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
-------- Â
2:14
Eta Carinae
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
-------- Â
2:14
Sandy Skies
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
-------- Â
2:14
Groundhog Day
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
-------- Â
2:14
Moon and Venus
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
USA