The Basics

STUDY FINDS THAT CAVITIES SCULPTED BY STELLAR OUTFLOWS DID NOT EXPAND OVER TIME

Stars aren't shy about announcing their births. As they are born from the collapse of giant clouds of hydrogen gas and begin to grow, they launch hurricane-like winds and spinning, lawn-sprinkler-style jets shooting off in opposite directions.

This action carves out huge cavities in the giant gas clouds. Astronomers thought these stellar temper tantrums would eventually clear out the surrounding gas cloud, halting the star's growth. But in a comprehensive analysis of 304 fledgling stars in the Orion Complex, the nearest major star-forming region to Earth, researchers discovered that gas-clearing by a star's outflow may not be as important in determining its final mass as conventional theories suggest. Their study was based on previously collected data from NASA's Hubble and Spitzer space telescopes and the European Space Agency's Herschel Space Telescope.

The study leaves astronomers still wondering why star formation is so inefficient. Only 30% of a hydrogen gas cloud's initial mass winds up as a newborn star.

Though our galaxy is an immense city of at least 200 billion stars, the details of how they formed remain largely cloaked in mystery.

Scientists know that stars form from the collapse of huge hydrogen clouds that are squeezed under gravity to the point where nuclear fusion ignites. But only about 30 percent of the cloud's initial mass winds up as a newborn star. Where does the rest of the hydrogen go during such a terribly inefficient process?

It has been assumed that a newly forming star blows off a lot of hot gas through light-saber-shaped outflowing jets and hurricane-like winds launched from the encircling disk by powerful magnetic fields. These fireworks should squelch further growth of the central star. But a new, comprehensive Hubble survey shows that this most common explanation doesn't seem to work, leaving astronomers puzzled.

Researchers used data previously collected from NASA's Hubble and Spitzer space telescopes and the European Space Agency's Herschel Space Telescope to analyze 304 developing stars, called protostars, in the Orion Complex, the nearest major star-forming region to Earth. (Spitzer and Herschel are no longer operational.)

In this largest-ever survey of nascent stars to date, researchers are finding that gas — clearing by a star's outflow may not be as important in determining its final mass as conventional theories suggest. The researchers' goal was to determine whether stellar outflows halt the infall of gas onto a star and stop it from growing.

Instead, they found that the cavities in the surrounding gas cloud sculpted by a forming star's outflow did not grow regularly as they matured, as theories propose.

"In one stellar formation model, if you start out with a small cavity, as the protostar rapidly becomes more evolved, its outflow creates an ever-larger cavity until the surrounding gas is eventually blown away, leaving an isolated star," explained lead researcher Nolan Habel of the University of Toledo in Ohio.

"Our observations indicate there is no progressive growth that we can find, so the cavities are not growing until they push out all of the mass in the cloud. So, there must be some other process going on that gets rid of the gas that doesn't end up in the star."

The team's results will appear in an upcoming issue of The Astrophysical Journal.

CREDITS:

NASA, ESA, and N. Habel and S. T. Megeath (University of Toledo)

Four hundred thousand years after the big bang, the universe was a cold, dark fog of hydrogen and helium atoms. Less than 400 million years later, it had begun to shine with the light of infant galaxies. Sometime in between, the first stars must have formed.

What were these stars made of? How big and bright were they? How long did they live, and what happened to them when they died? Do any still exist?

The fact is, no one really knows exactly what the first stars were like. Not even the most powerful telescopes operating today—space telescopes like Hubble, Spitzer, and Chandra, and ground-based telescopes like Keck and ALMA—have been able to detect them. But we do have some ideas.

Credit: NASA/STScI

It is just one of billions of galaxies, but the Milky Way is our galaxy, our home in the universe.

Our first observations of stars, beginning with the naked eye and then with successively more powerful telescopes, happened here, providing a baseline for all the discoveries—and new questions—to follow.

One major question astronomers investigate when studying galaxies is how stars form within them. The James Webb Space Telescope’s powerful infrared instruments will improve our understanding of all stages of the star “lifecycle”—from birth to death and back again, to the rise of the next stellar generation. Astronomers know that stars form out of collapsing clouds of gas and dust, but they don’t yet know the exact sequence of how stars are born. What triggers a gas cloud to collapse? How much of that “mother” cloud does a star use up when it forms? How and when do planets begin to form around a new star?

At the end of their so-called lifecycle, stars “die” in a variety of dramatic and scientifically interesting ways—from gentle exhales of material to violent supernova explosions that expel stellar shrapnel into the galaxy. Many dying stars and stellar corpses are embedded in their ejected material; this shrouds them from view in visible light, but Webb’s infrared vision penetrates the dusty haze. Webb will help us probe and understand both this residual material and the former star. It allows astronomers to test their theories for how stars burn out, and how the heavier elements forged within these stars are recycled into the galactic environment to help create the next generation of stars.

Webb will help us get a better grip on how many stars there are in the Milky Way and how those stars are distributed throughout the galaxy. The most common stars in the Milky Way are “dwarf stars” that are too dim for the Hubble Space Telescope to observe well in visible light, but that are easily visible in the infrared wavelengths that Webb can detect. Knowing how many dwarf stars there are, as well as other types of stars, also tells us how quickly or efficiently stars formed at various stages in the galaxy’s history. This will give astronomers a much more informed local baseline from which to compare and contrast other galaxies.

Credit: NASA/STScI

How dark is the sky, and what does that tell us about the number of galaxies in the visible universe? Astronomers can estimate the total number of galaxies by counting everything visible in a Hubble deep field and then multiplying them by the total area of the sky. But other galaxies are too faint and distant to directly detect. Yet while we can’t count them, their light suffuses space with a feeble glow.

To measure that glow, astronomers have to escape the inner solar system and its light pollution, caused by sunlight reflecting off dust. A team of scientists has used observations by NASA’s New Horizons mission to Pluto and the Kuiper Belt to determine the brightness of this cosmic optical background. Their result sets an upper limit to the starlight emitted by faint, unresolved galaxies, showing that there is about twice as much optical light permeating space as can be accounted for by all known galaxies.

Credit: NASA/STScI

On March 14, NASA will join people across the U.S. as they celebrate an icon of nerd culture: the number pi. So well known and beloved is pi, also written π or 3.14, that it has a national holiday named in its honor. And it’s not just for mathematicians and rocket scientists. National Pi Day is widely celebrated among students, teachers, and science fans, too. Read on to find out what makes pi so special, how it’s used to explore space, and how you can join the celebration with resources from NASA.

2—How much pi do you need?

3—Officially official.

4—Pi helps us explore space!

5—Not just for rocket scientists.

6—Teachers rejoice.

7—How does NASA celebrate?

8—A pop-culture icon.

9—A numbers game.

10—Time to throw in the tau?

Black holes are mystifying yet terrifying cosmic phenomena. Unfortunately, people have a lot of ideas about them that are more science fiction than science. Black holes are not cosmic vacuum cleaners, sucking up anything and everything nearby. But there are a few ways Hollywood has vastly underestimated how absolutely horrid black holes really are.

Black holes are superdense objects with a gravitational pull so strong that not even light can escape them. Scientists have overwhelming evidence for two types of black holes, stellar and supermassive, and see hints of an in-between size that’s more elusive. A black hole’s type depends on its mass (a stellar black hole is five to 30 times the mass of the Sun, while a supermassive black hole is 100,000 to billions of times the mass of the Sun), and can determine where we’re most likely to find them and how they formed.

1. 100% Chance for Cosmic Winds

“Space weather” describes the changing conditions in space caused by stellar activity. Solar eruptions produce intense radiation and clouds of charged particles that sweep through our planetary system and can affect technology we rely on, damaging satellites and even causing electrical blackouts. Thankfully, Earth’s atmosphere and magnetic field protect us from most of the storms produced by the Sun.

2. Hello? Can You Still Hear Us?

We launched the Parker Solar Probe to learn more about the Sun. If you lived on a world around a supermassive black hole, you'd probably want to study it too. But it would be a lot more challenging!

You’d have to launch satellites that could withstand the extreme space weather. And then there would be major communication issues — a time-delay in messages sent between the spacecraft and your planet.

3. Can Someone Turn Off the Lights?

Supermassive black holes at the centers of galaxies typically have a lot of nearby stars. In fact, if you were to live on a planet near the center of the Milky Way, there would be so many stars you could read at night without using electricity.

4. Did Someone Leave the Oven On?

And not only would it be really bright, it would also be really toasty, thanks to radioactive heating! Those stars hanging around the black hole emit not just light but ghostly particles called neutrinos — speedy, tiny particles that weigh almost nothing and rarely interact with anything. While neutrinos coming from our Sun aren't enough to harm us, the volume that would be coming from the cluster of stars near a black hole would be enough to radioactively heat up whatever they slam into.

The planet would absorb neutrinos, which would, in turn, warm up the core of the planet eventually making it unbearably hot. It would be like living in a nuclear reactor. At least you’d be warm and could toss your winter coats?

5. You Are What You Eat?

If your planet got too close to a black hole, you’d likely face a gruesome fate. The forces from the black hole's gravity stretch matter, essentially turning it into a noodle. We call this spaghettification. (Beware the cosmic pasta-making machine?) Imagine yourself falling feet-first toward a black hole. Spaghettification happens because the gravity at your feet is sooooo much stronger than that at your head that you start to stretch out!

Credit: NASA

Light-year is the distance light travels in one year. Light zips through interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion miles (9.46 trillion kilometers) per hour.

How far can light travel in one minute? 11,160,000 miles. It takes 43.2 minutes for sunlight to reach Jupiter, about 484 million miles away. Light is fast, but the distances are vast. In an hour, light can travel 671 million miles.

Earth is about eight light minutes from the Sun. A trip at light-speed to the very edge of our solar system – the farthest reaches of the Oort Cloud, a collection of dormant comets way, way out there – would take about 1.87 years. Keep going to Proxima Centauri, our nearest neighboring star, and plan on arriving in 4.25 years at light speed.

When we talk about the enormity of the cosmos, it’s easy to toss out big numbers – but far more difficult to wrap our minds around just how large, how far, and how numerous celestial bodies really are.

To get a better sense, for instance, of the true distances to exoplanets – planets around other stars – we might start with the theater in which we find them, the Milky Way galaxy

Our galaxy is a gravitationally bound collection of stars, swirling in a spiral through space. Based on the deepest images obtained so far, it’s one of about 2 trillion galaxies in the observable universe. Groups of them are bound into clusters of galaxies, and these into superclusters; the superclusters are arranged in immense sheets stretching across the universe, interspersed with dark voids and lending the whole a kind of spiderweb structure. Our galaxy probably contains 100 to 400 billion stars, and is about 100,000 light-years across. That sounds huge, and it is, at least until we start comparing it to other galaxies. Our neighboring Andromeda galaxy, for example, is some 220,000 light-years wide. Another galaxy, IC 1101, spans as much as 4 million light-years.

Based on observations by NASA’s Kepler Space Telescope, we can confidently predict that every star you see in the sky probably hosts at least one planet. Realistically, we’re most likely talking about multi-planet systems rather than just single planets. In our galaxy of hundreds of billions of stars, this pushes the number of planets potentially into the trillions. Confirmed exoplanet detections (made by Kepler and other telescopes, both in space and on the ground) now come to more than 4,000 – and that’s from looking at only tiny slices of our galaxy. Many of these are small, rocky worlds that might be at the right temperature for liquid water to pool on their surfaces.

The nearest-known exoplanet is a small, probably rocky planet orbiting Proxima Centauri – the next star over from Earth. A little more than four light-years away, or 24 trillion miles. If an airline offered a flight there by jet, it would take 5 million years. Not much is known about this world; its close orbit and the periodic flaring of its star lower its chances of being habitable.

The TRAPPIST-1 system is seven planets, all roughly in Earth’s size range, orbiting a red dwarf star about 40 light-years away. They are very likely rocky, with four in the “habitable zone” – the orbital distance allowing potential liquid water on the surface. And computer modeling shows some have a good chance of being watery – or icy – worlds. In the next few years, we might learn whether they have atmospheres or oceans, or even signs of habitability.

One of the most distant exoplanets known to us in the Milky Way is Kepler-443b. Traveling at light speed, it would take 3,000 years to get there. Or 28 billion years, going 60 mph.

Credit: NASA

Life and Death of a Planetary System

How did we get here? How do stars and planets come into being? What happens during a star's life, and what fate will its planets meet when it dies? Come along on this interstellar journey through time and scientific detective work.

It all begins with an unimaginably cold cloud. This cloud contains the seeds of whole new worlds – stars and planets about to be born.

Molecules of hydrogen and helium gas, which normally zip around at high speeds, slow down and clump together because of gravity. Tiny grains of silicates, iron and carbon-rich material — together classified simply as "dust" — send some of the gas’s energy back out into space, making the cloud even colder. The dust grains spiral into the central knot of matter, like water running down a drain.

The newborn star is a feisty baby, shooting out violent jets of magnetically accelerated material as it gets nourishment from the gas and dust whirling around it. Like a blob of pizza dough flattening out as a chef spins it, this material condenses into a flat disk. That "dough" has a preferred direction inherited from the collapse of the cloud. That same spin will remain with the system for its entire life, unless another star system gets close enough to interact with it.

A very young disk around a star contains mostly gas with dust -- no bigger than grains of sand -- swirling around in it. The baby star is still throwing out extremely hot winds, dominated by positively charged particles called protons and neutral helium atoms. A lot of the material from the disk is still falling on the star. But small groups of lucky dust particles are crashing into one another, clumping into larger objects. Planets will form from less than 1 percent of the mass of the disk.

Based on just an image of baby planets in a protoplanetary disk, it is impossible to determine what the system will look like as it matures.

At approximately 100 million to 1 billion years old, planets tend to settle down in their orbits and stars don’t flare up as much. Our own solar system, about 4.5 billion years old, is the model for this idea of planetary "middle age." Mandell thinks of our planetary system as about 45 to 50 years old, when scaled down to a human lifetime.

When our Sun approaches its red giant phase some 6 billion years from now, it will run out of fuel in its core. As hydrogen fusion slows, the core once again begins to contract. As the core gets smaller, it heats up until can kick off another round of nuclear reactions, fusing helium into heavier elements such as carbon, nitrogen and oxygen. The hotter core also makes hydrogen fuse in the “shell” of material surrounding the core. Meanwhile, extra heat produced deep within in the star causes its outer layer of gas to puff up.

When the core of the former red giant has exhausted all of its fuel and shed all the gas it can, the remaining dense stellar cinder is called a white dwarf. The white dwarf is considered “dead” because atoms inside of it no longer fuse to give the star energy. But it still “shines” because it is so hot. Eventually, it will cool off and fade from view. Our Sun will reach this death about 8 billion years from now.

Credit: NASA