StarDate

The story of a black hole in Cygnus, the swan, is like the tale of an angler – there’s the star it caught, and the one that got away.

V404 Cygni is about 7800 light-years away. It appears fairly close to the star that marks the intersection of the swan’s body and wings, which is high in the sky at dawn.

The system was first noticed in 1938, when it flared up – a performance it’s repeated several times.

Later, it was discovered that V404 Cygni is a tight binary: a black hole about nine times the mass of the Sun, plus a “normal” star a little less massive than the Sun.

The black hole is pulling gas from the companion. The gas forms a disk around the black hole. Every couple of decades, so much gas piles up that it sets off an explosion. That makes the system shine thousands of times brighter.

Recently, astronomers found that what looked like a background star probably is bound to the other two. It’s more than 300 billion miles from them. It’s bigger and heavier than the Sun, and is puffing up to become a giant.

This third star is about four billion years old – suggesting that the black hole is also that old. The black hole is the corpse of a massive star. Most such stars explode, hurling away any companions. This star must have collapsed completely, without exploding. Since then, it’s consumed at least half of its close companion – but the distant one got away.

Script by Damond Benningfield

The most amazing object visible through a small telescope doesn’t look all that remarkable. In fact, it looks like a faint star. Yet that point of light packs the power of 10 trillion Suns – the power of a quasar.

3C 273 is the first quasar ever discovered. When astronomers first saw it, they thought it was just another star. It looks like a star, and its main ingredient is like a star’s as well. But when they measured its distance, they were astonished: 3C 273 was two and a half billion light-years away. That meant it couldn’t be a star at all. Instead, they classified it as a quasi-stellar object – a quasar.

Astronomers eventually figured out that it’s powered by a black hole at the heart of a giant galaxy. The black hole is about 900 million times the mass of the Sun. Its enormous gravity pulls in huge amounts of gas and dust, and maybe some stars. That material forms a spinning disk around the black hole. The disk is heated to millions of degrees, so it shines brilliantly – bright enough to see from two and a half billion light-years away.

3C 273 is in Virgo. The constellation’s brightest star, Spica, is low in the southeast at nightfall. The quasar stands high above it, about a third of the way up the sky. Despite its great power, it’s too faint to see with the eye alone. But a telescope reveals this deceptive wonder – a monster masquerading as a star.

Script by Damond Benningfield

The mild nights of spring are good times for skywatching. Only one thing is missing: a great meteor shower. The best showers are clustered in fall and winter, with the Perseids of August sometimes joining the list.

Although the season doesn’t offer a great shower, a pretty good one should reach its peak tomorrow night: the Lyrids. Under a dark sky, you might see up to a couple of dozen meteors per hour between midnight and dawn. The number of meteors increases closer to dawn, as your part of Earth turns more directly into the meteor stream. Unfortunately, by then the waning Moon will be in the sky, so its light will compete with the fainter meteors.

One good thing about meteors, though, is that you don’t have to wait for a shower to see them.

A shower occurs when Earth passes through a stream of small bits of dust and rock shed by a comet or asteroid. There are many showers through the year, but only a few are noticeable.

But bits of rocky debris are scattered throughout the solar system. So on any dark night, you can see several meteors zipping across the sky. And these “random” meteors can come from any direction and blaze across any part of the sky.

So if you have a chance, look for the Lyrid meteor shower in the wee hours of Tuesday morning. If not, then take advantage of just about any clear, dark night to look for meteors flashing across the heavens.

Tomorrow: a steady light far across the galaxy.

Script by Damond Benningfield

The Sun is four and a half billion years old – a third of the age of the universe. Compared to the stars in globular clusters, though, it’s a youngster. Those stars were born when the universe was young.

An example is Messier 3 – a family of about half a million stars. The cluster is about 11.4 billion years old. That means its stars were born just a couple of billion years after the Big Bang.

All of the cluster’s remaining original stars are fainter and less massive than the Sun. Anything heavier than the Sun has exhausted its nuclear fuel, leaving only a corpse – a small, dense, faint remnant. And astronomers have seen quite a few of these remnants in M3. But the dead stars are tough to find inside the crowded cluster.

Some of the stars of Messier 3 are more massive than the Sun. But they weren’t born that way. Instead, they’ve grown by cannibalizing companion stars.

Some of them have pulled gas off the surface of a companion. Others have merged with a companion. Either process adds to a star’s mass. That makes the star brighter and bluer – making it look a lot younger that it really is.

This huge cluster of ancient stars is about 34,000 light-years away. It’s in the constellation Canes Venatici, the hunting dogs. M3 isn’t quite bright enough to see with the eye alone, but it’s an easy target for binoculars. It’s well up in the east at nightfall, above the bright star Arcturus.

Script by Damond Benningfield

The Lucy spacecraft is headed for the Trojan asteroids – big chunks of rock and metal that share an orbit with Jupiter. But it’s checking out some other sights along the way. This weekend, for example, it’ll pass just a few hundred miles from a body in the asteroid belt, between the orbits of Jupiter and Mars.

Lucy is named for the fossilized remains of a human ancestor. The name was selected because the Trojans are fossil remnants of the early solar system. The mission’s current target is 52246 Donaldjohanson – named for the scientist who discovered Lucy half a century ago. The name was chosen after the asteroid was picked as a target for the spacecraft.

The asteroid is pretty small – only about two and a half miles in diameter. And Lucy will zip by at 30,000 miles per hour. So it won’t have long to study the target. But its pictures and other observations ought to tell us about the asteroid’s mass, shape, and composition.

Donaldjohanson is one of about 2,000 asteroids that are related – they were splintered off a parent body by a big collision. So Lucy’s encounter should tell us not only about Donaldjohanson’s history, but the history of its entire family.

This is Lucy’s second encounter with a member of the asteroid belt. After today, the craft isn’t scheduled to check out any other sights along the way. It’ll reach the Trojans in August of 2027.

Script by Damond Benningfield

A tight pair of stars got a lot tighter a few years ago. The stars merged, forming a single star. And it’s still settling into its new configuration.

V1309 Scorpii produced a brilliant outburst in 2008. At first, it was classified as a classical nova. Such an eruption occurs when a small dead star pulls gas from a close companion. When enough gas piles up, it causes a nuclear explosion.

Over the months after V1309 erupted, though, it became clear that something else had happened. The two stars had merged, forming a rare beast called a red nova. The merger produced a brilliant flash, and expelled lots of gas and dust at half a million miles per hour.

Continued study showed that the original stars were quite different. One was about half again as massive as the Sun, while the other was just half of the Sun’s mass.

Since the outburst, the system has gotten fainter and bluer. That could mean it’s becoming a blue straggler – a star that looks younger and brighter as the result of a merger. Or it could be headed toward a phase known as a planetary nebula – expelling its outer layers, leaving behind only a dead core. Astronomers continue to watch to see what happens.

V1309 is in Scorpius, which is low in the southern sky at dawn. Tomorrow, it’s just a tick to the lower left of the Moon. But it’s thousands of light-years away, so it’s too faint to see without a telescope.

Script by Damond Benningfield

If you look up the details of W Ursae Majoris, you’ll find that its two stars are about a million miles apart. The way astronomers figure that distance, though, is from the centers of the two stars. When you measure the distance between their surfaces, the stars are a whole lot closer. In fact, they’re touching. That makes them a contact binary – one of thousands discovered so far.

Many stars move through the galaxy with one or more companion stars. Their distances from each other vary greatly. Some can be light-years apart. But if they’re born close to one another, they might eventually spiral together. That might be caused by magnetic fields, the exchange of gas between the stars, or some other process.

W Ursae Majoris shows how that plays out. One of its stars is a little bigger, heaver, and brighter than the Sun. The other is about half the Sun’s mass. They’re in such close contact that they share their outer layers of gas. That makes them about the same temperature and color.

But they’re not the same brightness. As the stars orbit, once every eight hours, they cross in front of one other as seen from Earth. So the system’s brightness varies – the result of sibling stars in a tight embrace.

W Ursae Majoris is in the great bear, which includes the Big Dipper. The dipper is high in the sky at nightfall. W Ursae Majoris is well to the upper left of its upside-down bowl, and is visible through binoculars.

Script by Damond Benningfield

The most massive stars are seldom alone. Most of them have one or more companions – stars that are bound to each other by their mutual gravitational pull. Such stars were born together, from the same giant cloud of dust and gas. Dense clumps in the cloud collapsed and split apart, giving birth to heavy stars.

One possible example is Antares, the bright star that represents the heart of Scorpius. It stands close to the left of the Moon at dawn tomorrow.

The star we see as Antares is a supergiant. It’s more than a dozen times as massive as the Sun, and hundreds of times wider. If it took the Sun’s place in our own solar system, it would swallow the four innermost planets, including Earth.

Another big star accompanies the supergiant. It’s about seven times the Sun’s mass, and five times its diameter.

But it’s unclear whether the two stars actually form a binary. They move through space in the same direction and at the same speed. But they’re separated by more than 500 times the distance from Earth to the Sun – an especially wide gap. At that range, it would take up to a couple of thousand years for the stars to orbit each other. But we’ve only known about the smaller star for a few hundred years. That’s not long enough to trace any possible orbital motion.

So while the two stars probably form a binary, the case isn’t quite conclusive.

We’ll talk about some stars that are definite binaries tomorrow.

Script by Damond Benningfield

The Sun is an unusual star in several ways. It’s the only star known to support life. It’s in the top 10 percent of the most-massive stars in the galaxy. And it’s in the minority in another way: it moves through the galaxy alone.

Like all stars, the Sun probably was born in a cluster – a group of hundreds or thousands of stars. But the Sun’s birth cluster fell apart, with the stars going their own ways.

Most stars hang on to one or more of their siblings. Most of them form binaries – two stars bound by their gravity. Others form systems of three stars or more – all the way up to seven. The heavier a star, the more likely it is to have companions. For stars like the Sun, the odds are about 50-50.

The Sun has no companions today. But it could have in the distant past. In its crowded nursery, close encounters with other stars could have pulled the Sun and any possible companions away from each other.

Astronomers haven’t found any long-lost binary “twin” of the Sun. But they have found some stars that could have been born in the same cluster. A great example is HD 162826. Astronomers at McDonald Observatory found that its composition and motion are very close matches to the Sun’s.

HD 162826 rises above Vega, the brightest star of Lyra. They’re in the northeast in late evening. But you need binoculars to see this likely sibling to the Sun.

More about binaries tomorrow.

Script by Damond Benningfield

Orion is packed with stars that are much bigger, brighter, and heavier than the Sun. But only one of them is likely to draw hisses from Harry Potter fans: Bellatrix. Its name comes from Latin, and means “female warrior.” The name was applied to one of Harry Potter’s nastiest foes – Bellatrix Lestrange.

Regardless of its name, the star itself is impressive. It’s almost eight times the mass of the Sun, so it “burns” its nuclear fuel in a hurry. As a result, the surface of Bellatrix is tens of thousands of degrees hotter than the Sun. Combined with its great size, that makes the star thousands of times brighter than the Sun.

Because of its high-speed reactions, Bellatrix won’t live very long. The star is about 25 million years old – just half of one percent the age of the Sun. Yet it will expire in a few million years. It’s probably not massive enough to explode as a supernova. Instead, it will expel its outer layers in a more gentle process. That will leave a small, hot, dense corpse – a feeble ending for a powerful star.

Orion is in the west and southwest at nightfall. Look for its three-star belt, parallel to the horizon. The hunter’s brightest stars, Betelgeuse and Rigel, stand above and below the belt. Bellatrix is the next-brightest, to the upper right of the belt. It’s among the brightest stars in the night sky.

Script by Damond Benningfield