StarDate

There’s no fountain of youth to make people look younger. But there is one for stars. It’s a process that sounds like a story from a 1950s B movie — “stealing” life from another star.

A good example of a rejuvenated star is in the constellation Fornax, which is low in the south as night falls. It has only one modestly bright star, Alpha Fornacis, which is 46 light-years away.

To the eye alone, it’s not much to look at. Binoculars, though, reveal that it consists of two stars. One of them is bigger and heavier than the Sun. It’s nearing the end of its life, even though it’s almost two billion years younger than the Sun.

The other star of Alpha Fornacis is smaller than the Sun, and its surface is cooler than the Sun’s, so it glows orange. Yet it should be even redder than it is. And that’s where the story of rejuvenation comes in.

The star has been identified as a blue straggler. That means its color shifted to slightly bluer wavelengths as the star aged. It might have done so by merging with another star, which would rev up its nuclear reactions, making it hotter and bluer. On the other hand, it might have changed color by simply stealing gas from a third star in the system.

And there is some evidence of a third member of Alpha Fornacis — the corpse of a once-normal star. If it’s there, it may be about half as massive as the Sun, and quite close to the blue straggler — a dead star that gave part of its life to a stellar companion.

Script by Damond Benningfield

Almost a century ago, astronomers partitioned the celestial sphere into 88 constellations. Most of them — the famous ones — date from ancient times. But 14 of them — none of which is famous — were created by a single man, in the 18th century.

Nicolas Louis de la Caille was a French astronomer. In 1751, he set up an observatory at the Cape of Good Hope in South Africa to study the stars of the southern hemisphere. Over the following year, he cataloged about 10,000 stars. And later, he used those stars to draw new constellations in regions of the sky that weren’t visible from most of Europe.

He called one of them Mons Mensa — table mountain. It honored a feature near la Caille’s observatory. He named all the others for tools that had scientific uses, such as the telescope and microscope, or artistic uses, such as the painter’s easel.

One of those constellations is Fornax, the furnace, which is quite low in the south as night falls right now.

It was originally called Fornax Chemica, after a small heater that was used for chemistry experiments. Another astronomer shortened the name a few decades later.

Fornax isn’t much to look at — at least not with the eye alone. It contains only one modestly bright star, Alpha Fornacis, which we’ll talk about tomorrow. But a telescope reveals many treasures within its borders, including some beautiful individual galaxies, plus a giant cluster of galaxies — fiery visions in the celestial furnace.

Script by Damond Benningfield

When astronomers find a new type of object that goes “boom,” it takes a while to explain it. They have to figure out how far away the objects are, which reveals how bright they are. And they have to see them at different wavelengths to understand what they’re doing.

They’re just starting that process for a class of objects known as fast radio bursts — blasts of radio waves that last no more than a few thousandths of a second. The first was discovered in 2007, and a few dozen others have been seen since then.

Theorists have proposed several explanations for the bursts — from mergers between stellar corpses, to flares on the surfaces of highly magnetized corpses.

The effort to understand them has been stymied because astronomers hadn’t seen any of the bursts at other wavelengths. But that changed with a burst that was discovered in November of 2013.

A space telescope was looking at the same region of sky where the radio burst was discovered. An analysis, reported late last year, showed that the burst was accompanied by a blast of gamma rays, which are produced by some of the most violent events in the universe.

That means that this particular burst took place far outside our home galaxy, so it had to be extremely energetic. That eliminates some possible explanations for the burst. But astronomers say that different bursts could have different causes. So it’ll take a while to fully understand the diverse nature of fast radio bursts.

Script by Damond Benningfield

A supernova that was discovered a couple of years ago has astronomers doing a lot of head scratching. The explosion appears to be a couple of hundred times brighter than a typical supernova. But none of the models of how stars explode can fully explain why the blast was so bright.

Supernova 15LH is thought to be the violent death of a massive star. Such a star dies when it can no longer produce energy in its core. The core collapses, and the surrounding layers are blasted into space.

It’s not easy to explain a blast as powerful as 15LH, though — but that hasn’t stopped the theorists from trying.

One team, for example, says that the energy could be coming from the interaction between the supernova blast wave and a shell of gas and dust around the star. The material would have been expelled from the star long before the explosion, and was moving away from the star.

Other groups have come up with other ideas. One says that the supernova was powered by a magnetar — the star’s collapsed core. The super-dense, highly magnetized core would be spinning about a thousand times per second, pumping energy into the material around the core with each turn.

And yet another idea says that 15LH wasn’t a supernova at all. Instead, it was the death throes of a star that was ripped apart by a supermassive black hole.

With all these competing ideas, it’s likely to take a while to explain Supernova 15LH.

We’ll talk about another stellar blast tomorrow.

Script by Damond Benningfield

Every supernova is a brilliant beacon — a stellar explosion that can outshine an entire galaxy. But in recent years, astronomers have logged a few dozen supernovae that take “brilliant” to extremes — they shine anywhere from about 10 to hundreds of times brighter than a typical supernova. And theorists are still trying to understand why.

The first examples of “superluminous” supernovae were discovered more than a decade ago by Robert Quimby, a graduate student at the University of Texas at Austin. He was looking for supernovae across large patches of the sky when he discovered a couple of exceptionally bright examples. Since then, other astronomers have joined the search, leading to many new discoveries.

These super-bright explosions appear to come in two varieties. One contains a lot of hydrogen — the element that makes up the bulk of most stars. The other type shows no hydrogen.

The hydrogen-rich variety may involve a shell or bubble of hydrogen gas around the star that was expelled from the star before it exploded. If the bubble has expanded to just the right size, then the collision with the debris from the supernova could make it extremely hot. At such high temperatures, it would radiate enormous amounts of light — making it a superluminous supernova.

The hydrogen-poor variety is a bit more mysterious. Theorists have proposed several explanations — from the magnetic cores of dead stars to stellar encounters with black holes. More about that tomorrow.

Script by Damond Benningfield

Astronomers compile catalogs of all kinds of objects: variable stars, black holes, binary stars, and many others. One of their most important catalogs keeps getting bigger — it passed 15,000 entries a couple of months ago.

The catalog lists N-E-Os — Near-Earth Objects. These asteroids and comets follow paths that approach or cross Earth’s orbit around the Sun. Such objects have the potential to hit our planet, so it’s important to find and track them. With enough warning, it might be possible to deflect an object that’s on a collision course.

Most of that work is done by automated searches in Arizona and Hawaii, which scan the sky most clear nights of the year. A new search is scheduled to begin next year in Europe, with another, using a giant new telescope in Chile, to follow soon after.

Scientists estimate that they’ve found more than 90 percent of NEOs that are at least a kilometer in diameter. Such giant space rocks could cause widespread damage if they hit us. In fact, just such an impact is thought to be responsible for the demise of the dinosaurs.

In recent years, searchers have been looking for even smaller objects. Such objects wouldn’t be big enough to trigger global problems if they hit, but they could destroy a city. But smaller objects are also fainter, so it takes much more effort to find them.

So far, the searches haven’t discovered any problems — none of the 15,000 cataloged NEOs is on a threatening course.

Script by Damond Benningfield

Regulus is one of the brightest stars in the night sky, so people have been looking at it since the beginning. And astronomers have been studying it since the invention of the telescope. And it’s quite close — less than 80 light-years away. So you might think that we’ve known all the important details about it for a long time.

You’d be wrong. Astronomers continue to learn about the system. Less than a decade ago, for example, they found that the bright star we see as Regulus has a close companion. That star tells us a lot about the bright star’s history.

The companion is small, faint, and quite close to the bright star, which is known as Regulus A. So it’s impossible to see the companion directly. Instead, astronomers detected it by measuring the system’s individual wavelengths of light. They reveal a slight shift in the star’s motion caused by the gravitational tug of the companion.

The companion is a white dwarf — the tiny corpse of a once-normal star. That star had to be born with more mass than Regulus A, so it aged faster. It puffed up, then dumped much of its outer layers of gas onto Regulus A. That made Regulus A bigger and hotter, and it made the star spin much faster.

That discovery shows that there’s still a lot to learn about the stars — even the ones we think we know well.

Look for Regulus just above the Moon as they climb into view in mid-evening, and a little farther to the right of the Moon at first light tomorrow.

Script by Damond Benningfield

The structure of the universe is like a Russian matryoshka doll — each bit is nested inside a larger one. In our case, for example, Earth is a member of the solar system, which in turn is a member of the Milky Way galaxy, which is a member of a family of galaxies known as the Local Group.

And the nesting doesn’t end there. The Local Group is a member of a much larger collection of galaxies known as the Local Supercluster. It spans more than a hundred million light-years, and contains tens of thousands of galaxies.

The supercluster was discovered and named more than half a century ago, by Gerard de Vaucouleurs. It’s centered roughly on the Virgo Cluster, which contains a couple of thousand galaxies.

Most of the supercluster’s galaxies appear to form a flat disk, with a few in a wide halo around the disk.

The mass of all these galaxies is equal to a million billion Suns. But most of that mass is invisible. Instead of glowing stars and gas clouds, it consists of dark matter — material that produces no detectable energy, but that exerts a gravitational pull on the visible matter around it. It may consist of subatomic particles, although physicists have had a hard time finding them.

The nested dolls may not end with the Local Supercluster, though. A study a couple of years ago found that it may be part of an even bigger supercluster — one that spans half a billion light-years — one more layer in the structure of the universe.

Script by Damond Benningfield

The Milky Way is doomed. Our home galaxy will collide with the Andromeda galaxy. The collision will scramble both of them, ejecting many of their stars. The two galaxies will then merge — and the Milky Way as an individual galaxy will be no more.

Andromeda and the Milky Way are the biggest members of the Local Group, a small family of galaxies. Both are giant spiral galaxies that contain hundreds of billions of stars.

Right now, they’re about two and a half million light-years apart. But they’re caught in each other’s gravitational grip. So every hour, they move about a quarter of a million miles closer — the distance from Earth to the Moon.

As they get closer, their approach will accelerate. In about four billion years, the galaxies will ram together. Individual stars are so widely spaced that collisions between stars are unlikely. But the gravity of all the stars and gas clouds will stir things up. It’ll eject big streamers of stars from the galaxies, and cause clouds of gas and dust to slam together, giving birth to millions of new stars.

Over the following billion years or so, Andromeda and the Milky Way will merge to form a single galaxy — one of the most impressive in all the cosmos.

Andromeda is pretty impressive even now. From a dark skywatching location, it’s visible to the unaided eye. It looks like a tiny smudge of light. At this time of year, it’s high in the west as night falls — a glimpse at our galactic future.

Script by Damond Benningfield