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Magnetic Zombie Feb 05, 2025

An odd “zombie” star has grabbed its companion in a magnetic embrace. It keeps the two stars synchronized, and it pulls gas from the companion.

The system is A-M Herculis. It’s almost 300 light-years away, in the constellation Hercules.

The main star in the system is a white dwarf — the corpse of a once-normal star. It’s about two-thirds as massive as the Sun, but only about as big as Earth. That means it’s extremely dense, so its gravity is strong.

The star’s magnetic field is millions of times stronger than the Sun’s. And that’s bad for the companion – a cool, faint ember known as a red dwarf. The stars are so close that they orbit each other every three hours. At that range, the magnetic field of the white dwarf exerts a powerful pull. It’s made the two stars rotate in such a way that the same hemisphere of each star always faces the other – just as the same hemisphere of the Moon always faces Earth.

The field also pulls gas from the companion. In most systems like this, the infalling gas forms a wide, spinning disk. But in the case of A-M Herculis, it plunges directly onto the white dwarf, guided by the magnetic field. The streamer varies – thicker at some times, thinner at others. But it piles onto the poles of the white dwarf, making the star hotter and brighter – renewed vigor for a stellar zombie.

Hercules is high in the sky at dawn. But A-M Herc is much too faint to see without a telescope.

Script by Damond Benningfield

Eta Carinae Feb 04, 2025

One of the most amazing star systems in the galaxy is only 7500 light-years away. In the 1800s, it shined brighter than only one other star in the entire night sky. And combined, its two stars are at least five million times brighter than the Sun. Yet no one has ever seen either star directly – they’re encased in a cocoon of their own making.

Eta Carinae appears to consist of two supergiants. One of them may be a hundred times the mass of the Sun – one of the heaviest stars yet discovered. The other is perhaps 30 times the Sun’s mass or more.

Almost two centuries ago, the system began to flare up. Astronomers still aren’t quite sure why. Perhaps one of the stars engulfed a third member of the system. Or perhaps the two stars passed especially close together, and their gravity ripped out big torrents of hot gas.

Whatever the reason, over a couple of decades Eta Carinae grew especially bright. Then it faded from view. That’s because the two stars had expelled a huge amount of gas – enough to make 20 stars like the Sun. The material cooled, wrapping the stars in a dense nebula. It’s shaped like an hourglass, with a sheet extending from its waist like a ballerina’s tutu

The stars are only about three million years old. But the heavier one could expire at any time. It could explode as an especially bright supernova. Or it might collapse to form a black hole – a dark fate for a brilliant star.

Script by Damond Benningfield

Sandy Skies Feb 03, 2025

Clouds made of sand may scud across the skies of a pair of brown dwarfs – “failed stars” that are among the Sun’s closest neighbors. The clouds move in a hurry – they can change the appearance of the brown dwarfs over just a few hours.

The system is known as Luhman 16. It’s just six and a half light-years away – about two light-years farther than the closest star system, Alpha Centauri. But it wasn’t discovered until about a decade ago because it’s extremely faint. It’s in the constellation Vela, which just peeks into view late tonight for skywatchers in the far-southern United States.

Luhman 16 is a binary, so the two brown dwarfs are locked in orbit around each other. Both of them are about 30 to 35 times the mass of Jupiter, the largest planet in the solar system. That makes them too massive to be planets, but not massive enough to shine as true stars.

The surfaces of both objects are hot, but not nearly as hot as the Sun. That allows molecules to condense and form clouds.

Researchers examined the system with instruments aboard Webb Space Telescope. The instruments are sensitive to different wavelengths of light, so they reveal different details. They found clouds made of silicate – grains of sand. They also found water, carbon monoxide, and methane. The compounds were found at different depths in the atmosphere. So the observations provided a 3-D look at the busy skies of these faint neighbors.

Script by Damond Benningfield

Groundhog Day Feb 02, 2025

If you just can’t wait for spring, you might want to use one of the calendar markers of long-ago Europe and the British Isles. In their traditions, early February marked the end of winter and the start of spring. The days were getting longer and warmer, with the promise of even more sunlight to come.

Early February falls roughly half way between the winter solstice and the spring equinox. Such midpoints are known as cross-quarter days. That means they cross between the quarter days – the solstices and equinoxes.

Early Christians celebrated February 2nd as Candlemas. It was the 40th day of Christmas. People brought their candles to church to have them blessed for the whole year.

In Ireland and Scotland, the February celebration came on the 1st. It was known as Imbolc. The name may indicate the start of lambing season, although it could have other meanings as well.

One of the traditions of Imbolc concerned the weather. If the day was sunny and cold, it meant winter would maintain its icy grip until the equinox, about six weeks away. But if the day was warm and cloudy, then winter was just about over. Some people relied on badgers or other animals to come out of their dens to check out the conditions.

That tradition was carried to the United States by immigrants. And it’s still with us today as Groundhog Day – a modern celebration of a cross-quarter day – one that marked the beginning of spring.

Script by Damond Benningfield

Moon and Venus Feb 01, 2025

Two Greek goddesses huddle close together in the sky this evening: Selene and Aphrodite – the Moon and Venus. They’re in good view well before night falls, shining through the twilight.

Aphrodite was the goddess of love and beauty. She was identified with the brilliant morning and evening star. We know them today by her Roman name, Venus. Selene was one of several Moon goddesses, but the only one considered to be the human form of the Moon itself.

Selene’s name has been applied to a lot more than just the Moon. Among other things, it’s the name of a mineral – selenite – and an element – selenium.

Selenite is a crystal form of the mineral gypsum. It’s translucent, so it was sometimes used as window panes. There are several possible explanations for the name. One says it might have been bestowed because the light that passed through the windows looked milky white – like the light of a bright Moon.

Selenite doesn’t contain any selenium, though. The only thing the mineral and the element have in common is the name. Selenium was discovered in the early 1800s. It’s rare – usually found mixed in with the ores of various metals. Its appearance and properties were similar to those of another recently discovered element – “tellurium” – a word that means “Earth.” So it made sense to name the new one for our satellite world – the Moon.

Tomorrow: a different seasonal dividing line.

Script by Damond Benningfield

Moon and Saturn Jan 31, 2025

All of the Sun’s major planets are a bit flattened – they’re bigger through the equator than through the poles. For Mercury and Venus, the difference is only a few miles. For Earth, it’s about 20 miles. But for Saturn, it’s more than seven thousand miles. Such a big difference is obvious even to the eye alone: The giant planet looks like a squashed beachball.

The planets are flattened because they’re spinning. The rotation pushes material outward. Solid bodies like Earth are stiff, and they don’t rotate all that fast, so they’re not deformed by much. But Saturn and the other giant worlds don’t have solid surfaces. That makes it easier to push stuff away from the center as the planet spins.

Saturn is flatter than the other giants. That’s mainly because it’s less dense than the others. That means its surface gravity isn’t as strong, so it doesn’t grip material at the surface as tightly.

And Saturn spins in a hurry – roughly once every 10 and a half hours, although the exact timing is still uncertain. That means the planet’s equator rotates at more than 21,000 miles per hour – 20 times faster than Earth’s equator. That slings material outward with great force – making Saturn the most “smushed” planet in the solar system.

Look for Saturn near the crescent Moon early this evening. The planet looks like a bright star above the Moon as twilight fades. They set a couple of hours after sunset.

Script by Damond Benningfield

Messier 37 Jan 30, 2025

The constellation Auriga is high in the eastern sky as night falls. It’s usually drawn as a pentagon. The brilliant star Capella is at the top left corner, with fainter Elnath – a star that’s shared with Taurus – at the lower right.

A trail of three prominent star clusters winds through the pentagon – Messier 36, 37, and 38. M36 and 38 are inside the pentagon. M37 is just below it. All three are easy targets for binoculars.

M37 is about 4500 light-years away. And it’s the largest of the trio of clusters. It spans a few dozen light-years. Astronomers have cataloged more than 500 member stars, but the total population could be much higher. The cluster includes more than 50 dead stars known as white dwarfs. The details of such stars help reveal the cluster’s age – roughly 400 million to 550 million years.

And that’s a long time for a star cluster to hang together. M37 has orbited the center of the Milky Way Galaxy at least twice. As it orbits, the gravitational fingers of other stars and gas clouds pull away some of the stars on the fringes of the cluster.

So far, Messier 37 appears to be maintaining a firm grip on most of its stars. But that won’t last forever. More stars will be pulled away on each trip through the galaxy – whittling down this tight family of stars.

Script by Damond Benningfield

Old Ears Jan 29, 2025

For decades, the DSS-28 radio antenna in the California desert listened to the faint whisper of spacecraft exploring the solar system. It’s still listening for artificial radio signals today – the faint whisper of other civilizations. It’s controlled by students around the country and around the world.

DSS-28 is a radio dish more than a hundred feet in diameter. It was built for the Army, then transferred to NASA. It was decommissioned in the 1980s. But 40 years ago, a kindergarten teacher in California found a new use for it – as an educational tool for teachers and students.

It’s the centerpiece of the Goldstone Apple Valley Radio Telescope project. Teachers train to use the telescope, and pass that knowledge on to their students. The students then work with scientists to observe stars, planets, and other objects.

Current projects include studies of the radio waves from Jupiter; the busy regions around supermassive black holes in other galaxies; and the connection between sunspots and the Sun’s hot outer atmosphere.

Another project is SETI – the search for extraterrestrial intelligence. Students have been using the telescope to scan the galactic plane – the region that outlines the disk of the Milky Way Galaxy. The first phase found no signals from other civilizations. But the telescope will scan more slices of the galaxy in the coming years – still listening for radio signals from beyond Earth.

Script by Damond Benningfield

NGC 2273 Jan 28, 2025

The Big Dipper is low in the northeast at nightfall, ready to climb high across the north during the night. The prominent constellations Gemini and Orion are far to its upper right. But the space between them looks dark and empty. There’s just not much to see – especially from light-polluted cities. In fact, the main feature in the gap is named for its faintness. The constellation Lynx was given its name because you need the sharp eyes of a lynx to see any of its stars.

A telescope reveals some impressive sights, though. That includes the galaxy NGC 2273 – a galaxy within a galaxy. It’s about as big and as massive as our own home galaxy, the Milky Way. It has a small, tight spiral in its middle, with a wider spiral around it.

A supermassive black hole inhabits the galaxy’s heart. The black hole produces enormous amounts of radio waves. That tells us the black hole is feeding voraciously. As gas and dust spiral toward the black hole they form a wide, hot disk around it. Some of the material in the disk is funneled into “jets” that shoot into space at almost the speed of light. The jets produce radio waves.

The jets and other evidence show that the black hole is about seven and a half million times as massive as the Sun. That’s about twice as heavy as the black hole at the center of the Milky Way – an impressive zone of darkness in a dark region of the night sky.

Script by Damond Benningfield

Black Hole Snack Jan 27, 2025

Astronomers will keep a close eye on a distant galaxy later this year. They’ll be looking to see if a giant black hole is once again feasting on a star.

The system is known as AT2018fyk. It was discovered in 2018, when a galaxy 860 million light-years away flared brightly. The flare-up happened when a star flew too close to a black hole about 50 million times the mass of the Sun. The black hole appeared to rip the star to bits and gobble up the debris.

A couple of years later, though, the system flared again. That means the star survived the encounter – or at least some of it did. When the star once again came close, the black hole took another bite.

Last year, researchers concluded that the star originally was a member of a binary – two stars locked in orbit around each other. But the black hole split the binary apart. One of the stars was fired away like a cosmic bullet. The other entered a lopsided orbit around the black hole. It orbits once every three and a half years.

When the star gets close to the black hole, it loses some of its gas. The gas spreads out along the star’s orbit. Every year and a half, the gas begins to pour into the black hole. It heats up and glows brightly.

If that model is right, the system should brighten again this summer. So astronomers will be watching – to see if a black hole takes another bite of a star.

We’ll talk about another black hole tomorrow.

Script by Damond Benningfield

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