…?

Dr. Pamela Gay:         The one that gets me is by understanding the current expansion rate, we can actually figure how fast the universe went from being a mostly smooth distribution of gases to forming galaxies, to forming galaxy clusters. The rate at which we formed large-scale structure, at a certain level, hinges on how fast our universe is expanding. It’s everything.

Fraser Cain:                 Right. And so, in the olden days, we used to get “How old is the universe?” and people would say, “Well, it’s kind of somewhere between 10 and 20 billion years old,” and that’s that range of measurement. If you get 50 kilometers per second per megaparsec, you get one age of the universe because you just measure how long the universe is expanding, but if you get 100, you get a different one, and they are very different, and knowing that is important. So, how do astronomers measure the expansion rate of the universe at the close and at the far?

Dr. Pamela Gay:         So, there are two totally different suites of mechanisms. The “local time” way of doing it is we look for supernovae, which give off a set amount of light if they’re Type 1A supernovae – explode a white dwarf star, and you get essentially the same explosion over and over and over again, with errors that we’ve discussed in other episodes.

Measure how bright that explosion appears, measure how fast the galaxy the supernova is in is moving, and this tells you the distance using measured brightness and known luminosity, and it tells you the expansion rate by looking at the Doppler shifting. So, we’re literally measuring how much the colors of the different bands of atomic lines have been shifted by the galaxy’s motion, and that gets us a velocity.

Fraser Cain:                 Right. And so, we have all of these standard candles, from the Cepheid variables, to the supernova, to – I saw a list. There must have been 30 potential standard candles overlapping, going from – some of which are very well known, others of which are poorly known, but you go from local measurements using parallax that overlaps with Cepheid variables that overlaps with Type 1A supernova, and you just get this really beautiful, smooth measurement, and what number did we get from the local methods of measuring the expansion rate of the universe?

Dr. Pamela Gay:         So, we’re getting around 70 kilometers per second per megaparsec, and this is using not just supernovae, but as you point out, there’s a bunch of other methods. So, folks are looking at red giants, they’re looking at planetary nebulae, they are looking even at the distant gravitationally lensed galaxies that we’re able to see multiple versions of using crazy geometry when we can see the galaxies’ lenses do the same thing at different times. All these methods are giving us definitely over 70, and narrowing in on 74, so it seems pretty constant.

Fraser Cain:                 Right, and the error bars are really tightening up. The quality of the observations is exquisite. I talk to a lot of astronomers, and they talk about how good of a job they’ve done with those observations, and they just gush.

Dr. Pamela Gay:         The SHOES survey by Adam Reiss – they’re quoting an error of 1.3%, and they are basically going from the nearby Cepheids that they have taken some of the most precise photometry of that anyone has ever taken, then using Gaia parallax data, and then working all the way out. How often does anything in astronomy get done with that level of accuracy? We know this. The local value is basically 74 kilometers per second per megaparsec.

Fraser Cain:                 Right. And so, let’s go the other end of the range because there is another group of measurements that are taken not locally.

Dr. Pamela Gay:         Right, and this is where things are squirrely. In the cosmic microwave background, we see these baryonic oscillations, these soundwaves that move through the early universe, causing slight over- and underdensities, and we can map so beautifully this distribution with our theoretical models, and by combining our understanding of, okay, the universe had this much regular matter, this much dark matter, this much – putting all of these base understandings that we come at from the theory, combining our average temperature information that we got from COBE and other missions, putting it all together, it gets us in the 60s, 68, generally.

Fraser Cain:                 But the most accurate version of this was the Planck satellite from the European Space Agency.

Dr. Pamela Gay:         Right, and this is where it’s important to note the Planck data was used to get at that distribution of baryonic oscillations, and that was used in combination with a mean temperature that they were, in a lot of the papers, referring back to COBE data. So, Planck got us, very specifically, deviations about the mean, and we just fed all the data together in the context of what’s called lambda cold dark matter.

This is a theoretical framework that says that our universe is not just expanding, but it’s accelerating as it expands, that the dark matter, the stuff that we’re not really sure what it is, that may be related to neutrinos in some way – whatever it is, it wasn’t moving extremely fast early in the universe, so that’s where the “cold” part comes in. So, we have lambda, the dark energy, and cold dark matter, two things we have very poor understanding of. When you combine those with the data, it gets you, again, roughly 60 kilometers per second per megaparsec with error bars that don’t overlap.

Fraser Cain:                 Right, and this is the key. So, you look at the local neighborhood and you get a measurement that’s in the low 70s with very tight error bars, you look at the early universe, you get 68 with very tight error bars. Both are exquisite observations, both are trying to tell you the same thing, and they disagree with one another, and this, at the heart, is the crisis in cosmology.

Dr. Pamela Gay:         Correct.

Fraser Cain:                 So, this is the crisis in cosmology, so what’s the answer?

Dr. Pamela Gay:         Well, this is where I personally am a bit excited, and I don’t know how many people are with me on this one because I wasn’t at the meeting, but at the American Astronomical Society meeting, there was a lot of discussion about how JWST images of gravitationally lensed early galaxies appear to be showing from two different studies that have both made it through peer review that there were already well-formed galaxies 350 million years after the Big Bang, and that’s early.

There is other work that is being done that is still going through peer review that is showing there may have already been galaxies – massive ones – at 200 million years after the Big Bang. So, with galaxies forming this early in the history of the universe, it tells us that that model we have, lambda cold dark matter, is off somewhere because while we thought there would be a couple, a few massive galaxies early on, those baryonic oscillations didn’t lead us to believe there would be as many as we are now finding.

And so, we have to figure out a new way to get from mostly smooth universe with the cosmic microwave background to galaxies forming in bigger and probably larger numbers than we anticipated to our present structure, and folks are putting out ideas like maybe there was a bit of leftover inflation, maybe the value of dark energy hasn’t been constant, and all of these different ideas – I don’t think we can really throw anything out yet, and I am the first person to want to throw out ideas.

Fraser Cain:                 Right. So, the challenge here is that you’ve got – the most obvious possibility is that one or both measurements is incorrect –

Dr. Pamela Gay:         Yes.

Fraser Cain:                 – which is what would be everybody’s first instinct, that someone’s wrong, that one of these measurements is incorrect. But, because of this dichotomy, both measurements have been scrutinized and scrutinized, and teams have gone back, and all they’re doing is narrowing the error bars. They’re not finding a large discrepancy. So, that’s the one that is most likely, and yet, that seems to be less and less of the case, and so, you’re left with the universe –

Dr. Pamela Gay:         New physics.

Fraser Cain:                 New physics, right, that our understanding of Einstein, our understanding of what those acoustic oscillations should be in the cosmic microwave background, is wrong.

Dr. Pamela Gay:         And this is where I’m not gonna lay blame on anybody. Relativity seems to work so far, it doesn’t seem to be the problem, but our understanding of the distribution of kinds of matter, the way different forces interplayed, whatever the heck inflation might be – we have no idea what inflation might be – it is somewhere in this physics of how we get from the Big Bang to now that we are missing something, and it’s kind of awesome.

We don’t get a whole lot of surprises anymore, it feels like, some days. We’ve found all the particles in a standard model. We didn’t find any of the particles from supersymmetry. This gives us something new to chase, and the fact that even the folks using gravitational waves to measure distances – they’re still getting the same local universe numbers.

Fraser Cain:                 And that’s harder to get wrong.

Dr. Pamela Gay:         Yeah!

Fraser Cain:                 I know I’ve talked to some people working in gravitational wave observatories, and I’ve had this conversation, and effectively, the more precise, the more powerful these gravitational wave observatories get, the farther they’re able to see out into the universe. You can rely on their measurements, so it’s another layer of observation, but one that’s very trustworthy, and it only goes so far. It doesn’t take you all the way up to the end of the universe, but maybe some future observation will.

So then, new physics – so, maybe we don’t understand how the early cosmic microwave background worked, maybe we don’t understand how Cepheid variables work, maybe we don’t understand all these different pieces, but there have been a few hints. Maybe Type 1A supernovae aren’t the standard candles that we thought they were.

Dr. Pamela Gay:         And this is where there are so many different things that are getting us that local 73-ish that, yeah, I’m happy saying there are discrepancies from one Type 1A supernova to another in weirdo special cases. We’ve got to talk about some of those. If the white dwarf ends up inside of another star, that explosion’s gonna be a bit different, and that happens, but it really seems like there is something about how you get from there – cosmic microwave background – to here – gravitational waves, Cepheids, planetary nebulae, supernovae, all these other mechanisms. There’s something in the science that we have yet to uncover.

Fraser Cain:                 And then, another possibility is if the rate of expansion of the universe changed. So, perhaps there was a – the model that I’ve heard is this idea of late inflation.

Dr. Pamela Gay:         Yeah, that’s the one I was looking at as well, where whatever it was that caused us to initially blow up, there’s a little bit of that left over that caused another kick, but we don’t understand what’s going on there.

Fraser Cain:                 Right, right. And so, if you had an expansion rate of 74 early on – or, sorry, 68 early on, and then it slowed down, you could get the one that’s today, and that’s even taking into account dark energy. I’m sure people are like, “What about dark energy?” That’s layered on top of this. That’s accounted for. And so, you would have this almost – instead of the universe smoothly applying the accelerator on the gas, it was like putting the accelerator a little harder, and then pulling the foot off the pedal a little bit, and then putting it on harder again, and who knows what kind of shenanigans it got up to in the intervening period? So, what is the way forward at this point? What is the way out of the crisis in cosmology?

Dr. Pamela Gay:         We need to basically do a survey of just what was the distribution of galaxies and galaxy clusters in the early universe. We have done a beautiful job, first with the Sloan Digital Sky Survey, doing a volume around our galaxy. Then, with the Dark Energy Survey, we have pushed out even farther in some areas of the sky. With JWST, we’re going to be able to continue pushing the survey of structure size further and further out, watching how the universe goes from being Swiss cheese with giant holes in it to being Swiss cheese with smaller and smaller holes in it –

Fraser Cain:                 Right.

Dr. Pamela Gay:         – and by measuring how that large-scale structure changes over time, that will start to put a different form of constraint on our models. We need to be out there, counting early galaxies.

Fraser Cain:                 Right, and so, you’ve got this structure of the cosmic microwave background radiation, and the hot spots and cold spots should map to equivalent clusters and distributions of galaxies, and so, you’ll know that this transition from the farthest that you can see to more recent is smooth –

Dr. Pamela Gay:         Yes.

Fraser Cain:                 – and then, that will tell you, and you can keep moving forward at that point, but that’s a much harder observation. Weird as it sounds, the galaxies are much dimmer and harder to spot and map out than the cosmic microwave background radiation, which is everywhere in all directions.

Dr. Pamela Gay:         Yeah. More telescopes.

Fraser Cain:                 Yeah. And then, the other side of that is going farther with gravitational waves, and hopefully, you’ll get to this point where the two overlap, where the gravitational waves reach the cosmic microwave background, or shortly after.

Dr. Pamela Gay:         That is technology that someone maybe someday will fund, and we’re at that frustrating point where the next big discovery beyond what we can do with the new, massive radio telescopes that have started to catch star formation at earlier periods, and what we can do with JWST – it’s gonna take multiple nations getting together to build these 30-, 80-, however-many-meter telescopes that are being discussed to be able to look back.

Fraser Cain:                 All right, place your bets. It’s the close observations are wrong, the CMB observations are wrong, or there’s new physics.

Dr. Pamela Gay:         New physics.

Fraser Cain:                 Really? That’s the most exciting outcome possibility, is new physics, so if that’s true, that would be wonderful.

Dr. Pamela Gay:         Or at least a new understanding of that cold dark matter temperature.

Fraser Cain:                 It would be huge thing, like there was a revision to relativity that nobody saw coming.

Dr. Pamela Gay:         So, again, I’m not sure saying a revision to relativity is the right way to say it because I think that what we’re looking at is something coming out of the realm of particle physics, and particle physics and relatively do not talk to one another, and I really think it’s going to be something about how particles interact in different regimes, and whatever the heck this dark energy is that’s gonna be what gets us to the solution to this discrepancy.

Fraser Cain:                 I think this “crisis” makes it sound like a bad thing, but you talk to astronomers, and they couldn’t be more excited. They’re so happy to not understand something, what was considered to be this bedrock idea, because the problem is bedrock is you get this ossification. Suddenly, you have this space that has opened up, where the solution is in there somewhere, and a lot of interesting ideas and theories, and a lot of brainstorming, and a lot of intellectual power gets to be put onto this problem, and they love it. They love it. So, I feel said that the term “crisis” – because you get a lot of pseudoscientists sort of rolling their eyes at scientists at this thing.

Dr. Pamela Gay:         I like “the Hubble Tension.”

Fraser Cain:                 “Hubble Tension” – yeah, but “Crisis in Cosmology” is a better name, so I’d rather reel them in with “the Crisis in Cosmology,” and then help people understand that, in fact, astronomers couldn’t be more excited and happy to have this opportunity. All right, Pamela, thank you so much.

Dr. Pamela Gay:         Thank you, Fraser, and thank you to everyone out there who makes this show possible through your patronage at Patreon.com/AstronomyCast. This week, I would like to thank Camy Raissian, Gabriel Gauffin, Benjamin Davies, Steven Coffey, john öiseth, Arcticfox, Dean, Corinne Dmitruk, Bart Flaherty, The Lonely Sand Person, John Drake, Nate Detwiler, Lew Zealand, Brian Kilby, Naila, The Air Major, Ron Thorrsen, Arthur Latz-Hall, Leigh Harborne, Jason Kardokus, Robert Hundl, Kim Barron, Paul Esposito, Ruben McCarthy, Bob Zatzke, Jordan Turner, Timelord Iroh, Daniel Donaldson, Frank Stuart, Ian Abdilla, and Geoff MacDonald. Thank you all so much for making everything we do possible.

Fraser Cain:                 Thanks, everyone, we’ll see you next week.

Dr. Pamela Gay:         Bye-bye.

Voiceover:                   AstronomyCast is a joint product of Universe Today and the Planetary Science Institute. AstronomyCast is released under a Creative Commons attribution license, so love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, AstronomyCast.com.

This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at Patreon.com/AstronomyCast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been AstronomyCast.

Back to Top

As astronomers look out across the Universe, they see various objects spewing jets of material light years into space. What causes these jets, and what impact do they have on the Universe.

Download MP3 | Show Notes | Transcript

PDF: The Role of Magnetic Fields on Astrophysical Jets (arxiv)

What is the Interstellar Medium? (University of New Hampshire)

Angular Momentum (Swinburne University)

Ideal Gas Law (Hyperphysics)

How to Make an Engine from a Battery, Wire and a Magnet (WikiHow)

How Rail Guns Work (How Stuff Works)

Binary Star (Swinburne University)

Einstein’s theory of general relativity (Space.com)

Frame-dragging (Einstein Online)

T Tauri Stars (Swinburne University)

Herbig-Haro Object (Swinburne University)

What is a neutron star? (EarthSky)

What Is a Black Hole? (NASA)

IMAGE: A cosmic searchlight (ESA)

Stanford astrophysicists report first detection of light from behind a black hole (Stanford University)

Gamma Ray Burst (Swinburne University)

Quasar (Swinburne University)

A stellar vampire mimics a black hole (Physics Today)

Back to Top

Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast, episode 635: Astronomical Jets. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela. How you doing?

Dr. Gay:                      I am doing well. How are you doing?

Fraser:                         Also well. Sort of dealing with the trials and tribulations of getting our house completed. We’re in the final stretch now and it’s all the little details that need to be done perfectly and each one can hold up the thing. But we’re getting there. We’re getting there. As astronomers look out across the universe, they see various objects spewing jets of material light years into space. What causes these jets and what impact do they have on the universe? All right, jets. Now, we’re not talking about aircraft jets. We’re talking about space jets. But they’re not aircraft jets in space. What is a jet?

Dr. Gay:                      So, at the most simplistic level, a jet is anytime you have something that sends out materials at high velocities. So, when we call an airplane a jet, what we’re actually referring to is its engines that are spewing material out at high velocities instead of just having a propeller at the front.

Fraser:                         And throwing an airplane in the opposite direction.

Dr. Gay:                      Exactly. Exactly.

Fraser:                         Right.  

Dr. Gay:                      Now, in astrophysical situations, we are talking about situations where you have some sort of an object that has a entire environment around it that is leading up to it sitting at the center of normally bipolar, going-out-in-two-different-direction jets that have been built up most typically by a magnetic field.

Fraser:                         So, I guess, think of a fountain throwing water high up in the air. The distance that the fountain goes is limited by the force of gravity, so it reaches sort of a maximum height. It’s running into the air, and so you’re getting both the jet getting a little bit slowed down but also sort of broken apart a little bit as well as other spray and material going off in all directions; except with the astronomical ones, they go in two directions, so you’ll get jets, as you say, in polar directions.

Dr. Gay:                      And the gravity of the object can, if it doesn’t make it very far away, cause the material to flow back at you. But most of the time, as the material’s getting kicked out at such high velocities, you don’t really see this – we refer to it as collimated – getting focused into a tight beam. We don’t see that focused beam start to diffuse out into a cloud of material like at the top of a fountain until it hits that interstellar media, until it hits all the stuff that is just filling space between galaxies or between stars.

Fraser:                         Right, right. I guess there’s not that much to run into.

Dr. Gay:                      Depends on the system.

Fraser:                         So, what can generate these jets? What is their cause?

Dr. Gay:                      The bulk of the time it is extremely complex physics where the correct is, we don’t entirely know.

Fraser:                         You can’t just say “extremely complex”. “The answer’s “extremely complex physics”.” That is unsatisfying to me.

Dr. Gay:                      I know. I know, and this is why in introductory textbooks, magazine articles, all that complicated physics gets hidden behind the phrase magnetic fields.

Fraser:                         Perfect. Now, we’re talking. It’s magnets.

Dr. Gay:                      And the truth is there are magnetic fields that are involved, where you have this compact object that has materials spiraling around it and it’s often getting either stolen off of another object or it’s flowing in the center of a galaxy. And as it comes in, it is getting denser and denser and denser because the material has to shed angular momentum in order to get in towards the center. So, it backs up while it’s going through this process of shedding angular momentum, and this built-up material gets denser and it gets hotter due to that PV nRT equation that we learned in high school. Chemistry, pressure, density, temperature, all related things.

                                    And if it gets hot enough, it can even start having nuclear reactions. So, hot gas, it’s gonna eventually become, hot ionized gas. And hot, ionized gas means that you have atoms that have shed electrons away and these are now charged objects. Charged objects orbiting are charged objects going in a circle. Moving charged objects create magnetic fields. Moving charged objects going in a circle create basically electromagnetic fields like a battery and some wire can do, and you’ve now built a very small railgun that can fling things out of the magnetic field along these polar axes.

Fraser:                         All right, so you’ve got matter moving at high speed crushed together, heated up to enormous temperatures, starting to undergo more exotic processes like fusion. But ionization of these particles, they’re moving in circles around whatever object they’re orbiting. This is generating electricity, magnetic fields, and complex physics, that soup of madness, is now creating this, as you call it, a Gauss gun, a railgun, a magnetic accelerator that has been taking this raw material and hurling it away from the accretion disk.  Right.

Dr. Gay:                      And what I love is, at the most simplistic level, this is something you could do with a sixth grader: wire batteries and a tiny magnet. So, go figure this out for yourselves, people.

Fraser:                         And feeding material from a binary companion star or generating nuclear fusion. Any sixth grader can do this. All right, so we got a sense of what the underlying complex physics, or at least the ingredients of the mess, that is happening. And I think you said it perfectly. Astronomers still don’t know. Some of the finest minds in nuclear physics, in particle physics, in magnetic field, in fluid dynamics, in all of these fields working together are still arguing and discussing.

Dr. Gay:                      Lemme give you one example.

Fraser:                         Also, relativity has effect as well.

Dr. Gay:                      Frame-dragging.

Fraser:                         Frame-dragging.

Dr. Gay:                      Frame-dragging is a thing. And to give you one example of why this is confusing. If you go back to your sixth-grader model. Literally you can do this. Go grab some wire that isn’t insulated the way this is, wrap it in a circle, attach both ends of the wire to a battery and now you have charge flowing and you can use this to fling small objects. It’s fun. If you get big and fancy, car battery, PVC wrapped in wire. Now, you have a small railgun. Now, when you build your small railgun, it is always going to fling magnets in the same orientation. With galaxies, you have electrons being thrown both directions out of this, and so you have to build up a system that allows symmetrical flinging of materials in both ways.

                                    Now, electrons have both north and south magnetic orientations. There’s ways to get there, but just understanding it is flinging things in a symmetric manner. It’s kind of –

Fraser:                         Right.  

Dr. Gay:                      – where you get at the “This is hard”.

Fraser:                         But it’s perpendicular to the axis of –

Dr. Gay:                      Right.

Fraser:                         – rotation of the object. So, if the galaxy is –

Dr. Gay:                      Right-hand rule.

Fraser:                         – rotating, right-hand rule. You’re gonna see material blasting up out of the center of the galaxy and also down out of the center of the galaxy in completely opposite directions of the galaxy. All right. Again, I guess I say, “We know why this happening.” We don’t know why this is happening. All we know is that, in that mess of complicated physics this is happening. What kinds of objects are capable of generating these jets?

Dr. Gay:                      Okay, at the most pathetic level, we have very young stars called T Tauri stars. The bulk of a T Tauri star’s jets are due to outflows of just it’s not eating the material fast enough as it flows down onto the star and things escape. But, also, its magnetic fields will bloop out material in pockets now and then, so you have ineffective bloopy jets coming from T Tauri stars. Then, skip through most of the stars in between that are happily doing their main sequence and beyond life of nuclear fusion and their core, and then we get to the neutron stars.

                                    So, as soon as you get to something as dense as a neutron star, these objects become capable of gravitationally pulling stuff off a companion and getting it going fast enough around the neutron star because it has enough gravity and it’s tiny enough and you need both, that you can start getting that jet that has the magnetic field again. So, for individual objects that have long-term lasting jets, you have T Tauri stars, Herbig-Haro objects at the very beginning; things forming stars. Stars are happy, stars are happy, stars are happy, stars die. And for dead stars, you have neutron stars and bigger. And when I say “and bigger” I mean, all black holes all the way up to super black holes are capable of having jets. So, you can have a full fledge galaxy that has the exact same, not-entirely-well-understood physics as the neutron star.

Fraser:                         It’s just a matter of scale?

Dr. Gay:                      Yes.

Fraser:                         Right. All right, so let’s talk about scale then. We talked about how a neutron star will generate some level of jets, and super massive black holes, the most massive objects in the universe, will generate these jets. What is the scale? How far out can these jets go from their source?

Dr. Gay:                      Light years and light years and light years and light years, by which we’re talking thousands and thousands and thousands of light years from the center of a galaxy. And the image of those of you who happen to be watching on YouTube or live while we’re recording on Twitch, there is a tiny speck that, on my particular monitor is the size of my pinky fingernail, that represents where the galaxy is. And about 6 inches away in this image is where the jet ends, and the jet is actually pointed a bit at us, so that’s hiding some of the full length of this jet. In the radio sky, galaxies are a very different size than they are in the optical sky because of how big these jets are.

Fraser:                         So, for a neutron star, we’re talking like dozens of light years?

Dr. Gay:                      It can be. Now, the neat thing about neutron stars and stuff is they exist in much more complicated parts of our galaxy, so their size is going to be beautifully dependent on how much stuff is around them. And so, we can end up with, they go out and now they’re pushing their way out, blowing a bubble around them. And it’s this blowing a bubble around them that, at a certain degree, allows us to figure out how long they’ve been doing things in some cases.

Fraser:                         Because you know how fast the material’s moving and then that lets you figure out when it started this process? Okay.

Dr. Gay:                      Yeah. And so, you’re looking at different kinds of environments, but what is particularly fascinating is when we look back at the center of our galaxy, even from what we are, in the correct wavelengths of light we see all these bubbles all over the place. Some of them are spherical bubbles that are created by supernova explosions. But in other cases, what we’re seeing is the material pushed out by jets.

Fraser:                         That’s really fascinating. That you look at the universe in these different wavelengths, and now you see this historical record of the events. You see bubbles blown out from ancient supernovae. You see the wakes of jets released by neutron stars while they were actively feeding on some companion star or black holes while they were feeding on some companion star. And I’m guessing we see something similar for galaxies with active nuclei that we can see how things have changed over time with them.

Dr. Gay:                      I’m not sure we’ve actually seen something like that, but it could be I’ve missed it in the literature.

Fraser:                         There was a paper that I recall where they were seeing the material falling back in or they were seeing light echoes from the jet.

Dr. Gay:                      So, light echoes we see.

Fraser:                         They were seeing light echoes from the jet that was allowed them to figure out when it was an active galaxy. And it’s not an active galaxy right now.

Dr. Gay:                      Light echoes are fairly common-ish in the grand scheme of, we’ve seen more than three now. I’ve been in astronomy long enough that, anytime you see more than three, that’s awesome; but in terms of just seeing a galaxy clear out the world around it and no longer be doing that, that’s what I’m not sure we’ve seen. So –

Fraser:                         Right, right.

Dr. Gay:                      – we’ve seen a light echoing, but what’s awesome to me, and what I can’t wait for us to see the relics of is supernova explosions in just the right format, specifically gamma ray bursts. They have the shockwave going out in a sphere that may be interrupted by planetary disks and things, but generally going on in a sphere or bipolar outflows that is caused by the star itself exploding. But what we’re now starting to think is, in some cases where you have a nearby companion, the material that’s getting shot off can quickly spin up in a disk as it gets the companion creating this gamma ray burst. That’s only one of several explanations of a gamma ray burst. It’s the one I like the best.

Fraser:                         Right.

Dr. Gay:                      Whatever the source of these gamma ray bursts is, you end up with tremendous high-energy jets that last very briefly and are capable, we think, of destroying planets several hundred light years away.

Fraser:                         Several tens of thousands. It will cause damage.

Dr. Gay:                      Is it 7,000 or 700? It will cause damage.

Fraser:                         It will cause damage. If it’s a few hundred light years away, it will destroy planets –

Dr. Gay:                      You’ll have roasted rock left behind.

Fraser:                         – right. But even if you’re halfway across the galaxy –

Dr. Gay:                      Ionizing radiation.

Fraser:                         – the ionizing radiation will blast away your ozone layer and everybody will get cancer and die.

Dr. Gay:                      But the planet will recover. We believe we have experienced –

Fraser:                         Right.

Dr. Gay:                      – that in our past, the world is still here. Within a few hundred, you basically have Mercury left behind.

Fraser:                         And good news, there are no stars capable of going gamma ray burst in our vicinity that we know of. All right, so you talk about like one impact of a gamma ray burst with jets, but what influence, what effect do these jets have on their galaxies and the areas surrounding them.

Dr. Gay:                      You clearly don’t wanna get into one of them because they’re a source of ionizing radiation. They are giving off loud radio signals. So, communications near them is certainly going to be difficult, but in general it’s that disk that is generating them that I’d be afraid of because that is giving off a truly amazing amount of light in the center of a galaxy. The jet is going out of the galaxy, so you can sit there and go, “Oh, beautiful”. But that accretion disk in the galaxy you’re living in that is generating this disk, for super massive black hole ones, there’s another word for that disk. That’s a quasi-stellar object.

Fraser:                         Quasar.

Dr. Gay:                      And so, the light from that has the potential to be dangerous to fairly large distances within the galaxy it’s in.

Fraser:                         So, I did research into this. If the super massive black hole at the middle of the Milky Way turned into a quasar, you wouldn’t see it with the unaided eye. You would need a very powerful telescope to even detect it. Because you wouldn’t staring down the throat of it the way that we were with –

Dr. Gay:                      Right.

Fraser:                         – a lot of other ones, right? To see it from the side, it actually wouldn’t be significantly brighter. But I guess what I’m getting at is you’ve got this jet of material that’s flying out kind of like a fountain, like that original analogy, and then this material is falling back down into the galaxy in some cases. What influence does that have on the galaxy?

Dr. Gay:                      So, the material coming back, just like anytime you get a shockwave, it can trigger nice, happy, sitting around molecular clouds to collapse down and possibly form stars. And I just wanna go back to what you said. With your eye, all the dust in our Milky Way’s gonna hide that accretion disk from us. The trickstery bit gets to be, there are other wavelengths of light that you’re gonna have blinding light for other instruments coming out and –

Fraser:                         Right.  

Dr. Gay:                      – this is where the sky again is so different radio versus optical.

Fraser:                         And there was another piece of research that I saw, and I don’t know if you had seen this one, that a galaxy had gotten hit with the jet of another nearby galaxy?

Dr. Gay:                      No.

Fraser:                         And they think that it might in some cases maybe cause an increase in star formation, but maybe even quenching star formation, which was quite fascinating.

Dr. Gay:                      If you blast apart areas that are forming dust, then you’ve added enough energy in that, instead of the material collapsing, the material’s gonna dissipate in the face of this wind.

Fraser:                         Oh.

Dr. Gay:                      You shouldn’t smoke, people. You should not smoke.

Fraser:                         Right.  

Dr. Gay:                      But if you imagine exhaling smoke, you have a nice little cloud here, but on a windy day, you never get the cloud of smoke.

Fraser:                         Right.

Dr. Gay:                      Let’s go with a cold day. You exhale your breath. If there’s no wind you can see your breath, if there’s a lot of wind you have no chance to see your breath.

Fraser:                         And you need a nice, cold cloud of gas to form a star.         

Dr. Gay:                      Exactly.

Fraser:                         If energy is getting pumped into it and it’s heating up –

Dr. Gay:                      It can’t collapse.

Fraser:                         – then it can’t collapse. You may have the otherproblem. But the other thing that’s interesting as well is that because you’ve got fusion going on in some of the cases of these, you’ve got heavier elements that are actually being generated and thrown out into space. And so, it might actually be another source for heavier –

Dr. Gay:                      Hemorrhage.

Fraser:                         – elements that could contribute and enrich to some of these solar nebulae. So, it’s a field that is really wide open for discovery, both their underlying cause as well as their influence and their effect. It could be everywhere from no effect to life might not exist without these jets. So, more research is needed.

Dr. Gay:                      And just you can track the history of stellar vampirism. So, while we may not have vampires on our planet, there are vampires among the stars. And if they aren’t continually sucking at their neighbors, they will have puffy jets. So, I’m just gonna leave you with that thought, that there are puffy jets of non-continuous feeders out there.

Fraser:                         Very cool. All right. Thanks, Pamela.

Dr. Gay:                      Okay, thank you, Fraser. And it’s time for me to do that thing where we thank all the amazing humans out there that make this possible. Every time I say, “I’m sorry, Rich. You’re gonna have to edit,” well, it’s because of these people that we can pay Rich and Ally and Beth and the whole team of people. Oh my goodness, Nancy, thank you for keeping us lined up.

                                    This week, I wanna thank Jeremy Kerwin, Rob Cuffe, Harald Bardenhagen, Alex Cohen, Rando, David Gates, marco iarossi, Nicky Lynch, Daniel Loosli, Phillip Walker, Scott Bieber, Brian P. Cox, David, Matthew Horstman, Matthias Heyden, Justin Proctor, Disasterina, Gregory Singleton, Nial Bruce, The Lonely Sand Person, Jim Schooler, Jeff Willson, Tim McMackin, Paul Hayden, Cooper, Nate Detwiler, Eran Segev, Allan Mohn, Benjamin Müller, Steven Shewalter, Omar Del Rivero, Kenneth Ryan, Karthik Venkatraman, Alex Raine, Paul D. Disney, Micheal Regan, Don Mundis and Dean McDaniel.

                                    And Rob Cuffe, thank you for giving me a pronunciation guide for your name. And thank you so much to all of you. If you too wish to have me vaguely pronounce your name correctly in one of our episodes – I’m so sorry – please join us on Patreon. If you would like your name pronounced correctly, add a pronunciation guide.

Fraser:                         Wonderful.

Dr. Gay:                      Thank you.

Fraser:                         All right. Thanks, Pamela. We’ll see you next week.

Dr. Gay:                      Buh-bye. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons Attribution’s License. So, love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We’re so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

Back to Top

Have you ever wanted to be a time traveler? Good news! You’re time traveling right now. Into the future at one second per second. Too long? Don’t want to wait? Good news, Einstein’s got you covered. Today, let’s talk about the weird world of time dilation.

Show Notes | Transcript

What’s Up: Mercury at Sunset and Nova in Cassiopeia (CosmoQuest)

Harvard Science Center (Harvard)

What is relativity? Einstein’s mind-bending theory explained (NBC Mach)

How “Fast” is the Speed of Light? (NASA)

The Theory Behind the Equation (PBS)

Buck Rogers in the 25th Century (IMDb)

How does relativity theory resolve the Twin Paradox? (Scientific American)

Landmark NASA Twins Study Reveals Space Travel’s Effects on the Human Body (Space.com)

International Space Station (NASA)

Speed and Velocity (Math is Fun)

COMIC: Gravity Wells (xkcd)

How to Make Your Own Gravity Well (Saint Mary’s University)

Interstellar (IMDb)

The Expanse (IMDb)

How Fast Do Spacecraft Travel in The Expanse? (Wired)

Momentum (The Physics Classroom)

Transcriptions provided by GMR Transcription Services

Fraser Cain:                Astronomy Cast Episode 606: Time Dilation. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.

I’m Fraser Cain, publisher of Universe Today. And with me as always is Dr. Pamela Gay. A senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?

Dr. Pamela Gay:         I’m doing well. It is a glorious spring day. And while the stars don’t shine as many hours each night, it is great to have Mercery over on the horizon. Have you gotten out to go look at it yet?

Fraser Cain:                I thought we went through this. I can’t see Mercury. I have no view to the East and I have no view to the West. Mercury is – I’m just gonna have to take it on faith that Mercery even exists.

Dr. Pamela Gay:         Okay. I understand. I am going to have to go to a field somewhere.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         Because I, too, have no horizon. But I have access to cornfields that don’t yet have much corn in them.

Fraser Cain:                The only time I’ve ever seen Mercery I was in Australia. That’s it. And you have the benefit that the ecliptic sort of rise is straight overhead in Australia. So, you know, as opposed to things here being very low down to the horizon.

Dr. Pamela Gay:         Right.

Fraser Cain:                But yeah. And so, someone was like, “Oh, yeah. And there’s Mercery.” And I was just like, “This is the first time I’ve ever seen Mercery.” Too great.

Dr. Pamela Gay:         I think I have seen it from the roof of a building at Harvard. The Science Center in Harvard Yard – or just outside Harvard Yard – has a small telescope on its roof that I used to work with. And light pollution always makes it questionable if you know what you’re actually looking at. Because there just aren’t enough stars. But I think I’ve seen it, but now that I live someplace darker, I’m gonna try again.

Fraser Cain:                All right. So, if people wanna see Mercery and they do have, oh, I dunno, a horizon …where and when should they look?

Dr. Pamela Gay:         So, if you go out right now it is located between the very, very bright Venus and the super-thin crescent moon. The moon’s getting higher and higher, and thicker and thicker each day. But it remains above Venus in the West/Northwest. So, go out –

Fraser Cain:                Just after sunset.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                Okay.

Dr. Pamela Gay:         Venus will pop out brightest and then look up.

Fraser Cain:                Have you ever wanted to be a time traveler? Well, good news. You’re time traveling right now into the future at one second per second. Taking too long? Don’t wanna wait? Good news. Einstein’s got you covered. Today, let’s talk about the weird world of time dilation. All right, Pamela. Time dilation. What?

Dr. Pamela Gay:         So, one of my favorite things that was like this breakthrough understanding for me with relativity. Was the understanding that no matter who you are and what you’re doing the speed of light will appear exactly the same. And in order for that to happen, how you perceive time has to change.

So, the way to think about this is what we’re used to in day-to-day life is …if I’m standing on side of the road in front of my house. And a car zips by, it appears to zip by at 30 miles per hour if they’re following the law. Now, if I’m going down the road at 30 miles per hour, the car in front of me – in theory, if they’re following the law – should appear to be moving zero miles per hour relative to me.

Fraser Cain:                Right.

Dr. Pamela Gay:         And so, we’re used to seeing everything with relative speeds. The faster I’m going, I’ll see people on the side of the road appearing to go in reverse. People around me, I see their motions relative to my own. So, it seems like using that human experience that the faster I go, I should eventually be able to catch up to those photons and perceive them as moving side by side with me.

But the reality is that while some outside observer might somehow perceive me and those light particles going at almost the same speed. I will never go as fast as the light. I will never see that. I will always see light. At the exact same speed relative to me.

Fraser Cain:                And that is such – I mean, when you think about Einstein’s ability to perceive the world in a fascinating way. To have this thought experiment that you’re traveling almost at the speed of light. And then you shine a flashlight, and you watch the flashlight. And in your mind, you be like, “Well, do I see the photons speeding away –

Dr. Pamela Gay:         Right.

Fraser Cain:                – just a little faster than me or do I see the photons speeding away at the speed of light?” And the only way – if you see them at the speed of light – is if time itself is changing.

Dr. Pamela Gay:         And so, this brings up that bizarre reality that Buck Rogers in the 21st century is actually a possible outcome of someone orbiting at a high enough velocity. Now, the fact that orbital mechanics doesn’t allow you to zip around the planet that fast. Let’s say instead they put themselves in this massive orbit at super high speeds.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         That’s more realistic. Orbit around the sun instead. But …well, good ole Buck Rogers perception of time will slow.

Fraser Cain:                Okay. So, then you talk about this idea of speed. So, let’s break down time dilation. And I mean, I wanna ask why is time dilation? But I know the answer. And the answer is because. Right? Relativity. Because that’s how the universe works. So, let’s proceed right past ‘why’ and go straight to ‘how.’ How time dilation? And there’s sort of two factors. Two ways that you can get time dilation. And the one is the speed.

                                    So, let’s break this down in some examples. And now you’re providing this example. The twin paradox is the classic one, right?

Dr. Pamela Gay:         Yes.

Fraser Cain:                We’ve got two people. One here on earth. One gets in the spacecraft. What happens next?

Dr. Pamela Gay:         Well, so we actually got to see this with the Kelly twins. And the reality is that the astronauts on the International Space Station are experiencing time ever so much slower. And the way you figure out who experiences the change in time is you look to see who experienced the force. And who experienced that acceleration that got them to that faster velocity.

                                    So, in this case, you accelerate yourself up to the International Space Station and to a velocity that keeps you circling the planet instead of falling back. And time slows.

Fraser Cain:                Right. And in that sort of very slightly –

Dr. Pamela Gay:         Yes.

Fraser Cain:                And it’s more complicated because of course the International Space Station and the twin who’s on the ground are in a gravity well. But let’s say you have the one who accelerates up to close to the speed of light. Flies for 10 years, and then returns. And then the twins meet up. So, what you’re saying is that it’s not the speed.

Dr. Pamela Gay:         Yes.

Fraser Cain:                It’s the acceleration that you experience to get yourself up to that speed.

Dr. Pamela Gay:         That determines who is the one who is experiencing the time change.

Fraser Cain:                Got it.

Dr. Pamela Gay:         It’s the velocity that you accelerate to that determines how much time slows down.

Fraser Cain:                Right. And so, twin No. 1 is sitting on earth. Twin No. 2 gets in a spacecraft. They accelerate – and that’s the key – to close to the speed of light. Compared to the twin who’s just sitting on the planet.

Dr. Pamela Gay:         Yes.

Fraser Cain:                They then return – it’d take them 10 years. Or I guess the person traveling experiences 10 years and returns home to earth to see that the twin who was on earth has experienced –

Dr. Pamela Gay:         Death

Fraser Cain:                – vastly more time.

Dr. Pamela Gay:         Death.

Fraser Cain:                Right. Right.

Dr. Pamela Gay:         Humans only live so long. The human on earth –

Fraser Cain:                Sure. Right.

Dr. Pamela Gay:         – experienced death.

Fraser Cain:                Right. And so, the twin  – so, I just want to be sure I got this clear. So, the twin who flies on the spacecraft experiences 10 years. The twin who stayed on earth experiences hundreds, maybe thousands, maybe millions of years.

Dr. Pamela Gay:         Essentially, the closer you get to the speed of light. The closer you get to stopping time for yourself while time passes for those on earth.

Fraser Cain:                Right. Because you’re experiencing the acceleration.

Dr. Pamela Gay:         Well, and so the key is who is the one whose time stops for?

Fraser Cain:                Right.

Dr. Pamela Gay:         We always see things in our frame of reference. And this is where that car idea is important to think about. So, relative to me standing on the sidewalk and the Uber driver zipping down the street. The Uber driver, if they perceive themselves as not moving. Will see me moving at 30 –

Fraser Cain:                Right.

Dr. Pamela Gay:         – miles per hour. So, if you have two spaceships in space it’s harder to sort out who’s the one moving and not than it is on earth.

Fraser Cain:                Right.

Dr. Pamela Gay:         And clearly, compared to the trees, the ground, and everything else, I’m not moving. But in the vastness of space, you stick two spacecrafts down and throw the rockets on one and don’t tell the people on board who is having the rockets thrown. You might feel it. But you can also say, “Hey, we just spun your spacecraft so you felt gravity.” So, the two could experience the same thing.

Fraser Cain:                All right. So, we talked about speed/velocity as one. And I gotta be careful, right? Because I’m using speed/velocity interchangeably. And that is bad physics, Fraser. Bad. So, velocity. Right? Velocity is speed and direction.

Dr. Pamela Gay:         So, in the equations to figure it out, they use the scalar velocity. Which is the speed.

Fraser Cain:                Okay.

Dr. Pamela Gay:         And so, for figuring out how much time has changed you can just say speed.

Fraser Cain:                Okay. Okay. All right. So, we talked about speed.

Dr. Pamela Gay:         Yes.

Fraser Cain:                And the other way is to be in the presence of a gravity well.

Dr. Pamela Gay:         It’s true. It’s true.

Fraser Cain:                And I think we’re all really fortunate because Interstellar came out a couple of years ago. And they had this happen. And so, we got to see what it did. So, what’s going on with that.

Dr. Pamela Gay:         So, the closer you get to a massive object. The way to think about it here is in a normal situation down on the planet earth, if I throw a ball slightly, I see it moving at one speed. If I throw it really hard I see it moving at another speed. And then, if I go to Jupiter and I use the exact same amount of force to throw the exact same amount of balls. They’re gonna move much slower. Because more –

Fraser Cain:                Right.

Dr. Pamela Gay:         – gravity. Now, for a poor innocent little light particle trying to escape from the super high-mass object, that light particle is experiencing all that gravity. And in order for that light particle to continue always moving at the same speed of light, time is gonna have to change as it escapes from different gravity wells.

Fraser Cain:                Right. Okay. And like we saw – you know I was talking about this idea of watching the movie Interstellar. And we saw how in Interstellar he goes down to the surface of this planet that’s orbiting around this supermassive black hole. He’s there for a day. Comes back out and the rest of the universe – the rest of his family – has experienced 80 years. Or some ridiculous amount of time.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                And so, it was not because of the speed they were doing to go through the wormhole and blah blah blah. It was because they spent this time close to the black hole in the gravity well. And so, I think, going back to that conversation that we had about the acceleration is the key.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                When you’re in a gravity well, you’re experiencing acceleration.

Dr. Pamela Gay:         Yes. It’s the – what is doing the fundamental altering of your movement through space and time. And that gravity well is doing its darndest to keep you attached to it.

Fraser Cain:                Right.

Dr. Pamela Gay:         And to keep that light attached to it.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         And the more the gravity pulls on you and light, the more time has to slow down so that light is always perceived as going at the same tick.

Fraser Cain:                Right. Right. Okay. So, now let’s put this all together. What if you are in a gravity well. Say you’re orbiting a black hole. And you’re also going very quickly compared to somebody who is going – I guess a black hole is a bad idea because you’ll be standing – but let’s say you’re on the earth. Right? I mean, but this is a practical example that we can actually do.

Dr. Pamela Gay:         Yes.

Fraser Cain:                Where you are on the surface of the earth.

Dr. Pamela Gay:         Yes.

Fraser Cain:                And so you’re in the presence of a gravity well.

Dr. Pamela Gay:         Yes.

Fraser Cain:                Or you’ve got your twin who’s flying in space on the International Space Station. They are in less of a gravity well because they’re at a higher orbit. But they’re moving faster.

Dr. Pamela Gay:         Yes. And to be fair, I haven’t redone these calculations in ages.

Fraser Cain:                Yeah, I haven’t either, and I apologize. Because it’s not in my head.

Dr. Pamela Gay:         So, last time I did these calculations, assuming I did them correctly – and I really hope I did. What I figured out was time goes more slowly for the astronaut, because the time dilation effect compared to being on the ground is greater for them. Because of the amount of acceleration that went into getting them where they are. Whereas, if you stopped them in space, this would cause them to fall to the earth. So, don’t do this.

Fraser Cain:                Right.

Dr. Pamela Gay:         And compared the time dilation due to their lesser pull from the center of the earth. But they’re still being pulled on, just less.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         But the dilation caused by the lesser pull at altitude compared to the surface of the planet – that time dilation due to gravity is a smaller effect than the time dilation due to accelerating so they don’t fall.

Fraser Cain:                And there’s gotta be like a perfect balance.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                Where you essentially experience no difference in time compared to the person who’s on the surface of the planet. Because your speed of movement balances perfectly out. The fact that they’re in a greater gravity well. And so you –

Dr. Pamela Gay:         And this would be a great homework problem.

Fraser Cain:                Yeah, there you go.

Dr. Pamela Gay:         And right now everyone is very glad I am not still teaching physics for engineers who get calculus.

Fraser Cain:                You would assign it.

Dr. Pamela Gay:         Because yeah…

Fraser Cain:                Yeah.

Dr. Pamela Gay:         You should be able to totally calculate out what density planet do you need? So, that someone on the surface and someone safely in orbit have the exact same ticking of the clock. Although, you can never sync those clocks. Because it takes time for light to get between the two points. But the ticks are the same duration tick.

Fraser Cain:                All right, so now I wanna blow peoples’ minds. And –

Dr. Pamela Gay:         I love time dilation. I just wanna say that –

Fraser Cain:                Yeah. Yeah. Yeah.

Dr. Pamela Gay:         – I absolutely love this concept.

Fraser Cain:                Yeah. Absolutely. And so, one very popular science fiction show that’s come out in the last little while is The Expanse. And they have these really powerful fusion rocket – Epstein rockets – that are able to take your spacecraft really, really fast. And so, if you could just jam on the engine and you had an unlimited fuel supply somehow. And you just kept accelerating, accelerating, accelerating …what would happen to time for you and the rest of the universe?

Dr. Pamela Gay:         Your time, by your perception, your heart would continue to beat the exact same way. But –

Fraser Cain:                You’d continue to be pressed into the seat at 1g.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                Right?

Dr. Pamela Gay:         Yeah. But the more your velocity increases …and here it’s the absolute value of it, that speed, the nonvector, scalar portion that matters. With each moment of acceleration, the moments that an outside observer sees you experience become fewer and fewer.

Fraser Cain:                Right.

Dr. Pamela Gay:         You will stop aging over time. You will stop breathing to the person watching because everything is slowed down so absolutely much. And in other science fiction series – I’m thinking of Hyperion here. There’s this wonderful example of in the future when high-speed travel between solar systems becomes practical. People of means can deposit their money and invest it in good things. And then skip through time become wealthier and wealthier. And experiencing less and less.

And I mean, imagine just how hard it would be on one hand to pop out of space travel and see all the amazing technological changes that have occurred. But at the same time be like, “And I’m rich now.”

Fraser Cain:                But the part that’s kinda crazy is that you could keep on accelerating and from your perspective you would never reach the speed of light. Because it’s impossible. But you would still be experiencing 1g of acceleration for days, months, years, decades.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                And even though, if you did the math, and you’re like, “I should have gotten faster than the speed of light.” You won’t and yet the distances that you’ll be traveling and the time that the rest of the universe will be experiencing just continue to grow.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                For as long as you can keep this going.

Dr. Pamela Gay:         And crazy things start to happen that we’ve discussed in other episodes many years ago. So, go digging through the archives. The way the equations for relativity work out is your momentum increases in ways that aren’t entirely linearly related to your mass. And the impact of this increase momentum, the faster and faster you go, is that it’s like you were gaining more and more mass.

Now, the reality is the number of atoms in your body will not change unless biological things occur. But your ability to destroy things if you hit them increases because of this apparent change in mass that is due to the relativistic effects on your momentum.

And this led to a question with which I broke a physicist and never really got a good answer. They sort of ended up walking away mumbling. And the question was if a body of mass goes fast enough so that its equivalent mass via momentum is such that it would be a black hole is it actually a black hole?

Fraser Cain:                Right.

Dr. Pamela Gay:         And the answer I’ve gotten from other theorists was no –

Fraser Cain:                No.

Dr. Pamela Gay:         – that’s crazy talk.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         But I did break one physicist –

Fraser Cain:                Good.

Dr. Pamela Gay:         – this way. I was proud of myself.

Fraser Cain:                So, the part that’s crazy is that if you could keep this acceleration up, you could be going to the point that in like a decade you would cross the Milky Way. In two decades you would go to Andromeda. In three decades you would be billions of lightyears away. And in about less than a human lifetime you would travel more than the distance to the edge of the observable universe.

Dr. Pamela Gay:         But the problem is the amount of energy that it takes –

Fraser Cain:                Of course.

Dr. Pamela Gay:         – to keep accelerating your –

Fraser Cain:                Yeah.

Dr. Pamela Gay:         – increasing effective mass. Not your actual mass increasing.

Fraser Cain:                Yes.

Dr. Pamela Gay:         Your effective mass increasing.

Fraser Cain:                Yeah.

Dr. Pamela Gay:         You would exceed the mass-energy of the universe before you exceeded the speed of light. Which is part of how we never actually go faster than the speed of light.

Fraser Cain:                Yeah. And so for someone watching you. You would just be very close to the speed of light. And you’d be doing that for billions of years.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                From your experience because you’re continuing to accelerate you would be like .999999% the speed of light. And so, it would take you two and a half million years to get to Andromeda. It would take you –

Dr. Pamela Gay:         Right.

Fraser Cain:                – 46 billion years to get to the edge of the –

Dr. Pamela Gay:         But you wouldn’t experience it.

Fraser Cain:                But you wouldn’t experience it. And yet the rest of the universe would. And so you would be – you would have to wait. You know, we’d have to wait 50 billion years for you to reach what was the edge of the observable universe. It’s absolutely mind-bending.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                And awesome. And it’s like this one hope that we can travel vast distances in a single human lifetime. Although, you have to say goodbye to everyone and everything you know.

Dr. Pamela Gay:         Well, just travel with your friends. Travel with your friends.

Fraser Cain:                That’s a good way to do it. All right. Thanks, Pamela.

Dr. Pamela Gay:         Thank you.

Fraser Cain:                Do you have some names for us this week?

Dr. Pamela Gay:         I do. I need to find the right window. I have so many monitors. I love my monitor fort.

Fraser Cain:                Your monitor fort.

Dr. Pamela Gay:         I have a monitor fort.

Fraser Cain:                Yeah. That’s awesome.

Dr. Pamela Gay:         This is what one should build – monitor forts.

Fraser Cain:                Yeah. Yeah. I love it. I’ve never heard it said that way, and I think it’s great.

Dr. Pamela Gay:         So, as always, we are here thanks to you. You out there, thank you. Thank you for supporting us and making everything we do possible. For allowing us to pay Rich, Allie, Beth, Nancy. All the people that keep Fraser and I on the straight and narrow. Because Lord knows we need herded. So, thank you for making this possible. Thank you for paying our server bills …our everything else. Thank you.

And this week in particular I would like to thank Kevin Parker, David Truog, Bill Nash, Helge Bjørkhaug, Richard Hendricks, Janelle Duncan. And it turns out that because it’s the end of the month, those are the only names I’ve got.

Fraser Cain:                Okay.

Dr. Pamela Gay:         So, thank you.

Fraser Cain:                Thanks, everybody. And thank you, Pamela. And we’ll see you next week.

Dr. Pamela Gay:         Buh-Bye, everyone.

Astronomy Cast is a joint product of Universe Today and The Planetary Science Institute. Astronomy Cast is released under a creative commons attribution license. So, love it, share it, and remix it. But, please, credit it to our hosts Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website astronomycast.com.

This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

Back to Top

This year’s Nobel Prize in Physics was awarded to three brilliant researchers who worked out some of the secrets of black holes. Today we’re going to talk about the chain of discoveries that led to this award.

Download MP3 | Show Notes | Transcript

NASA’s OSIRIS-REx Spacecraft Successfully Touches Asteroid (OSIRIS-REx) 

The Nobel Prize in Physics 2020 (Nobel Prize)

Roger Penrose (Nobel Prize) 

Penrose Triangle (Wolfram Mathworld) 

M.C. Escher (M.C. Escher Foundation) 

A Black Hole Primer with Chandra (Harvard) 

Who Is Stephen Hawking? (Science Alert) 

What Is Hawking Radiation? (Science Alert) 

What is the cosmic microwave background radiation? (Scientific American) 

The Nobel Prize in Physics 1978 (Nobel Prize)

Spacetime Curvature (ESA) 

The spin of the supermassive black hole in the Milky Way (Phys.org) 

What Is The General Theory of Relativity? (Science Alert)

Event Horizon (Swinburne University) 

Reinhard Genzel (Nobel Prize) 

Speckle Pattern (Wikipedia) 

Andrea Ghez (Nobel Prize) 

New Technology Telescope (ESO) 

W. M. Keck Observatory 

Zone of Avoidance (Swinburne University) 

Adaptive Optics (ESO)

Astrophotography Tutorial: Image Stacking in Photoshop (Astro Backyard) 

VIDEO: Simulation of the orbits of stars around the black hole at the centre of the Milky Way (ESO) 

Orbits and Kepler’s Laws (NASA) 

Event Horizon Telescope 

Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast, episode 583. The 2020 Nobel Prize in Physics. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pam, how are you doing?

Dr. Pamela:                 I’m doing well. How are you doing, Fraser?

Fraser:                         I am doing great. I’m sure all of you were just absolutely glued to the television just a couple of days ago, watching the OSIRIS-REx land. I know you did a big live stream of it.

Dr. Pamela:                 Yes.

Fraser:                         Absolutely amazing to see the sample collection.

Dr. Pamela:                 I am eagerly awaiting the spin maneuver, during which we’ll use the spacecraft’s moment of inertia –

Fraser:                         Yes.

Dr. Pamela:                 – to figure out how much material they vacuumed up. Then we know if they go and try to do this a second time, or if they just head on home.

Fraser:                         Yeah, yeah. Absolutely incredible. For people who, like you, watched it, you watched the simulation of what it was supposed to look like. Then later on you got this animation of it actually doing the capture, and it looked identical. Then suddenly there’s this big cloud of debris as the spacecraft is gathering the sample, and then popping back into space. It was absolutely amazing to see it, and just to think full circle that we were there to watch the rocket launch, and now we watched the sample get collected.

Dr. Pamela:                 Yes.

Fraser:                         Hopefully we’ll get a chance to watch it. They’re going to spin up the spacecraft, be able to detect the amount of material that’s collected into the spacecraft. Then from that point on, they’ll know whether they have to try again or whether they’re good to go, and they’re just going to be able to return home. Yeah, it’s pretty incredible.

Dr. Pamela:                 What is most amazing to me about this, just to add one more thing on this day of going sideways, they planned the mission so that when they went down to the surface, they’d be using their laser altimeter to figure out where they were relative to the surface. But this surface is such a boulder-strewn, rocky mess-

Fraser:                         Yep.

Dr. Pamela:                 That they instead had to do image matching on the way down. So, they completely changed how their navigation works, and it’s because they were making sure, “Okay, does what we’re looking at match what it should look like?”

Fraser:                         Yup.

Dr. Pamela:                 It looked just like the simulations.

Fraser:                         Yeah.

Dr. Pamela:                 They essentially recreated the simulations one image at a time.

Fraser:                         Yeah. It just shows the level of care that they went into to make sure that this went right. Yeah, absolutely stunning. All right. Let’s get onto this episode, which has absolutely nothing to do with OSIRIS-REx, but maybe we’ll be talking about that next week. This year’s Nobel Prize in Physics was awarded to three brilliant researchers who worked out some of the secrets of black holes. Today, we’re going to talk about the chain of discoveries that led to this award. Right, Pamela, where do you want to start with this year’s Nobel Prize?

Dr. Pamela:                 I think starting with Penrose is probably the best place to start.

Fraser:                         Okay. Let’s do it.

Dr. Pamela:                 The prize was split in half, and then in half again. The first half of it went to Roger Penrose, who I kind of adore as someone who thinks geometrically. This is somebody who figured out how to create what’s called the Penrose Triangle, which is a way of drawing a Escher-esque style triangle that can’t physically exist, but looks three-dimensional when you glance at it quickly. His work was actually inspired by Escher. Then he went on to figure out how to make staircases that are going both up and down simultaneously, and shared what he was doing with Escher, who then incorporated it into his art.

                                    It’s this amazing way of thinking multi-dimensionally that I think allowed Penrose to look at four-dimensional space-time in all of its crazy warpage, under the influence of relativity, and see his way through to being the first person to mathematically describe how black holes can exist. Einstein had seen in his math that black holes could be the fallout of what he had created, but declared them aphysical, not something that should exist.

Fraser:                         Right.

Dr. Pamela:                 Penrose came along and was like, “No, no, no, no. Okay. Here, let me change how we discuss the mathematics of this by using a topology argument,” and his paper that made it clear black holes can exist, that’s an awesome result, but what was much more powerful is he opened up a new way to discuss relativity through topology.

Fraser:                         I think it’s really interesting, when we report on various black hole discoveries and we talk about how Einstein was right again, as it relates to black holes, and with the event horizon telescope and things like that, the reality is that Einstein didn’t put a lot of thought into the implications of his theories as they related to black holes. As you say, he worked out in excruciating detail, the way time and space are intertwined, and acceleration, and how light and time should work near gravitational wells and so on.

Dr. Pamela:                 Yeah.

Fraser:                         But to practically think about the implications, and come up with this idea of black holes, with a lot of researchers after him who took that work and ran with it.

Dr. Pamela:                 Penrose is considered to have been the first and most important follow-on work to relativity, to have extended it in directions that essentially opened up a lot of the modern understanding we have of the universe. Now, the problem is that you can mathematically describe a black hole all day long, but until we can detect it, all it is is beautiful equations. Unlike string theory, this is actually beautiful. Penrose, along with Hawking and several others, have fallen prey to the “We did some really cool research, but it hasn’t been observed yet.” Unfortunately, Hawking passed away, but Penrose is still out there, still working as a faculty member out in Pennsylvania. So, he was still here to get a prize for work that he did before either of us were born.

Fraser:                         I wonder, if Hawking had lived, would he and Penrose have shared the Nobel Prize, and then it would have been shared with someone from the experimenter team? I wonder.

Dr. Pamela:                 I don’t think so, because Hawking’s work was on the evaporation of black holes, which this doesn’t speak to.

Fraser:                         No, that’s true.

Dr. Pamela:                 Hawking was actually– he worked as a student with Penrose at one point.

Fraser:                         Right, right.

Dr. Pamela:                 So, they were peers and collaborators, where Penrose was the senior collaborator.

Fraser:                         Yeah. Okay. Penrose, one of the names, one of the things, when I think about Penrose, I think about the Penrose Process, this idea that you could extract energy from a black hole. He has a lot of interesting ideas, a lot of way out there ideas. Some are theoretical; he has big opinions about the cyclical nature of the universe, which will get him into vociferous arguments with a lot of other cosmologists who deeply disagree with him.

Dr. Pamela:                 I’m okay with those arguments. Well, and this is the thing that makes the theorists in Nobel prizes, in some ways, so much more interesting. You see the same thing with the Nobel Prize that went to the original observation of the cosmic microwave background. The theorist kind of got left out to the side, but had done so much more interesting stuff. And here it was the observers that got the prize for noticing that the theory was right.

                                    With Penrose, I’m so grateful that they included him in this. And with what he did, he changed, fundamentally, how we look at black holes, initially, and then he took his topography modelings. He took what matters is the flow of space and time, more than the details of all the connections through that topography. And by changing how we look at things, just like Einstein changed our understanding of space-time by curving space, Penrose changed our ability to articulate that by saying, “Let’s look at the surface of that space-time and trace out the geodesics.” It was a revolution in thinking, and from that, we just kept seeing new and interesting things fall out.

                                    I love that what we’re seeing with both of these men, Einstein and Penrose, is that, by looking at the universe geometrically, it radically changes our understanding from simply working equations, which is what we teach kids to do in school. Imagine how much easier it would be to understand our universe if we, instead, looked at the flows of information instead of the equations of the information.

Fraser:                         Yeah, yeah. Geometry is one of those mathematics that I have a fondness for. I mean, when we learn geometry, even in Grade 8, and we start to see how you can make these calculations, the whole thing, as long as one part works, then you can work out, like a Sudoku puzzle, the rest of the angles in your series of triangles and shapes and all that kind of stuff and all of these ideas. And then, they extend into other dimensions and other kinds of shapes.

                                    And yet, at the end of the day, you’re working with shapes and topography. It’s kind of fascinating to think that even some of the most complicated objects in the universe, these black holes, which are spinning and twisting up space-time around them, still allow the exploration with the tools of geometry to figure out how they behave.

Dr. Pamela:                 And with the Penrose process, Penrose energy, what’s amazing is how this is fundamentally still getting used every day. This very week, we had a new article come out talking about how it’s been determined that our galaxy supermassive black hole can’t be rotating that quickly because it isn’t injecting energy into the orbiting stars around it.

                                    Our ability to figure out, we have a slow rotating black hole, through decades of literature, derives from this whole Penrose process. And so, this as physics is now so fundamental to everything we do that the release we looked at didn’t even relate it back to this. It related it just to relativity, it’s just part of relativity. And unfortunately, Einstein’s the only one who really gets credit for relativity.

Fraser:                         So, let’s talk about that idea of the Penrose process, just briefly, before we move on to the other parts of the Nobel prize.

Dr. Pamela:                 So, the basic idea is that, when you have a rotating black hole, it’s able to spin the space-time around it. And as that works, the spinning can get carried out outside of the event horizon of the black hole. And because this dragging of space-time extends beyond the event horizon, it essentially can insert energy into the universe around it. Now I have to admit, the way my brain conceives of it is that you simply have a continuum of – there’s a rotating black hole in the center, everything around it is twisting with space-time and somewhere within this continuum of space that’s twisting, is where the event horizon lands.

                                    It’s that twisting of space-time that makes such a mess of things, but also allows us, when we’re looking at accretion disks in other galaxies, when we’re looking at the orbits of stars in our own galaxy, to get at that rotation rate of the black hole that we otherwise could never get to. It also makes the math a whole lot uglier, even in graduate school. Most of the time when you’re doing the maths, they tell you to assume a non-rotating black hole because they show a small modicum of kindness.

Fraser:                         Right. All right, well, let’s move on from Penrose’s work on the theoretical implications of black holes, to the experimenters and observers that actually found them.

Dr. Pamela:                 And this is one of those things where I have to start by saying, I spoke quite highly of Reinhard Genzel as simply being a nice human, and most of the time he is. But right after I said that in our last podcast, he said something that I just want to call out as, “Dude, not cool.”

                                    So, Reinhard Genzel, along with Eckhart who was first author on the paper back in 1996, were the first to use speckle photometry. This is where you do extremely high-speed imaging and then you shift your images around on the bright spots in the image to line those up so that you can take out the effects of the atmosphere. He was the first person to use speckle imaging, to look at the center of our galaxy and identify the motions of the stars closest to the black hole.

                                    This paper came out in 1996. Andrea Ghez followed up as first author on the paper she put out in 1998. Genzel’s team was using the new technology telescope from the European Southern Observatory; Ghez was using the Keck telescope in Hawaii. Same kinds of measurements from both teams. And since ’96 to ’98, they’ve been both working in competing teams with Genzel taking leadership of his team, going back and forth, increasing our understanding of the supermassive black hole in the center of our galaxy. So, Genzel’s paper was first, he was not first author on it.

Fraser:                         Right, okay. So, let’s talk just briefly here about why these observations were so difficult. I mean, you talk about this idea of speckling, but I mean, the place they were looking is a place that one had not been able to look, and that’s the key.

Dr. Pamela:                 So, they were dealing with two major difficulties. The first is between us and Sag A star, that source of weird energy in the center of our galaxy in the constellation Sagittarius, between us and there is a whole lot of dust, a whole lot of gas, which makes it impossible to see all the way to the distance of the center of our galaxy using an optical telescope.

Fraser:                         Right. It is the zone of avoidance.

Dr. Pamela:                 Yeah, and something that is completely opaque and optical wavelengths can still be transparent in other wavelengths. In this case, they are using 2.2 micron infrared radiation to do their measurements. By shifting to the infrared, they were able to use longer wavelengths that are able to go all the way through that gas and dust. So, problem one was what color of light do you need to use to see into the center of the galaxy?

                                    Now problem two is our atmosphere is a noisy, moving thing, and light coming through our atmosphere is passing through pockets of variable temperature and other effects that cause that light to get refracted in variable ways as it travels that distance.

                                    To compensate for that, what we often do is we use adaptive optics, which works to tilt-tip different systems, flex different systems within the telescope to compensate for the motions of the atmosphere. That’s fairly new technology, it’s complicated technology, and it’s not always good-enough technology.

                                    The other way that we deal with this, and this is something even amateur astronomers do, is we take high-speed images where each image is capturing the light as it passes through the atmosphere for one way the atmosphere is. The next one, the atmosphere is slightly different. So, these two images will have moved relative to each other, but if you look at the brightest parts in both images, you can then line them up.

                                    So, in this case, you find one of the brighter stars, multiple of the brighter objects, within the image and you use that to line up all of these high-speed images. Then you can stack them and you can see things that you can’t see in any one image, but they are able to be seen in the cumulative stacked image.

Fraser:                         I’ll give just a quick analogy. When you look on the internet, you see beautiful pictures of Mars and Jupiter and Saturn that’s taken my amateurs and the way they do that is they point a video camera at a very bright object. This is the key, it has to be bright, and then they run the camera for an hour. Then they feed every single video frame into a piece of software that then combines all of the images together and goes, “Well, there’s a little part over to here that looks good, and a little part over there that looks good, and it just stacks and stacks and stacks.

                                    As long as it maintains the integrity of the data, you get an entire view of the planet as if there’s almost no atmosphere obscuring it from our point of view. It’s just because you’ve got a lot of data you can just keep matching, and the object was very bright. What makes this discovery so incredible is that viewing the stars at the center of the Milky Way in infrared, you do not have a bright object that you can look at.

Dr. Pamela:                 You have bright enough objects to line things up, but that’s as good as it gets. They have, literally, spent decades now watching the motions of these stars, tracing them out, trying to get all the three-dimensional motions fully understood, combining spectra where possible. They’ve built up a clear-cut case for the motions of these stars only being explainable with a black hole in the center of these stars’ motions.

                                    It’s always awesome to see two competing teams replicating each other’s work using different telescopes and getting the same answers and then each focusing in on different nuances.

Fraser:                         And that is nature. That is nature just telling you its secrets. That two people, similar technique, different telescope, different hemispheres, seeing the same thing and arriving at the same conclusion. Beautiful. That’s textbook. It’s what you want. Nobel prizes for everyone.

Dr. Pamela:                 Exactly. Exactly. Now, where this became a bit odd last week is Reinhard Genzel made a comment along the lines of he thinks that one of the reasons that they got the Nobel prize this year was because the committee wanted to make sure there was more diversity in the awardees and because Andrea Ghez had been working on this work, too, they both got the prize. He pointed out sometimes when he was the one who got a prize and she was not, and that’s just not cool, dude. You just got a Nobel Prize.

Fraser:                         Yeah. Just be gracious.

Dr. Pamela:                 Yes. I think he just had a poor moment. Don’t do that, dude. But these are two people that, in general, are very nice, kind, gracious people –

Fraser:                         Right, right.

Dr. Pamela:                 – and it’s excellent to see them awarded for their excellent work. This is not the first award either of them have gotten. They’ve kind of been working through getting all the prizes forever. Andrea gets– Actually, she was one of the people who got early career awards back in the ’90s when she was just starting her career. They did excellent work.

Fraser:                         You talked a bit about this idea that they used this technique to peer through the gas and dust of the Milky Way to observe the stars moving. What were they looking for?

Dr. Pamela:                 There were essentially looking to say, “Can we say the only object that can physically fit within the size of the orbits of these stars is a singular black hole?” Well, it had been hinted at, thought, hoped, drawn on overheads that there was a monster called a black hole lurking in the centers of quasars and other active galaxies. We didn’t have evidence of it through the ’90s.

                                    There were other arguments where people would say, “Well, maybe it’s a swarm of stellar mass black holes. Maybe it’s swarm of white dwarfs. Maybe it’s something else that we don’t even know.” This is why people drew monsters in the center of black holes. Everyone had their own favorite monster to draw on overhead sheets.

                                    With the work that Genzel and Ghez did, they were able to identify motions of stars that were getting Pluto-sized orbits around that super massive black hole. At that extremely small distance from the massive object, it became possible to say, “We can’t explain this as anything other than this amount of mass within this size radius, which seems to be consistent with a supermassive black hole, even though we can’t see within the event horizon”

Fraser:                         Right. It’s hard to do this as an audio podcast and I’m stumbling because when you see the animations, the 16 years of careful observations that they made, you see these stars buzzing around this missing spot in space – and I know we’ve talked about this before – but it is, if you had to watch one of the most stunning pieces of observational work, this is one of them that you just can see these stars moving like comets around nothing. And it can’t be nothing; it has to be gravity.

Dr. Pamela:                 And one of the things that really helped them early on, is there’s enough stars down near the center that they were able to catch one near its fastest point early on in this now couple decades long research program. And by catching stars at their closest point to the supermassive black hole, they’re able to get limits on both how big a thing could possibly fit in there, because clearly the stars [inaudible] [00:25:29] by is not inside of it. And just how massive does it has to be. And this is just good old standard Kepler’s motion, with relativistic corrections, of something goes fastest when it’s closest to the mass it’s orbiting. And so, they caught that; they caught that super-fast zip on by before going out to linger at greater distances, and now they’ve done it multiple times and it’s just cool.

Fraser:                         Yeah. And I think to finally – we’re still waiting for the photographs taken by the Event Horizon Telescope to bring the whole journey to home, that we will actually then see these interactions between the black hole, its event horizon, and the surrounding space, which has been predicted by Penrose. And that will complete that phase of the journey, to go from Einstein’s idea to Penrose’s detailed predictions of what should be seen, to actual observations, to powerful telescopes being able to actually reveal this region. It’s just textbook, it really is. This is Nobel Prizes. I’m so glad this was the Nobel Prize this year.

Dr. Pamela:                 And black holes have a history of saying, “Okay, Nobel Prize for each stage of the work.” We had Taylor who, in the past, got a Nobel Prize for his discovery of binary systems that were radiating gravitational energy, which was assumed to be via gravitational waves. This is just black holes, sometimes just keep revolutionizing how we see things and offering up more and more Nobel Prizes as they go.

Fraser:                         Incredible. All right, Pamela, do you have some names for us this week?

Dr. Pamela:                 I do and, as always, we are here thanks to the generous contributions of people like you. We have a bunch of really awesome humans that work with us, and we’d like to provide the medical benefits if they need it and pay them a good wage for the work they do, and you make that possible. You’re making the world better people; you’re making the world better.

Fraser:                         Thank you.

Dr. Pamela:                 So, this week I have a large list because we’re getting to the end of the month.

Fraser:                         Go fast!

Dr. Pamela:                 I will. I will. So, we have– I went to fast. We have Venkatesh Saree, Thomas Substrop, Joe Holstein, Sinai, SylvanBavesp, William Andrews, Jeff Collins, Harold Bragenhoggin, Ben Floss, StevenSheawater, MerrickVerdani, ArcticFox Nate Detweiler, Brian Gregory, MattRucker, Phillip Walker, Ron Thorson, Kevin Nika, Elod Avron, Dave Lackey, Karthik Vinkatromin, Cooper, GForce, Antesaura, Kay Koserif, Dean McDaniel, Paul D. Disney, Roland Vemerheim, Chris Shaw-Harford, Jason Graham, Father Praxor-Turnball, Donald E. Mundus. And we’re going to stop there.

Fraser:                         Thank you everybody.

Dr. Pamela:                 Thank you.

Recording:                  Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons Attribution license; so love it, share it and remix it, but please credit it to our hosts: Fraser Cain and Dr. Pamela Gay.

                                    You can get more information on today’s show topic on our website: astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

Relativity is used in more day to day situations than you may realize. In this episode, we will count (some of) the ways. This episode is brought to you live from the All-Stars Star Party in Indian Wells, California

In this episode we mentioned donations and tours. Click to learn more!

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

This episode is sponsored by: MagellanTV and Barkbox

Use Code – BPGC1V8IF8CMO to receive your first box! No credit card information necessary.  Gift Subscriptions do not auto renew. Can only be redeemed by US or Canadian residents. Cannot be combined or applied with any other promotion/offer. Cannot be applied to an already active subscription.

Bennu Mappers – Help CosmoQuest map rocks to help pick which ones OSIRIS-REx will bring back from asteroid Bennu! Start your coffee pots, get your favorite mouse/trackpads, & GET MAPPING! http://bennu.cosmoquest.org/

Theory of Relativity

What is a gravity well?

681: Gravity Wells from XKCD https://xkcd.com/681/

Gravity Well demonstration

Gravitational Redshift

4 Ways You Can Observe Relativity In Everyday Life

Einstein’s Relativity and Everyday Life

8 Ways You Can See Einstein’s Theory of Relativity in Real Life

Science Fiction or Fact: Is Time Travel Possible?

Twisted Physics: 7 Mind-Blowing Findings

Transcriptions provided by GMR Transcription Services

Pamela:                        Today’s episode of Astronomy cast is sponsored by Magellan TV. Claim your two-month free trial only available at Magellan TV dot com slash astronomy cast. Magellan TV is a brand-new streaming service that features the very best collection of space and science documentaries available anywhere.

                                    The service includes over 1500 documentary movies, series, and exclusive playlists designed with you in mind. Check out their space genre and explore the solar system like never before. If you’ve been listening to our last few episodes, you know that we’ve covered a mix of ethno-astronomy, discussing the sky stories of people around the world, as well as highlighting modern observatories that circle our globe.

                                    This mix of old and new reflects the content I’ve been consuming on Magellan TV. Where I can catch the latest news and archaeology, and anthropology, and also the most recent documentaries about our universe. This is a platform founded by filmmakers, that will help you gain insight into the things you are passionate about as you consume their productions, one awesome episode or film at a time.

                                    Find the answers to some of the biggest questions about the universe, and gain a deeper understanding about our solar system, astronomy, the cosmos, novas, and beyond. These are the stories of Magellan TV. Once again, claim your two-month free trial, only available at Magellan TV dot com slash astronomy cast.

Fraser:                         Astronomy cast episode 536. Everyday relativity. Welcome to astronomy cast. Your weekly fact-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of universe today, and with me, as always, is Dr. Pamela Gay. And I don’t have an introduction in front of me, so you are going to have to say your title.

Pamela:                        I am Dr. Pamela Gay. I am a senior scientist at the Planetary Science Institute, and the Director of Cosmoquest. And you should all be mapping boulders at bennu dot cosmoquest dot O-R-G.

Fraser:                         Man. Stop yelling at them.

Pamela:                        I really need them to map boulders and rocks and craters. Please?

Fraser:                         So, we are recording this episode live from Indian Wells, California, as part of the all stars party astro tour. We said that this episode of astronomy cast had ended. That we were going on hiatus. That was a lie. This is a bonus surprise. Enjoy. Maybe there will be more things. Who knows? This is going to be a weird summer.

                                    But you missed this one, unless you are here, but then listened afterwards. That is weird. But if you want to come on the next trip, I am going to be going to Iceland in January 2020. So, just go to astrotours dot C-O. They are taking reservations now until the middle of July. So, if you ever wanted to go aurora hunting with me, and also glacier hunting, and also Icelandic troll hunting, you should definitely go to astrotours dot C-O and sign up.

                                    We had a great time last time we went, and it was crazy storms. We didn’t see a lot of auroras, but I think this time it is really going to work. So, astrotours dot C-O, and sign up. All right.

                                    So, relativity is one of the most mind-bending concepts a human can attempt to contemplate. How can different places experience different speeds of time? Well, good news. You are taking advantage of it right now thanks to the handy gadgets like your phone. Pamela, you wanted to talk about some of the super weird ways that we actually incorporate relativity into our lives every single day. But before we get into some of that, let’s just talk about relativity. What is it?

Pamela:                        It is a set of theories most famously worked on by Einstein. Worked on actually by a whole bunch of people working together. And it describes, literally, our place in space and time relative to one another. And it turns out that even though we are so close, I am not seeing you right now, because it takes the photons of light bouncing off of your body a moment to reach me.

                                    And as I look out further and further, looking at people in successive rows, I am seeing them further and further back in time. And as those photons gravitationally interact with things around the universe, their paths get bent and distorted. And that gravity field, well, there is some weird stuff that happens. Because no matter who you are, no matter how fast you are going relative to something else, all of us see those photons moving at the exact same velocity.

Fraser:                         All right. So, let me just understand this for a second. So, I am moving – whatever – at 100 kilometers an hour. You’re moving 10,000 kilometers per hour. Someone is moving just a fraction away from the speed of light. And we are all watching a laser beam that has been shot from the International Space Station, and we are all watching that laser beam, and we are measuring the speed of light of that laser beam as it moves through space at the speed of light.

Even though we are all moving different distances. And I mean, I guess, in our everyday experiences, that is not what we experience with, say, a bullet being fired. If you are moving close to the speed of light, and I am moving at 100 kilometers per hour, we see a bullet moving at vastly different speeds.

Pamela:                        And just in more practical terms, when we are going down the highway, we see the cars that were passing moving relative to us at ten or fifteen miles per hour, unless you are a crazy person. But if you are standing on the side of the road, you see those cars going 60 to 90 miles per hour.

                                    And this difference in how we perceive velocities of cars, velocities of runners relative to our own motion, is not true with light. No matter who or what you are, light is going 300 kilometers per second, and that is the law.

Fraser:                         Right. So, this is, of course, the amazing discovery that Einstein made, and I am sure that someone could have thought of it earlier, because it is so weird, right? That time is the thing that changes.

Pamela:                        This episode is brought to you by Bark Box. For a free extra month of Bark Box, visit W-W-W dot Bark Box dot com slash astronomy. When you subscribe to a six- or twelve-month plan. As a lot of you know, I’ve got two dogs; Eddie and Stella. Eddie was my reason for getting Bark Box, and month after month he devoured the two large treats, played with the themed toys, and I would train him with the other made in America and in Canada tasty, healthy goodness that came packaged in every box.

                                    For years, Eddie loved on his Bark Box stuffed toys, and these high-quality playthings went through the wash after wash after wash and came out looking awesome. And then I got Stella. She is small, and she is mighty, and she likes to shred things. For her, there are extra heavy chewer toys. She actually managed to get one toy open, and its spiky ball core, well, it was like getting a whole new toy.

                                    I love Bark Box, and Stella and Eddie think your furry friends will love it too. Once again, for a free extra month of Bark Box, visit W-W-W dot Bark Box dot com slash astronomy, and get that box when you subscribe to a six- or twelve-month plan. Your furry friends will thank you.

Fraser:                         So, fine. And it is not like this hasn’t been proven a million times. Einstein is still right. So, then, what are the practical applications. How do we actually experience this? Are we experiencing time dilation as we are moving around in regular life?

Pamela:                        Yes. And where is starts to matter is once upon a time, we were worried about whether our pocket watches were closely enough aligned to keep the timetables of the trains in Europe.

But nowadays, when we are trying to get a satellite hook up to bring two news stations across the world together, we need to sync up those radio waves so that something that has a millimeter wavelength lines up on the other side of the world. And this requires more accuracy than your pocket watch is going to have.

Fraser:                         Yeah.

Pamela:                        And as we work out all these timings, we have to take into account the fact that where we are on the surface of the earth, we are experiencing a whole lot more gravity than the space signals are going off of. And this creates one sort of shifting light and shifting time.

                                    Those spacecrafts are moving at a different rate around the earth’s center than we are as the earth rotates. That creates another expansion of time.

Fraser:                         Okay. So, hold on. Those are two separate issues that maybe we should break up, right? So, there are two factors that will impact the amount of time that you experience. Gravity wells, and velocities. Can you explain that?

Pamela:                        So, with a gravity well, gravity is going I shall hold on to you. And the light, as it tries to get away, actually gets red shifted. As you look into a black hole, you see things getting redder and redder as it falls in. And part of this is doppler shifting, and red shifting, but gravity is also playing a role.

                                    As you pull out of the gravity well, that pull gets less, and light is getting affected less. Time is getting affected less. And so you have a difference due strictly to how far you are from the center of mass, and how fast your clock is ticking.

Fraser:                         Right. And the practical application for this – if you want a way to sort of think about it is think about the movie Interstellar, because they gave us this example. Spend some time near a supermassive black hole. Spend an hour, and you come back, and it has been 40 years for the people that you left back at home. And so, we, down here, on planet Earth, are experiencing less time than people who are out in space.

Pamela:                        If they are stationary.

Fraser:                         If they are not moving. Yeah. They are stationary. Yeah. Yeah. People who are out in space, relative to us. They are not moving, but they are just out there in space. They experience – woah. So, do we see them moving in slow motion? Do they see us moving in slow motion?

Pamela:                        They would see us moving in slow motion, but the catch is, you would fall out of orbit if you tried to do this. It would be very messy. Don’t do this.

Fraser:                         Right. So, just before they plummet to their death, they notice that we are moving ever so slightly a little slowly. That is weird, and then the screaming, and then the burning.

Pamela:                        And the death.

Fraser:                         Yeah. Okay. So, that is the one half of it, and then the other half of it is the velocity.

Pamela:                        And this is that twin paradox that they played with, with Scott and Mark, the two twin astronauts whereas Scott went around and around the earth, his velocity – he was accelerated to a higher rate of motion. And you look to see who did the acceleration to figure out whose time was shifted. You look to see who was accelerated. Scott was accelerated.

If he wasn’t, he would still be on the planet. This experiment wouldn’t have worked. He went at the higher velocity, and because he was moving faster, in order for him to see light traveling at the same rate, his clock has to slow down. The way I remember this is he was Buck Rogers in the 21st century but didn’t quite get there because he wasn’t going fast enough. Buck’s time slowed down, thus he made it.

Fraser:                         Right.

Pamela:                        So, the person who is on orbit, their clock slows down, they visit the future.

Fraser:                         So, then, is there some perfect balance point where – because the astronauts are moving at 28,000 kilometers per second. That is way faster than us. So, they are experiencing – so, we would see them moving in slow motion, but they are outside of our gravity well, and so then, they would see us moving in slow motion. So, is there some point where they balance out?

Pamela:                        Yes, but not with the earth, because we would fall out of orbit. If you go to something that has a greater mass, you can find that balancing point where the gravitational red shifting, and the time due to your velocity and acceleration, where those two counteract each other. Just not here, do that. There, we can’t get there yet, so maybe don’t do the experiment.

Fraser:                         Right. Right. And I know that when we look out to the other side of the entire universe – the very edge of the observable universe, that is as far as things can go. And those places have actually experienced 30,000 years of time different to us because they are moving away from each other. Like, time has no meaning.

Pamela:                        No. It doesn’t.

Fraser:                         Yeah. All right. So, then now your head is like come on. Prove it Fraser and Pamela. Fine. We are going to prove it. What are some of the practical applications how relativity has moved into our lives every day?

Pamela:                        Pokemon.

Fraser:                         Pokemon. I got to catch them all, but they are moving in slow motion.

Pamela:                        We are here when we could be out for the adventure day. And we are both Pokemon Go players.

Fraser:                         You are, like, a serious Pokemon guru. I mean, I dabble. You are hardcore.

Pamela:                        Right. I am.

Fraser:                         So, fine. Why could I not play Pokemon Go?

Pamela:                        No. Well, you could, but it wouldn’t know where you are, and you couldn’t catch them all.

Fraser:                         Right. You’ve got to grab that Pokestop right now.

Pamela:                        I’m totally spinning – I got a gift. I will send you a gift.

Fraser:                         Will you send it to me? Okay. Great.

Pamela:                        Yeah. Yeah. On wizards unite, I play that as well. I – Nayak, you are a problem in my life. So, these things that we do with augmented reality that paint our world with games, with information that rely on few meter accuracy and our position on the planet, all of these things have to take into account that we are latching on to three to five satellites that are high above our heads.

And if we weren’t latching onto those satellites, we wouldn’t have this accuracy. But those satellites are moving. And so, we have to do the relativistic corrections to the times, or we would be misplaced in time and space, and all of these things that are fun, informational, and prevent us from getting lost – Google maps. Thank you.

Fraser:                         Okay. So then, how does that work then? So, your phone knows what time it is? And how does relativity affect your phone?

Pamela:                        So, you latch on to three different satellites – or five – three to five satellites to get your position. If it is only two, you don’t know where you are. Your phone, your watch, whatever it is latches on to three different satellites that are zipping in slightly different directions, all have different light travel times to reach your phone, and your phone listens to the time the satellite sent the signal, compares the times for the three different signals, looks to see where the satellites thought they were when they sent the signal, does a relativistic correction.

                                    Using that relativistic correction, it goes the satellites, when they sent this signal, were actually these three places. I now know my separation to three different points, and with three points, you can figure out where you are in x, y, and z. Left, right, up, and down. So, you are literally drawing three measuring sticks between satellites and using relativistic corrections.

Fraser:                         Okay. So, your phone –

Pamela:                        Instantaneously.

Fraser:                         Your phone detects satellite one is moving towards you, and goes oh, you are moving towards me. So, time, you are moving in slow motion. Therefore, the time that you think you are sending the signal in not the time that I’m actually receiving the signal. I’m going to make an adjustment. But then that other satellite that is over there, that is moving perpendicular to me, is experiencing a different thing, and ultimately you are out of the gravity well, to a certain extent.

And it is calculating the velocities of all of these different – and the positions, and the directions it is going, and then it is accounting for that. And so, then, if you didn’t take Einstein’s equations into calculating your position on Earth, would GPS work at all?

Pamela:                        No. Not really. I mean, it would roughly tell you where you are.

Fraser:                         You’re on Earth.

Pamela:                        Yeah. And let’s not try. We know, because of Pokemon Go, relativistic equations make our lives at least a little more, well, wiggly.

Fraser:                         All right. Okay. So, fine. So, our phones, literally – I mean, for those of us who aren’t playing Pokemon Go – those of us who depend on, say, turn by turn driving directions, or hiking into the forest, again, you need your GPS to be accurate.

Pamela:                        Oh, yeah. Yeah. Yeah.

Fraser:                         Yeah. So, again, it is so funny. Like, you have a conversation with someone who is like I don’t believe Einstein. Like, fine. Then, throw away your phone. Give me your phone, actually, doesn’t believe in Einstein. I will take your phone, please. And we’ll go from there. All right. So, what else?

Pamela:                        Gold.

Fraser:                         Explain how.

Pamela:                        This is one of my favorites. So, if you’ve ever looked at the models they have of the lunar landers, there are a whole lot of shiny gold on that stuff. And this is fairly thin, fairly pure actual gold. And as it is sitting there, hanging out, going I am scattering mostly yellow light.

The reason that we see it the color that we see it, and part of the reason that it makes such a fabulous radioactive particle deterrent is that you have this extraordinarily dense atomic core, and this extraordinarily dense atomic core means that the photons that it interacts with, it preferentially shifts their colors as they interact down in the core, and we end up with less UV and blue light then we would if it didn’t have this dense core. And thus, more yellowy gold than we would without relativity.

Fraser:                         But how is it due to relativity?

Pamela:                        So, one of the awesome things about relativity is it talks about how light gets bent in these high density situations, and then you start getting into these affects of as you get in so close, everything is so dense that the physics goes out of norm. And if you try to use Newtonian physics to describe the motion, Newtonian is like no. Just, no.

I am going to misplace those photons and change the color. But with relativity, you can start to figure out how the momentum is changed of the photon. How the length has changed over the photon. All of these factors together, and gold, unless it has a lot of impurities, is going to give you a yellow refection.

Fraser:                         But I mean, it is not just gold, right? It is going to be any heavy element pounded into a thin film that has a lot of protons down thee in the core, right?

Pamela:                        And it gets even weirder when you start looking at things like Mercury. Mercury flows like a liquid, reflects like a mirror. And the way that it is able to do all of this is it was due to its super high-density core again. And so, with Mercury, again, super high-density core, super weird physics, super awesome material. So, anytime you broke a thermometer, and your teacher didn’t’ catch you fast enough, you played with the mercury?

                                    You were playing with relativity. You can say you experienced it while also experiencing a toxic substance. Don’t play with Mercury.

Fraser:                         Right. Right. But like, I’m just trying to imagine what the density of the material impacts the relativity, and the –

Pamela:                        So, think about a black hole is a high-density thing. It changes the physics we work with.

Fraser:                         Right. But isn’t that from the mass? Or is it from the density? Or, is that the same thing?

Pamela:                        Well, it is in many ways the same thing. You can have a star with ten solar masses of material, but it is not a black hole because the density is not such that you can get close enough to the sun. Yeah.

Fraser:                         Right. Right. Okay. I see. I see. So, it is the density that is actually doing the heavy lifting.

Pamela:                        Yes.

Fraser:                         Right.

Pamela:                        And there are other places that I did not realize that we have to make relativistic corrections until I started doing research to prep for this show. And one of those things that I made in school was an electromagnet. You wrap a whole bunch of wire around your fingers. You use your other hand to attach the wires to the battery.

                                    You don’t really shock yourself. Some of the electricity goes through your hand. Most of the electricity hopefully goes through the wire. And you can drag things around on the surface of your desk.

Fraser:                         With you hand?

Pamela:                        Yeah.

Fraser:                         Wait. Wait. Wait. Wait. Wait. You can – I’ve never done this. Like, I’ve coiled it around with a nail. Yeah. You take a nail, and you coil a copper wire around the nail, and then you attach the two sides to a battery, and you create an electromagnet. Congratulations. There is your science fair project. But you say you can do this with your hand? With your finger?

Pamela:                        So, you – it is just like you are winding up yarn, or cables, or something. You wrap the wire around your fingers. You have a loop of wire. You pull the loop of wire off of your fingers. You don’t keep the loop of wire on your fingers. You then grab a battery and hold the two ends of the wire on the battery. If you were in a cheap school, like the one I went to, and you don’t have battery cases, and you have an electromagnet, you don’t require the nail to make the electromagnet. You require the coils of wire.

Fraser:                         So, are you like a meat magnet?

Pamela:                        Yes. Yes.

Fraser:                         Neat. A magnet made of meat. All right. So, fine. Magnets. We are talking about electromagnets.

Pamela:                        We are talking about electromagnets.

Fraser:                         I’m intrigued.

Pamela:                        Now, if you have current running through a wire, moving charge generates a magnetic field. And if you have two wires next to each other, that have current – my arms can’t do that, for the people who are watching – if you have current with flowing in opposite directions in two parallel wires. You can get those wires to attract each other. You can get those wires to repel each other. And to really figure out how much of this is going on, you have to do relativistic equations.

Now, when we teach this to freshman in university, we leave those corrections out, because in the grand scheme of all the friction and everything else your standard electrical engineer is going to have to deal with, these are not a problem. But as we get into building faster and faster electronics, with more and more delicate wires – a super delicate wire that is getting yanked on by electromagnetism, well, you can wreck your circuit. So, you have to start worrying about these detailed effects.

Fraser:                         Right. But that was the force. Like, there was definitely a force that is applied to a wire, and same thing. You have a wire and you apply electricity through the wire, and it goes through the coil, and it will yank like a magnet. But I don’t understand where the relativity of this comes in. Is it that the –

Pamela:                        Electrons are moving close to the speed of light.

Fraser:                         Right. Okay. So, we’ve got something that is moving close to the speed of light, and you’ve got things going various directions in a computer at close to the speed of light. And in different, and in some cases moving from one spot to another spot, and when they move really close together, when you are looking at just a nanometer apart, they are interfering with each other, and experiencing time dilation and relativity.

Pamela:                        And it is in figuring out how strong the magnetic field is that you have to start to look at how fast the charge is moving. Any of us, if we are really bored, can put a natural magnet inside a coil, and reverse this experiment and generate electricity by shaking a tube with a magnet in it that goes through the wires. I am not going to do the hand gesture for that. And this generates current.

                                    Now, we are not moving the magnet that fast. The faster we move the magnet, though, the more current is created. The faster the current moves, the more magnetism is created. As we get current flowing faster, you have to take into account relativistic effects.

Fraser:                         So, would like really advanced – modern computers, they are taking that into account, right?

Pamela:                        Yes.

Fraser:                         And they are running at whatever clock rate that they are – the heartbeat of the computer – as it is performing it’s instructions, it is taking into account the relativistic accounts of all of those electron moving around inside the computer to make sure that as it is sending out instructions, and instructions are coming back with the answers, it needs to account for the time dilation for this.

Pamela:                        The manufacturers do all of that when they are building it.

Fraser:                         Yes. Of course. Of course.

Pamela:                        And then it is out of mine.

Fraser:                         Yeah. No. You don’t specifically have to deal with it.

Pamela:                        My processor isn’t worried about that. And it also becomes a problem when you are worrying about super conductors. And the faster we get things going, the faster we get our information from point a to point b, the more we have to worry about the corrections we need to make to what happened in the process of getting from point a to point b.

Fraser:                         That is amazing.

Pamela:                        And just in general, when you are firing an electron around, that electron is like hi. I’m going fast. Relativity matters. And old CRT televisions, they were firing electrons at the surface of that cathode. So, you have a ray of electrons –

Fraser:                         A beam.

Pamela:                        – going through a tube to hit a cathoid, otherwise known as a cat’s electric table – a heated table as far as I can tell – a cat. Cats like to sleep on CRT’s. Modern cats don’t have as much luck, and this is why they claim our keyboards.

Fraser:                         Right. Right. But so, like, an old television, you’ve got an electron beam. You’re one step away from your own large hadron collider there. You’ve got a particle accelerator in your house firing a beam of electrons in your general direction to entertain you.

Pamela:                        Yes. Getting stopped by that screen.

Fraser:                         By that screen. But you’ve got something that is moving at some dramatic percentage of the speed of light, and so you are going to have to take into account relativity.

Pamela:                        Especially when you are literally painting the screen with that beam using the magnets inside to direct the beam to vary the intensity so that you see different amounts of light, and different colors getting triggered in different places on your screen.

Fraser:                         I kind of imagine a cathode ray emitter is firing off these electrons, but it is accounting for the time dilation that each one of these particles is going to be receiving to make sure that it all comes together for us at exactly the right time. And if it didn’t make those kinds of modifications to the timing, television would suck.

Pamela:                        Yeah. And it all ended up in how they shaped the magnets was dictated by relativity. So, if, like me, you have an old cathode ray television in your basement because the garbage man won’t take it. And Goodwill won’t take it. And no one will take it.

Take it apart and look at the magnets. Look at the cathode ray. And the recent ones aren’t as fun as the ones that might be in grandparents’ basements or attics. But these were electrons going at 30% of the speed of light. And it matters.

Fraser:                         All right. Awesome.

Pamela:                        And other than that, we just have to look at things like the sun.

Fraser:                         Mm-hmm. Right. And we know that the sun is eight and a bit – eight minutes and 20 seconds away, or something like that. So, we are seeing the sun as it was eight minutes ago. That is fine.

Pamela:                        But more importantly, if relativity didn’t work, nuclear reactions wouldn’t work. Our sun would not have a power source.

Fraser:                         Right. Right. Fusion.

Pamela:                        And without a star, we would probably be dead.

Fraser:                         Okay. Fine. Right. But I will give you that. I appreciate my existence. Thanks sun. I apologize for all of the things I’ve said about you in the past. Your terrible heat. It’s okay. Okay. Fine. But how does fusion require relativity.

Pamela:                        This is the look of where do I start? That required ten years of university.

Fraser:                         Also, you’ve got three minutes.

Pamela:                        Yeah. That too. So, ah. Collisions of particles rely on relativity to dictate how things tunnel from a to b. Lower the energy barriers and allow the things that aren’t dictated by quantum mechanics to work. If it is not quantum mechanics, it is relativity that basically describes the sun.

Fraser:                         Perfect. I feel like I just got my degree. Ha ha. In your face education. All right. I think we’ve reached the end of the time we have here today. So, I think the point here that we should all really take away is thanks to Einstein. You were right again. And thanks to relativity, every day our lives are made better by the mind-bending concept of relativity.

Pamela:                        Go catch those pokemon and thank your GPS.

Fraser:                         Yeah. Nobel prize winning concept to help you catch pokemons. Did you have any names with you, or should we just generally thank all of our patrons? Thank you so much for this bonus thing.

Pamela:                        Yeah. So, I don’t have any names with me right now to read out. Now, we are going on hiatus. This doesn’t mean the work stops. We are going to be working to plan out our next year. Suzy is spending the summer going through and cleaning up our website, setting everything up.

And to thank all of you for kicking around, we are probably going to be sticking lots of bonus randomness into the feed, and we will be returning as we always do with dragoncon, and whatever Fraser is doing come September. It is changing for the summer, but we are not going away, and we would not be able to do what we do without all of the people who support us on Patreon dot com slash astronomy cast. You allow us to pay Suzy a livable wage for everything that she does.

Fraser:                         Thanks Suzy.

Pamela:                        Thank you Suzy. And she puts up with so much from the two of us. And thank you. I just kind of don’t know what to say.

Fraser:                         All right. Yeah. And we will see you on the – maybe not until         September. Or maybe, surprise, something else will happen.

Pamela:                        Surprise.

Fraser:                         All right. Thanks everybody.

Pamela:                        Bye bye.

Suzy:                           Thank you for listening to astronomy cast, a non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomy cast. You can email us at info at astronomy cast dot com. Tweet us at astronomy cast, like us on Facebook, and watch us on Youtube. We record our show live on Youtube every Friday at 3:00 PM eastern, 12:00 PM pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Surl. And the show was edited by Suzy Murph.

Interviewee:               

Interviewer:                

.

[End of Audio]

Duration: 36 minutes

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

Today, of course, we’re going to talk about the announcement from the Event Horizon Telescope and the first photograph of a black hole’s event horizon.

In this episode we mentioned donations and tours. Click to learn more!

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

This episode is sponsored by: 8th Light

Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. This long-sought image provides the strongest evidence to date for the existence of supermassive black holes and opens a new window onto the study of black holes, their event horizons, and gravity. Credit: Event Horizon Telescope Collaboration

The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun.

Fraser Cain:                 Astronomy Cast episode 526, the Event Horizon Telescope and the first imaged black hole. Welcome to Astronomy Cast, our weekly journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cane, publisher of Universe Today. With me as always Dr. Pamela Gay a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pamela, how’re you doing?

Pamela Gay:                I’m doing well. How are you on this “oh my God did he get to sleep” science week?

Fraser Cain:                 It has been the craziest week that I can remember in my recent space journalism history. Obviously the one that was all hands-on deck is going to be the topic for today, but the Beresheet Lander obviously crashed on the moon, which is sad. Our thoughts to all the people who worked on it and I really hope you take another crack at it. And of course, the successful launch of the Falcon Heavy, all three boosters landed successfully.

Pamela Gay:                It was amazing! It was amazing.

Fraser Cain:                 The coverage, the SpaceX coverage of the that whole mission was perfect except they lost the camera feed as the central booster was landing. And so, it was like, “Did it land? Did it land?” And then the – it cuts out and then you’re like, “I don’t know. And then it cuts back and there it is standing on – Of Course, I Still Love You. So, that was great. And apparently, they fished out the fairings from the ocean. And so, every part of this mission was full of win.

Pamela Gay:                And it is the most SpaceX thing, ever. That they lose video just as it gets to the barge. It’s like, that’s pretty much a given.

Fraser Cain:                 Yeah, it happens every time. Yeah, there’s something clearly – there’s something that happens as the rocket is coming in, it jiggles the camera, it freaks everything out and they lose that moment of footage. And then they come back and there it is. So, that’s the one thing, SpaceX if you’re listening, if you can tune that one thing up, that would be fantastic. Just let us be able to see when the thing lands.

Pamela Gay:                But we still love, Of Course, I Still Love You.

Fraser Cain:                 Yes. The such nerdy sci-fi named drone ship is so great. All right, today of course, we’re gonna talk about the announcement for the Event Horizon Telescope and the first photograph of a black hole’s event horizon. Pamela, this is a conversation that is two years in the making. It’s been April 2017 astronomers from around the world turned their radio telescopes towards the black holes at the heart of M87 and of course, the Milky Way. And took pictures of the black holes at the hearts of both of them. And this week, Tuesday, was it? Wednesday? Anyway, the 10th, two days ago, Wednesday, I’m so tired, we got that first picture announcement. So, where were you when you saw it?

Pamela Gay:                I was in the attic of my house livestreaming the event with our CosmoQuest community on twitch.tv/cosmoquestx, where you should all be watching and sharing live events.

Fraser Cain:                 Yes, live streams.

Pamela Gay:                And so, we were hanging out and watching it together and I don’t know about you, but I had this moment of, “Okay, so they got us with M87, in the beginning. And now we’re gonna have that Steve Jobs’ ending. There is more – but the thing was that never ever happened. And I don’t know about you but about 15 minutes into the press conference, I started getting nailed with press releases coming to us from Rick Fienberg and his fabulous press service at the AAS. And I’m flipping through them and I’m like, “Oh expletive, there aren’t going to be other images, this is it.” We only get M87.

Fraser Cain:                 Yeah.

Pamela Gay:                And I sat there, and I was like, “The science matches perfectly and I am sad because I wanted our Milky Way.”

Fraser Cain:                 Right? I know. I know, I was literally, I’m like, “This is great, where’s the Sag. A star?” Like, this was to be the consolation prize. The main event was – the first course was supposed to be the black hole at the heart of the Milky Way. And it’s funny, literally moments into this whole process, I started to dig and talk to all of my contacts, to try and figure out why. So, I do know probably, kind of why. Which is –

Pamela Gay:                So, let’s compare stories because I did the same thing.

Fraser Cain:                 Oh great! Okay, all right, so I’d heard two reasons. The first one is that essentially there’s a lot of dust in the Milky Way. We are inside the Milky Way with the supermassive black hole at the heart of the Milky Way. And so, that dust is a harder thing to tease out of the signal. And sort of the resolving distance of the Event Horizon Telescope sort of matched up in a way that made it a tougher image to gather.

But the second one that I love even more, is that the – is essentially that because Sagittarius A is a smaller black hole, it’s only 4.1 million times the mass of the sun. And matter is swirling around it so fast, it’s a much more dynamic environment. And so, they went with M87, because it is six billion times the mass of the sun. And so, the matter is swirling around it, at the speed of light, but it still takes days to go around. As opposed to minutes to go around. And so, they were able to – everything happened more in slow motion, they could test out their techniques, and then try them out on the supermassive black hole within the Milky Way. What did you hear?

Pamela Gay:                I heard that and then I also heard one more facet to that which is the angular size on the skies, the apparent size that the black holes appear, because they’re two different distances, means that Sag. A star isn’t really bigger even though it’s closer, because it’s a tiny little thing. And so, we don’t really get added detail on the part that’s luminous enough to see. Now, my personal hope is that because we’re seeing a faster moving system and we’re seeing a closer system where the luminosity of the innermost part of the accretion disk, we’re not seeing the black hole, we’re seeing the shadow of the black hole. My hope is that because that accretion disk is so much fainter, we’re gonna get to see other faint stuff around it that isn’t lost to the bright stuff.

So, even though the black hole shadow itself will appear probably about the same number of pixels in size, I’m hoping that there’s gonna be other stuff in the image as well.

Fraser Cain:                 Yeah, and the other kind of exciting thing is that because it is changing so dynamically, there could be a possibility that we might see like an animation.

Pamela Gay:                Exactly.

Fraser Cain:                 Right?

Pamela Gay:                Exactly.

Fraser Cain:                 We could see events unfolding over time to actually show what’s going on in this environment. So, it sounds like these two black holes, they are the biggest visually on the sky. They’re both some ludicrously small number 40 microarc-seconds or something like that. I’ve heard them say the size of a golf ball on the moon. The size of an orange on the moon, very small. But they are both roughly the same size, it’s just that the one M87 is 2000 times bigger and 2000 times farther than the one at the center of the Milky Way.

Pamela Gay:                And this is the kind of thing that all of us have come to understand, taking vacation photos when we fit the Eiffel Tower, I’ve never been to Paris, but when other people fit the Eiffel Tower in the palm of their hand, you just switch up what’s closer and what’s farther and suddenly the smaller thing appears larger. Or, in the case of the moon and the sun, the moon and the sun are two very different sizes, but they appear the same angular size in the sky.

In the case of these two black holes, it’s the same kind of effect. They appear roughly the same angular size in the sky even though their physical sizes are radically different.

Fraser Cain:                 Now, did you follow the logistics of what it took to make this image at all?

Pamela Gay:                I’ve followed some of it, I have to admit that I squeaked with joy when they showed pictures of Haystack Observatory, which is where one of the correlation facilities is, because that’s in my hometown. And the first place I ever worked as an astronomer and earned money for doing astronomy. So, Haystack Observatory a radio facility up in Westford, Massachusetts, my hometown, is one of the places where they worked to combine all the data as well as the Max Planck Institutes.

And the bulk of this correlation of all of the data was done by Dr. Katie Bouman, and there are some amazing pictures floating around the Internet where they have racks of hard drives that contained all of the data that she worked on developing algorithms to combine all that data to get what we see. It is 5 petabytes of data, which will seem small once the Large Synoptic Survey Telescope exists. But today, seems like an amazing amount of data.

Fraser Cain:                 So, there eight separate telescope facilities around the world, several in North America, two in South America, a couple in Europe, one in Greenland, and one in Antarctica. And so, for a week, around April 2017, all these telescopes, everyday turned on the same objects in the sky and recorded their data to these hard drives. And then all of these hard drives were moved together to those facilities, as you mentioned, for further data processing. And actually, it was four separate groups that worked on, independently to produce their own separate images. And then they met and compared their results and saw that they all got the same thing. So, they sort of did peer review all at the same time.

And then, as you said, Dr. Bouman, was the one who did the final – had developed the algorithm that would combine it all into the final image that we all saw.

Pamela Gay:                And what I loved is to me, it sounded so much like solving a problem set back in graduate school. Where you have all of this complicated steps and stuff and things that all have to get brought together in the exact right way or your final result is off in the fifth digit. And seeing how all these different institutions worked their way through all of these different problems, and then did like you do when you’re doing a problem set and it’s like, “Okay everyone, I got this number, what did you get?” And it’s that consensus of, “Oh wow! Most of us typed in the numbers the right way and all got the same answer.” That is the “Yes! We did this right,” verification.

Science is a matter of did you type it all in correctly. And in this case, did you write the software bug-free in the same way? And it’s awesome to watch.

Fraser Cain:                 So, let’s assume that people have seen the picture or have the picture in front of them. When you look at this image, what are you seeing?

Pamela Gay:                So, I personally see an angry clown smile, but that’s me.

Fraser Cain:                 Sure, yeah, I mean, there is definitely a group that is thinking that it is the Angry Clown’s Imaging Telescope, but what are the features that are in this image?

Pamela Gay:                Right. So, you have a very circular central dark shadow, that is surrounded by an orange ring that is brighter in the lower regions in a slightly asymmetrical way that is what reminds me of an angry clown smile. So, you can imagine clown smile, that is the shape of the overly bright region.

Fraser Cain:                 I definitely see it. And can now never un-see it.

Pamela Gay:                Thank you. I don’t know what that’s called when you share an image instead of a song and create a brain worm, but I think we have mastered it.

Fraser Cain:                 Yep.

Pamela Gay:                So, those brighter areas down in the bottom section of this image, that is where the material is coming towards the observer and you’re seeing a brightening and the source. The fainter area you don’t have that Doppler shifting going on, so you don’t have that added light. And what we’re seeing is not the black hole, this is one of those things that has really annoyed me about the coverage. What we are seeing is the light from the accretion disk. And the shadow of the black hole on that bright material. And this material is running at a right angle, it’s running perpendicular to the amazing jets that we can see in the Hubble images of M87 and that continue to stretch away from the galaxy in larger field of view radio images.

Fraser Cain:                 And so, I think that the features that are really spectacular here, is we see that central – now, you know, it is not the black hole, but the black hole’s in there. That is essentially the event horizon, the part where the light is now trapped forever, and all the matter and all the light is trapped. And around that, the donut, is this material that is swirling around, this accretion disk, and as you said, it’s bright on one side, because it’s coming towards us. And it’s dimmer on the other side because it’s moving away from us, and literally the light is getting red-shifted in brightness so that we can see more and less of it.

In fact, some of the light that you’re seeing has actually happened on the other side of the black hole. And it is being pulled around by the gravity of the black hole, so that you can see it. That’s how tangled up space/time is going on here.

Pamela Gay:                And what is really amazing about this is this image is Pluto orbit scales. We are looking at a region that is 0.0019 of a light-year. So, this is the kind of thing that light-days across, not light-years, light-days across. These are scales we can start to actually imagine and think about.

And when we think about M87 in general, we’re looking at these beautiful images of this large cotton ball of a galaxy. And that large cotton ball of a galaxy, is actually bigger than our own galaxy, and is 32,000 parsecs across.

Fraser Cain:                 Right. Now, let’s talk a bit about the wavelengths that went into this, because you’re seeing a lot of people out there on the Internet, and I think you’re the – you’re being very careful to say, “It’s not a photograph of a black hole.” I’m not being so careful, because it’s in there. There’s a black hole in there, we’re seeing it. But it is an image in radio waves, not in visible light. So, why is that important?

Pamela Gay:                Well, it’s important because, the black hole itself, we don’t know how big it is. What we’re seeing is the edge of the event horizon. This was written in a way that is so good, I’m gonna quote it. It was written by Grant Tremblay, who goes by @astrogrant, and he was reacting to the fact that many people have been like, “Well, why didn’t they look at it in the optical? This is just a fuzzy image.” Because people don’t understand the sense of scale on this. And what he wrote was, “I’m sorry that the image, whose earth-sized baselines yielding a 20 milli-arcsecond beam – ” Beams is how we discuss radio-astronomy, “– yielding a 20 milli-arcsecond beam resolving five short shield radii, whose deconvolution placed 10 resolution elements over a 50 light-day black hole shadow and photon ring. In an object 55- million light-years away was too blurry for you.”

Fraser Cain:                 Yeah.

Pamela Gay:                And it’s when you start to realize, we’re looking at a ring of light that is getting bent toward us by a black hole’s event horizon 55 million light-years away. That’s kind of freaking awesome!

Fraser Cain:                 Yeah. Yeah. And, I mean, the whole reason that they went with radio waves, like if they could have taken a visible light picture of this region, they would have done it.

Pamela Gay:                But we don’t have the tech.

Fraser Cain:                 We don’t have the technology to do it. The only way that you can make a telescope the size of the earth, which is what they did, is to take it in radio waves. So, you are seeing the radio emissions of the region around the black hole. That’s probably not the most energetic part. It’s probably the best picture would probably be an x-ray or a gamma ray telescope looking at that region. Right? Visible light would definitely show you all kinds of cool swirling stuff, infrared, ultraviolet, would be amazing in every wavelength; but radio is the one they could.

Pamela Gay:                And the reason for this is, with radio receivers, we have the ability to go, “There’s a wave front. There’s a wave front. There’s a wave front.” As the individual waves get to the planet Earth. And we have to align the data, so that when we correlate it you have the arriving wavelengths that hit each telescope lined up such that you’re sampling the same wave front. This means they have to take into consideration the shape of the planet which is determining the difference in distance for each telescope from the source. And even though its 55 million light-years away, that matters.

Fraser Cain:                 Yeah.

Pamela Gay:                And then they have to take into account that our silly planet has this nasty habit of rotating and that constantly changes the distance. And because our planet isn’t perfectly round, it changes it in constant ways that have to be re-calculated for each of the facilities, and this is hard.

Fraser Cain:                 Yeah.

Pamela Gay:                And there were space-based telescopes working in different wavelengths that got in on understanding the science on this. So, if you watch the press conference, they highlighted some of the missions that were included in the scientific studies that took place. But they didn’t use correlators to try and tie in radio data that was taken from space. And I got to thinking about this and it’s really hard to take into account the fact that our planet, which isn’t perfectly round rotates and we have to calculate how the distances change over time. Well, spacecraft orbit really fast and trying to correlate that in would have just been an additional special form of nightmare.

Fraser Cain:                 Yeah.

Pamela Cain:               But what we did, I think the best word for me to describe this was this was a deeply satisfying piece of science. This is that feeling you get when you solve the stupid hard puzzle that required you to find the three pieces the cat stole and put in different places in the house. And you succeed in finding them the missing pieces and everything fits, and it exactly matches the box. And you figured it would exactly match the box but it’s just nice when that happens.

Fraser Cain:                 Like again, the wavelength that they did this at is 1.3 millimeters. And so, they had to align the wave fronts from all of these telescopes. And, as you said, the planet is rotating. Some of these places, they are moving towards the object and then they’re moving away from the object as the earth is turning. As the earth is going around its orbit around the solar system, you’ve gotta line up all of these images that you take, all this data that you capture have to be lined up to the 1.3 millimeter. And otherwise, you aren’t taking a picture with a telescope the size of the earth. You’re taking a telescope with one additional little radio dish. It’s a mind -bending accomplishment requiring as much computing power, as much computing thought as the underlying astronomy and physics. It’s incredible.

Pamela Gay:                And I haven’t read the how they completed the image paper in detail, so I don’t know if this is mentioned in it, but with pulsar science they actually have to take in some accounts the tides of the planet into account to get proper measurements. Which means sometimes you have to not just take into account the fact that our planet is rotating, but you have to take into account that the height of mountains varies as the moon passes overhead. We don’t think about how our own earth is flexing with the moon’s orbit and that can muck up pulsar timings.

Fraser Cain:                 Yeah.

Pamela Gay:                So, these are all the crazy amazing things you have to take into consideration. And we’ve done things like that before but on different scales with VLBA and VLBI and all the other very long baseline add-on the fourth word as you will. But this was a new and fabulous implementation of the system.

Fraser Cain:                 Amazing. Amazing. So, we’re probably going to be digesting this for years, and, of course, we’re waiting for the Sagittarius A star image as well. But putting this in context, you were talking a bit before about how small this image is in comparison to what say the Hubble Space Telescope could do.

Pamela Gay:                So, we have – many of us have fallen in love with this object, because it has been studied across so many different wavelengths creating fabulous dynamic images. We’ve been able to watch over time seeing the knots of plasma move in the jet of M87. This is a fabulously dynamic system. And it’s easy to lose the context of this black hole in all that data, because it is so small that it’s almost inconceivable.

So, let’s work our way outwards. The black hole image, not the black hole itself, the image that we’re seeing, the radius of that beautiful photon ring, is a couple of percent of the size of a pixel on the Hubble image.

Fraser Cain:                 Right. So, the Hubble Space Telescope with an enormous CCD with one of the most sensitive lenses and instruments out there, one of its pixels it is what fraction of it?

Pamela Gay:                It’s about 2% is as near as I can tell. I need to math this out, but that’s about what I’m getting at.

Fraser Cain:                 Right.

Pamela Gay:                So, you have this little tiny region, now the short shield radius of this black hole that we’re looking at it is 0.0059 parsecs across. Now, that short shield radius is what is in the very core. Expand out a factor of 1000 and you have at 0.12 parsecs, that’s the size of the accretion disk around the black hole. So, we’ve already gone a factor of 1000 and we’re still now a couple of pixels across in that Hubble image. Now when you look at this Hubble image, there’s these beautiful – well a beautiful purply jet superimposed on the main blob of this blobular, elliptical galaxy. And that purply blob that we’re seeing is a plasma jet associated with the jets of material streaming out of this accretion disk. That plasma jet is 1.5 kiloparsecs, we’re now a factor of 10,000 larger than where we were a moment ago. And that’s the inner purply jet.

Now keep going and we get to the radius of the galaxy itself which for the main star bulge part, not the full envelope the main star bulge part is what I’m talking about, that’s 32 kiloparsecs. We then have the radio jets, those are 40 kiloparsecs. The extended halo around this elliptical galaxy is 150 kiloparsecs. And all of this is embedded inside of the Virgo cluster where M87 is the second brightest galaxy. And the Virgo cluster itself, with its more than 1500 galaxies, it is 2.2 megaparsecs in radius.

So, when we’re used to looking at these beautiful Hubble images of the Virgo cluster and then zooming in on M87 and then zooming in on that plasma jet, we’re still orders and orders of magnitude larger than what they were able to see with the Event Horizon Telescope. And I can see the Virgo cluster in a backyard telescope, I can just make out M87, it’s a Messier object. We’ve known about it for a while, you don’t need a good telescope, you just need dark skies. You can see M87 in your backyard. But down smaller than the eye can behold, and most brains can imagine, that’s what this team was able to image.

Fraser Cain:                 Absolutely incredible. What comes next do you think? I mean obviously we may have to have this conversation again when they release the image of Sagittarius A star in the Milky Way.

Pamela Gay:                I think right now comes a whole of people sort of going, “Well huh. It exactly matched relativity. That is a thing.”

Fraser Cain:                 Uh-huh, Einstein right again, although he didn’t like the idea of black holes. But his calculations like the ideas of black holes, therefore Einstein was right even though he would prefer to not be right in this situation.

Pamela Gay:                And all the folks that predicted black holes that Einstein didn’t initially believe until his math forced him to believe it, they were all right. And this is just satisfying, and I think it’s going to lead to a lot more confidence in our development of computer models of how does all the physics tie together across all the different scales for active galaxies like M87. We’re going to start to say, “Yes, we have confirmed this about the black hole’s accretion disk. We have confirmed this about the photon ring. We have matched the inner most scale.” And now let’s build out and just explain all the physics on all the scales and that is beautiful.

Fraser Cain:                 I really think like when you see some of the research papers out there that are making fairly bold predictions or even very conclusive results about things, it’s on whiffs of data that they’re able to get the spectroscopy to this level of tolerance from this one active galactic nuclei that tells them that this chemical is present and whatever, right?

Pamela Gay:                X-ray and gamma ray astronomers count their photons and some of them even name their photons.

Fraser Cain:                 Right. So, this actually, when you see this blob with bright spots and faint spots, and there’s a ton of underlying data that you don’t see in the picture that astronomers have access to. It really does feel like they’ve got mountains to work with and use for their theories of black holes and relativity and accretion disks and jets and all these things. They’re gonna be busy.

Pamela Gay:                Ten resolution elements across the short shield radii. Ten resolution elements which is a fancy radio astronomy way of saying not quite 10 pixels but something, somewhat similar to that. That’s the best analogy I can come up with right now. That’s pretty good. That’s pretty good. We’ve all zoomed in on images until we were looking at a face that was only that many pixels apart.

Fraser Cain:                 Yeah. Yeah. Amazing. Amazing. Well, congratulations to everyone on the Event Horizon team, 200 scientists, eight observatories, two years of work and we couldn’t be happier with the results.

Pamela, before we go, do we have some names this week?

Pamela Gay:                We have names because our audience is fabulous. So, to thank our Patreons for April, I want to say thank you to Jordan Young, Burry Gowen, John Jogerst, Andrew Poelstra, David Truog, Brian Cagle, TheGiantNothing, Ramji Enamuthu, Robert Palsma, Corey Devali, Jos Cunningham, Emily Patterson, Dana Norey, Joseph Hoy, Kjartan Saevre, Helge Bjorkhaug, I’m sorry, I adore you, your name is hard, Bill Hamilton, Frank Tippin, Richard Rivera, Greg Thorwald, Les Howard, Thomas Sepstrup, Laura Kittleson, Silvan Wespi, Jeff Collins, Marek Vydarney, John Drake, Nate Detwiler, James Platt, Elad Avron, Phillip Walker, and I’m gonna stop there and we will get to the rest of you next week. Thank you, you are what allow us to pay Susie, keep the servers going and keep bringing you this science, thank you. We are enabled by you.

Fraser Cain:                 Thank you. And thank you Pamela, we’ll see you all next week.

Pamela Gay:                Bye-bye everyone.

Speaker 1:                   This episode of Astronomy Cast is brought to you by 8th Light Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember, that’s www.8thlight.com. Drop them a note. 8th Light, software is their craft.

Speaker 2:                   Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at [email protected]. Tweet us at @astronomycast, like us on Facebook, and watch us on YouTube. We record our show live on YouTape every Friday at 3PM Eastern, 12PM Pacific or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Sorrel and the show was edited by Susie Murph.

[End of Audio]

Duration: 35 minutes

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download