StarDate

An astronomer could probably spend an entire career studying a busy star system in the constellation Lyra. It’s a dynamic system in which two stars are changing as we watch.

Beta Lyrae is about a thousand light-years away. The system appears to consist of several stars. But the most interesting are two that are quite close together — they’re only a few million miles apart.

The stars probably were born about 25 million years ago. A study last year said that one of them was born about 10 times the mass of the Sun, with the other only seven times the Sun’s mass.

The heavier star evolved faster, so it reached the end of its life more quickly. It puffed up to become a giant. The gravity of the companion pulled on the closer side of the giant, sculpting it into the shape of a teardrop.

Gas began flowing from the narrow end of the teardrop toward the companion, and is still flowing today. The gas forms a swirling disk around the star. As gas funnels from the disk onto the star, it makes the star spin faster. That flattens the star a bit, so it looks more like a lozenge than a ball.

The donor star has dumped most of its mass onto the companion. So the once-heavier star is now only about a quarter the mass of its companion. And the process continues to play out, as one star gets bigger and the other gets smaller.

Look for Lyra high overhead as night falls, marked by its brightest star, Vega. Beta Lyrae is close by — a fainter star with an interesting story.

Script by Damond Benningfield

The most impressive tides on Earth vary by about 50 feet from high tide to low tide. But that’s barely a jiggle compared to the tides on Io, one of the moons of Jupiter. Its tides vary by the height of a 30-story building. That’s especially impressive when you consider that the rising and falling is in Io’s crust.

The tides have a serious impact on Io, which is about the same size as our own Moon. They create hundreds of volcanoes — more than on any other world in the solar system. And the volcanoes are giants. The biggest of them dwarf anything seen on Earth.

Io’s tides are caused by a non-stop tug of war between Jupiter and some of its other big moons. Their gravity pulls Io in different directions, stretching and squeezing its interior. That generates huge amounts of heat, which melts rock below the surface. Some of the magma pushes to the surface, forming volcanoes.

The biggest is Loki Patera, a pool of lava that covers 8,000 square miles — almost as big as New Jersey. It generates about 10 percent of Io’s heat. It last erupted in July. Its eruptions probably happen after the surface of the lava pool cools and hardens. The solid rock sinks and fresh lava rises to the surface — allowing Loki Patera to shine again.

And Jupiter is shining quite close to our moon tonight. The planet looks like a brilliant star. It’s to the lower right of the Moon as darkness falls. Through binoculars or a telescope, Io looks like a tiny star close to the giant planet.

Script by Damond Benningfield

The Moon has a couple of impressive companions this evening. Brilliant Jupiter is to the upper left of the Moon as night falls, with Antares closer to the lower left.

Jupiter is the largest planet in the solar system. But Antares is something even more impressive: a supergiant star. It’s hundreds of times the diameter of the Sun, and tens of thousands of times brighter.

At least it looks that way. We can’t be sure it’s actually still there. A supergiant ends its life with a titanic explosion — a supernova. The blast rips the star to bits, leaving only its tiny, dead core. And astronomers know that Antares is close to the end of its life. In fact, it’s entirely possible that Antares has already exploded but we just don’t know it yet.

That’s because light travels at a limited speed. It’s a really fast speed — 670 million miles per hour. Nothing in the universe can travel faster. Even so, Antares is so far away that its light takes more than five centuries to reach us. So perhaps Antares has already exploded, and the light of the blast is still rushing our way.

Thanks to that finite speed of light, even the Sun could vanish without our noticing it right away. It would take more than eight minutes from the time the Sun vanished until its final light rays reached Earth.

Fortunately for us, the Sun isn’t going anywhere. It’ll remain in the prime of life for billions of years more — shining down on Earth from eight light-minutes away.

Script by Damond Benningfield

To most of us, the titles of most research papers are dense and dull. But a paper published in July would draw just about anyone’s interest: Death by Dark Matter. In the paper, researchers looked to see if people were being killed by a possible form of dark matter. The conclusion: We’re safe.

Dark matter is far more abundant than normal matter — the kind that makes up stars, planets, and people. We can’t see dark matter because it doesn’t interact with normal matter. But we know it’s there because it exerts a gravitational pull on what we can see.

Scientists have proposed many possible explanations for dark matter. They range from tiny subatomic particles to black holes left over from the Big Bang. The leading idea says it consists of fairly heavy particles. But efforts to find those particles have turned up empty.

Another idea says the dark matter could consist of tiny clumps of normal particles. But they’d be arranged and held together in odd ways, so they’d be extremely dense and heavy — up to a hundred pounds.

A couple of researchers calculated that if such a clump zipped through a human body, it would act like a tiny but powerful bullet. It would bore a narrow hole, and heat the tissue around it to millions of degrees.

The researchers analyzed 10 years of medical records from North America and Europe. And they found no likely cases of death by dark matter. That reduces the chance that such a heavy form of dark matter exists — luckily for us.

Script by Damond Benningfield

ET may be phoning home, but he’s not calling anyone else — not that we’ve heard, anyway. So far, the most extensive search for extraterrestrial intelligence to date has turned up empty. But the project isn’t giving up. In fact, it’s expanding the search by adding new telescopes.

Breakthrough Listen has been operating for about four years. It uses giant radio telescopes in the U.S. and Australia. They monitor billions of frequencies for signals from other civilizations. The project has kept an “ear” on more than 1300 stars that are within about 160 light-years of Earth. It’s also looked toward the center of the Milky Way Galaxy, and at several other galaxies.

But a couple of months ago, project scientists reported they haven’t heard a peep. All the interesting signals have been made either by human technology, or they’re produced naturally, by stars and other objects.

Yet the search is just getting started. It recently added a large array of radio telescopes in South Africa. The array should be able to “hear” more-distant signals. That will allow the project to monitor a million individual stars.

In addition to radio telescopes, Breakthrough Listen has used an optical telescope to look for laser beams. Such beams might be used for interstellar communication, or to push sail-powered spacecraft. And the project has added an array of four telescopes in Arizona to that part of the search — extending its efforts to find ET.

Script by Damond Benningfield

Summer ended less than a week ago, but you can already get a preview of the evening skies of winter in the hours before sunrise.

Winter’s evening-sky highlights include the constellations Orion and Gemini, along with Sirius, the brightest star in the night sky. All of them are in view by about 4 a.m., and are high in the sky at first light.

Orion is in the south and southeast as dawn breaks. It’s best identified by the hunter’s “belt” of three fairly bright stars. The brightest stars in the constellation flank the belt: orange Betelgeuse to the upper left, and blue-white Rigel to the lower right.

Orion’s Belt points the way to Sirius. Just follow its line toward the lower left and you’ll come across the brilliant star. It’s in Canis Major, the big dog, so it’s also known as the Dog Star. Because Sirius is so bright, it twinkles more than most other stars. It switches from white to red to blue in the blink of an eye.

Gemini is well to the left of Orion. It’s noted for the bright stars Castor and Pollux, which represent the heads of the celestial twins. Pollux is the brighter of the two, and has a definite orange hue. Castor is above it.

As Earth moves along its orbit around the Sun, all these beautiful sights rise a few minutes earlier each night. So in a few months, they’ll highlight the evening sky — putting on a strong showing throughout the long, cold nights of winter.

Tomorrow: continuing the search for aliens.

Script by Damond Benningfield

Venus is trying to climb into view in the evening sky. The planet is very low in the west at sunset, and it sets well before twilight fades. It’s the brightest object in the sky other than the Sun and Moon, though, so it’s worth a try.

Venus is the second-closest planet to the Sun, so it’s inside Earth’s orbit. As a result, it always stays fairly close to the Sun in our sky. At best, it’s visible for a while after sunset or before sunrise.

Venus passed behind the Sun last month. Now, it’s pulling away from the Sun. Because of the relative motions of Venus and Earth, though, it doesn't gain much ground from day to day. So it’s still only a few degrees away from the Sun, which keeps it immersed in the Sun’s glare.

And things are made worse by the time of year. The path Venus follows across the sky is tilted low at sunset. So instead of popping straight up into the sky, Venus glides at a low angle across the horizon. That keeps it low in the sky, and hard to see.

It’s especially hard to see from northern latitudes. The view is better from southern locations — Houston or Miami, for example — because Venus rises at a slightly better angle.

Tomorrow night is a good time to look for Venus. It’ll appear to the lower right of the Moon shortly after sunset. It’ll look like a bright star just above the horizon. Venus will climb into better view over the coming weeks. By late October, it’ll be visible from the whole country — as the bold “evening star.”

Script by Damond Benningfield

The galaxy is full of binary star systems — two stars bound together by gravity. The list includes pairs of massive stars. And when those stars die, they can leave behind heavy but invisible corpses: black holes.

Astronomers haven’t seen a single black-hole binary. That’s not surprising, since black holes produce no energy. We know such binaries exist, though, because astronomers can hear them. They’ve detected the mergers of binary black holes as they spiral together.

A black-hole binary can form when the cores of two paired supergiant stars collapse. It also can form when two non-paired black holes stage a gravitational encounter with a third star. The third one gets kicked away, while the black holes become bound to each other.

Scientists have discovered the mergers of about a dozen black-hole binaries. They “listened” for gravitational waves — ripples in space-time created by the merging black holes.

The first merger was discovered four years ago. As the black holes got closer, they orbited faster, causing them to emit more waves.

Astronomers found that both black holes were at least 30 times the mass of the Sun. And in the last 20 milliseconds before they merged, they produced more energy — in the form of gravitational waves — than all the energy produced by all the visible stars in the universe. The waves carried away the equivalent of three times the mass of the Sun — waves that confirmed the existence of binary black holes.

Script by Damond Benningfield

A monster black hole sits at the center of the Milky Way Galaxy. And it’s probably surrounded by many thousands of smaller black holes. But that’s just the beginning. There could be hundreds of millions of black holes spread throughout the galaxy.

A black hole is so heavy and dense that nothing can escape its gravitational pull — not even light. That means we can’t see a black hole on its own. But there are lots of indirect ways to see them, including their effects on the stars and gas around them. Astronomers have even taken a picture of one — a dark silhouette against a glowing background.

So far, a few dozen black holes have been confirmed in the Milky Way. The biggest is the one in the galaxy’s heart. It’s about four million times the mass of the Sun.

But most black holes are much smaller — from a few to a few dozen times the Sun’s mass. Such black holes form when massive stars collapse. Most of these black holes travel through the galaxy alone, so there’s not much way to see them.

The ones we know about have “normal” companion stars. Astronomers detect a black hole’s gravitational influence on such a companion, or they see it “stealing” some of the companion’s gas.

From these discoveries, and estimates of how many massive stars have lived and died in the Milky Way, astronomers deduce how many black holes the galaxy should host. The numbers vary. But most are in the range of a few hundred million — black holes galore in our home galaxy.

Script by Damond Benningfield

Most stars end their lives with a blaze of color — an expanding bubble of gas and dust known as a planetary nebula.

A comet-hunting astronomer, Charles Messier, discovered the first planetary nebula more than 250 years ago. It’s known as M27 — the 27th entry in Messier’s catalog of comet-like objects.

A planetary nebula forms when a star exhausts the nuclear fuel in its core. The core collapses and eventually forms a dense, hot ember called a white dwarf. Radiation from the sizzling-hot core pushes away the star’s outer layers, creating an ever-expanding bubble. The radiation causes the gas to glow like a fluorescent bulb.

As seen from afar, these clouds can look like rings, cat’s eyes, pearl necklaces, or glowing atoms. And M27 resembles a hand weight like you’d use at the gym — hence another of its names: the Dumbbell Nebula.

The Dumbbell has been expanding for thousands of years. And it will remain visible for thousands of years more. Eventually, though, it’ll become so large and thinly spread that it will fade from sight. But its story won’t be done. Millions or billions of years from now, some of the Dumbbell’s gas and dust may be incorporated into new stars and planets — an act of rebirth from the remains of a dead star.

The Dumbbell is in Vulpecula, the fox. The constellation is high overhead as night falls. The nebula is about halfway between Deneb and Altair, the bright stars that mark one side of the Summer Triangle.

Script by Damond Benningfield