StarDate

A giant planet that’s orbiting a dead star is tough. It survived the star’s demise — a process that sent big blobs of hot gas flying out into space. And it’ll probably survive being eroded away by the star’s hot corpse.

The planet orbits a white dwarf — the remnant of a once “normal” star. As the star died, it expelled its outer layers into space, leaving only its hot core. The core is more than half as massive as the Sun, but only about one percent as wide — about the size of Earth.

Astronomers in Europe discovered a disk of gas and dust around the white dwarf. From the size and composition of the disk, they concluded that it’s being fed by a planet. It’s the first planet known to orbit a white dwarf.

The planet is several times the size of the white dwarf. That makes it about as big as Uranus or Neptune, two of the giants of our own solar system. But radiation from the white dwarf is blasting away the planet’s outer layers — at 3,000 tons per second. Much of the debris spirals toward the star, forming the disk.

The researchers say the planet should survive the stellar blowtorch, though. It’ll lose only a small fraction of its mass. It will continue to orbit the dead star as it slowly cools and fades into the long cosmic night.

The system is about 2,000 light-years away. It’s in Cancer, the crab, which is high overhead as night falls. It’s far too faint, though, to see without a telescope.

We’ll talk about a hot moon tomorrow.

Script by Damond Benningfield

The planets Mars and Saturn don’t have a lot in common. Mars is small, dense, and rocky. Saturn probably has a rocky core, but most of it is made up of gas. So while Saturn is many times larger than Mars, it’s the “fluffiest” planet in the solar system.

One possible similarity, though, is rings. Saturn is encircled by wide, beautiful rings. Mars doesn’t have any rings today, but it could have had them in the distant past — and might again millions of years in the future.

Saturn’s rings probably formed when a small moon was pulverized. The moon might have passed too close to Saturn and was pulled apart by Saturn’s gravity. Or it might have been shattered by a collision with another body.

Mars could have been smacked by a smaller object billions of years ago, creating its own rings. Some of that debris might have coalesced to form the planet’s moons, Phobos and Deimos.

Phobos is only 3700 miles above the Martian surface. And it’s sliding closer — by about six feet per century. In 50 million years or so, it’ll either crash into Mars, or be pulled apart by the planet’s gravity — creating a new ring.

Mars and Saturn are forming a tight pair in the early morning sky. They’re low in the southeast at first light, to the lower left of brilliant Jupiter. Tomorrow, Mars will stand a little below Saturn. After that, Mars will slide away from Saturn. In a few days, that’ll break up the pairing of these quite-different siblings.

Script by Damond Benningfield

With every breath, you’re inhaling the “ash” from a nuclear furnace — nitrogen and oxygen created by a star. Many stars are making more of these elements today, and will someday expel them into space — perhaps to fill the skies of future planets.

One star that’s made a lot of nitrogen is Arneb, the leading light of the constellation Lepus, the hare. It’s in the southwest as night falls, below brilliant Orion.

Arneb is roughly 14 times the mass of the Sun. Such heavy stars “burn” through the hydrogen fuel in their cores in a hurry. They smash together the hydrogen to make helium. But they do it in a different way from stars like the Sun.

The Sun makes helium directly by fusing the nuclei of hydrogen atoms — bare protons. But stars like Arneb use a catalyst: carbon, which is present in small amounts when the star is born.

In a series of steps, the carbon fuses with hydrogen to make nitrogen, followed by a heavier form of carbon. This carbon then splits apart. That yields helium plus the type of carbon that started the whole thing. So hydrogen is converted to helium, while the carbon is still around to continue the process.

In Arneb, some of the nitrogen created in this sequence has survived. It’s mixed with the star’s outer layers. Arneb eventually will blast the nitrogen and other elements created inside the star out into space. That will seed the galaxy with the ingredients for new stars, planets — and planetary atmospheres.

Script by Damond Benningfield

The clouds of Venus are especially bright. They reflect about two-thirds of the sunlight that strikes them. That makes Venus a brilliant target in our night sky.

Yet there are dark sheets inside the clouds. They absorb ultraviolet energy from the Sun. They could be caused by volcanoes. But it’s also possible they could be big “mats” of bacteria — perhaps the survivors of a once-thriving planet.

Today, the surface of Venus is decidedly un-friendly. The temperature is 865 degrees, the “air” is made of carbon dioxide, and the pressure is equal to a depth of two-thirds of a mile in Earth’s oceans. No Earthly organisms could survive those harsh conditions.

Yet some Earthly bacteria could survive about 30 to 40 miles above Venus’s surface. Temperatures and pressures are similar to those at Earth’s surface. And the clouds are made of sulfuric acid — a source of chemical energy to help sustain the bacteria.

It’s possible that Venus was comfortable for billions of years. That could have been enough time for life to evolve — then move to the clouds when conditions got worse,

No Venus-orbiting spacecraft has had the ability to measure the composition of the dark regions in the clouds. But future missions might target them — perhaps telling us if anything is living on our sister world.

And Venus teams with the crescent Moon to put on a great show this evening. They’re well up in the sky at nightfall, and don’t set until shortly before midnight.

Script by Damond Benningfield

It’s not unusual for a husband to take a picture of his wife displaying her wedding ring. Until Wilhelm Roentgen came along, though, none had taken a picture of not just the ring, but of the bones beneath it. Roentgen had just discovered X-rays — a form of light that can pass right through many substances, including human flesh. The shot of his wife’s hand — including her ring — was the first X-ray image.

Roentgen was born 175 years ago today, in Germany. His family moved to the Netherlands when he was three. He developed an interest in the outdoors, and in building mechanical devices. But he also wanted to learn how the universe works, so he earned a PhD in physics in Switzerland.

In 1895, Roentgen was studying a form of energy that’s produced when an electric charge is passed through a vacuum tube. He put his test rig inside a black box, which was in a dark room. When he set if off, though, it caused a light-sensitive screen a few feet away to glow.

Roentgen decided that his equipment was producing a new form of rays. He called them X-rays, although others called them Roentgen rays.

Scientists found a way to put those rays to work. Eventually, that included astronomers, who study X-rays produced by objects in the sky. The list includes the remnants of exploded stars, disks of hot gas around black holes, and clouds of gas around clusters of galaxies. The observations help astronomers “diagnose” how these objects work — thanks to X-rays.

Script by Damond Benningfield

Betelgeuse lost some of its luster in recent months. By early this year, the supergiant star was fainter than it had been in a long time. That dropped it not only from the top 10 brightest stars in the night sky, but from the top 20. And astronomers are trying to figure out what that means.

Betelgeuse forms the shoulder of Orion the hunter. It’s high in the southwest as night falls, and shines bright orange.

The star is one of the most impressive in our part of the galaxy. It’s a dozen or more times the mass of the Sun, and hundreds of times the Sun’s diameter. If it took the Sun’s place, in fact, it would engulf the four inner planets, including Earth. And it might reach all the way to the fifth planet, Jupiter.

That’s the star’s average size. Betelgeuse puffs in and out like a beating heart, getting bigger and smaller with each beat — and brighter and fainter.

Its recent fade, though, made it fainter than has ever been recorded with modern instruments. That led to speculation that Betelgeuse was about to explode as a supernova. And someday, it will — in the next hundred thousand years or so.

Instead, Betelgeuse might have appeared so faint because it has several overlapping “beats,” and two of them reached their low points at the same time. Or perhaps the star expelled a lot of dust, creating a dense “fog” around itself.

Whatever the reason, astronomers say this impressive star is likely to hang around for a long time to come.

Script by Damond Benningfield

NGC 4449 is small but busy. The dwarf galaxy looks like it’s recently merged with a couple of other galaxies. It’s forming stars at a rapid pace — star for star, much faster than in our home galaxy, the Milky Way. And it’s blowing a “wind” of hydrogen and heavier elements into the space around it.

But the wind isn’t nearly as thick or as extensive as theory predicts. So the ideas about how such galaxies evolve, and how they interact with the rest of the universe, may need work.

NGC 4449 was one of a dozen dwarf galaxies targeted in a recent study, led by Kristen McQuinn of Rutgers and the University of Texas. Earlier work had shown that the galaxies were giving birth to many stars. The new study looked at how much gas the galaxies were blowing out into space.

Theory said they should be expelling a lot of it — the result of stellar explosions. It also predicted that the winds would contain a lot of material heavier than hydrogen and helium, the lightest elements.

But while most of the galaxies are pumping out some gas, it isn’t nearly as much as expected. Much of what they are expelling could fall back in. And the chemistry isn’t right, either.

So theorists have some work to do to explain the behavior of some of the smallest galaxies.

NGC 4449 is in the northeast as night falls, not far from the Big Dipper. The galaxy is about 12 million light-years away. And it’s so faint that you need a telescope to see it.

Script by Damond Benningfield
 

TODAY'S PROGRAM WAS MADE POSSIBLE BY THE NATIONAL SCIENCE FOUNDATION

Our home galaxy, the Milky Way, is the hub of a galactic empire. It’s not the kind with death stars and Jedi knights, though. Instead, it’s an empire of smaller galaxies. About 50 of these “dwarf” galaxies orbit the Milky Way, held in place by its powerful gravity.

As those numbers suggest, dwarf galaxies are the most common type of galaxy in the universe. They outnumber giants like the Milky Way by a wide margin. But it takes a whole mess of them to add up to much. In fact, the Milky Way is more massive than all the dwarf galaxies it commands combined.

Some of these cosmic “puffballs” may have been pulled out of larger galaxies by encounters between big galaxies. But most of them probably formed in the early universe — the very first collections of stars.

The galaxies were packed together tightly, so many of them began to merge. That’s probably how most of the big galaxies took shape — through mergers between the little guys.

And that process continues today. We see many large galaxies gobbling up the dwarfs. That includes the Milky Way. There’s evidence that it’s consumed quite a few smaller galaxies during its long lifetime. And astronomers have discovered one galaxy that’s being consumed by the Milky Way now, and others that were pulled in fairly recently. All of them will lose their galactic identity — their stars pulled away from them by the mighty Milky Way.

We’ll have more about dwarf galaxies tomorrow.

Script by Damond Benningfield

The planet Venus is at its towering best right now. The “evening star” is high in the west at sunset — just about as high up as it ever gets. And it doesn’t set until 11 or 12, providing plenty of time to watch it.

Venus is the second planet from the Sun, while Earth is the third planet. So as seen from Earth, Venus never strays very far from the Sun. It’s visible for up to a few hours before sunrise or after sunset, but no more — it can’t remain in the sky all night, as some of the other planets do.

And for the next few days, it’s at its greatest extension from the Sun — about 46 degrees. Its path across the sky is tilted a bit, though, so it doesn’t stand quite that high above the horizon as the Sun sets. Still, this is just about as high in the evening sky as you’ll ever see it.

Because of the giant gap between Sun and Venus, this is a good time to look for the planet during daylight. It’s bright enough to see without any help — no binoculars or telescope are needed. It’s tough to pick out against the blue sky, though. But once you find it, it’s pretty easy to go back to.

A couple of hours before sunset, for example, Venus is high in the southwest. It’s to the upper left of the Sun, by about four and a half times the width of your fist at arm’s length.

If you can’t find it, though, no worries. Venus will be plenty bright once the Sun sets, and will remain in view until almost midnight — a long performance for the “evening star.”

Script by Damond Benningfield

Several bright stars are identified as “hearts.” Regulus, for example, is the heart of the celestial lion, while Antares is the heart of the scorpion. One of the few whose name actually means “the heart” is in good view on spring evenings. Cor Caroli is the brightest star of Canes Venatici, the hunting dogs. It’s in the east as night falls, to the right of the tip of the Big Dipper’s handle.

But the star’s name doesn’t refer to its constellation. Instead, Cor Caroli means “Heart of Charles.” It was named in the 1600s, and it refers to either England’s King Charles I, or his son, Charles II.

Perhaps fittingly, Cor Caroli consists of two stars. One of them is a good bit bigger and heavier than the Sun, and a hundred times brighter. The other also outdoes the Sun, although it’s not as impressive as its sibling.

The brighter star is the prototype of an entire class of stars. They get brighter and fainter over a period of a few days. The change probably is caused by starspots — giant magnetic storms on the star’s surface. They’re darker than the surrounding gas. So as they rotate into view, the star’s overall brightness goes down a bit.

The storms are driven by the star’s high-speed rotation. Despite its great size, it spins once every five-and-a-half days, versus about once a month for the Sun. That stirs up the star’s outer layers of gas, creating a powerful magnetic field — and giving Charles a “stormy” heart.

Script by Damond Benningfield