StarDate

From most of the United States, Capella is the fourth-brightest star in the night sky. And it’s close by, too, at a distance of just 43 light-years. Yet until recently, we couldn’t see that Capella is actually two stars, not one. They’re so close together that even the biggest telescopes couldn’t show us the individual stars. Even so, by using astronomy’s full repertoire of techniques, those same telescopes did reveal a lot about the stars.

For example, astrometry, which measures the positions of astronomical objects, revealed that Capella is moving at more than 60,000 miles per hour relative to our own solar system.

Spectroscopy, which breaks light into its individual wavelengths, told us that the system consists of two stars. It also told us how quickly the stars orbit each other, what they’re made of, and how hot they are.

And photometry, which measures changes in brightness, revealed that even though the stars are close together, they don’t “bulge” out toward each other.

Astronomers combined these techniques to learn the masses of the two stars, and to discover that both stars are nearing the ends of their lives.

In recent years, new techniques have produced sharp images of Capella, finally showing us what astronomers have known for a long time: that Capella is two stars that shine as one in the night sky.

Capella is in the northeast at nightfall. It arcs high overhead later on, and is in the northwest at first light.

Script by Damond Benningfield

A pair of bright stars with an even brighter future is one of the highlights of the northern sky on late-autumn nights.

Capella, the brightest star of Auriga, the chariot driver, is in the northeast as night falls. The yellow star arcs high overhead after midnight, and is in the northwest at first light.

What looks like a single point of light is really two stars that are gravitationally bound to each other. They’re closer together than Earth is to the Sun, so even with giant telescopes it’s almost impossible to see them as individual stars.

Each star is at least two-and-a-half times as massive as the Sun, and a good bit bigger and brighter. And in the years ahead, they’ll get bigger and brighter still. That’s because both stars are nearing the ends of their lives. Now, they’re undergoing changes that are causing their outer layers to puff up.

Over time, each star should swell to dozens of times the size of the Sun, and shine hundreds of times brighter. Then the stars will blow off their outer layers, leaving behind their exposed cores, known as white dwarfs. But how that will play out is uncertain. As the first one puffs up, it will transfer some of its gas to the other, altering the evolution of both stars.

The clouds of gas around them will drag the two stars closer together. In the far distant future, they could slam together, creating a supernova — blasting both stars to cosmic dust.

We’ll have more about Capella tomorrow.

Script by Damond Benningfield

None of the thousands of planets found in other star systems is a good match for our own Earth. Even so, that doesn’t mean that it’s impossible for those worlds to harbor life. In fact, scientists have found that life can thrive in the most unlikely of places. Such organisms are known as extremophiles. And the first of them were reported in a study published 50 years ago today.

Thomas Brock was a biologist at the University of Indiana. He was studying life in pools of super-hot water at Yellowstone National Park. In 1965, he found mats of microscopic organisms at Octopus Spring, where temperatures were upwards of 175 degrees Fahrenheit. And the following year, he and a student found similar organisms in another hot spring. Before the discovery, conventional wisdom said that bacteria couldn’t survive temperatures above about 140 degrees.

Since then, scientists have discovered microscopic organisms in several extreme ocean environments. That includes both sub-freezing water, and super-hot water coming from mineral-rich vents on the ocean floor.

Other extremophiles have been found in layers of rock many miles deep. And a larger organism, known as a tardigrade, has survived days of exposure to the vacuum of space.

That doesn’t mean that life exists on any of the inhospitable planets that have been discovered. But it does mean that we can’t rule out the possibility of life in even the most unlikely of places.

Script by Damond Benningfield

John Mitchell was one of the most insightful scientists of the 18th century. He made important contributions to the study of earthquakes, magnetism, and other topics, including astronomy.

250 years ago, for example, he studied the Pleiades, the star cluster that marks the shoulder of Taurus, the bull. Telescopes of the day revealed a few dozen tightly packed stars. Mitchell calculated that the odds of finding so many unrelated stars in such a tiny volume were just one in 500,000. From that, he reasoned that the stars were bound together by their mutual gravitational pull. That made him the first scientist to suggest that the stars in a cluster are all related.

Mitchell was right. The Pleiades contains more than a thousand stars. All of them were born more than a hundred million years ago, from a single cloud of gas and dust. And today, they move through the galaxy as a family, bound by gravity.

That won’t always be the case, though. The gravity of the rest of the galaxy is tugging at the Pleiades, pulling some of its stars away. In about 250 million years, the cluster will have fallen apart, with its member stars orbiting the center of the galaxy on their own.

For now, though, look for the Pleiades low in the east as darkness falls, above the star Aldebaran, the bull’s orange eye. The cluster’s brightest stars form a tiny dipper. It crosses high overhead around midnight — a big stellar family that won’t stick together forever.

Script by Damond Benningfield

The heaviest stars in the universe eventually blast themselves to bits. But like a kicker getting ready to try a game-winning field goal, they first get in a few practice swings. These smaller explosions blast out shells of hot gas that expand at a million miles an hour.

One example is in Cassiopeia, the queen, whose brightest stars form a letter W. It’s well up in the north-northeast at nightfall.

Rho Cassiopeia is one of the biggest stars in the Milky Way — a yellow hypergiant. If it took the Sun’s place in our own solar system, it would extend past the orbit of Mars.

Rho Cassiopeia is probably a few dozen times heavier than the Sun. And it’s getting near the end of its life. Not long ago, it most likely was a red supergiant, so it was even bigger than it is now. But as a result of changes deep in its core, its outer layers are shrinking and getting hotter. As a result, the star probably will become a smaller and hotter blue supergiant.

These changes also trigger explosions on the surface of Rho Cassiopeia. An eruption in 2000 blasted out the equivalent of about 10,000 Earth masses of material — a half-century after a similar explosion.

More of these eruptions are probably in the star’s future. And eventually, it’ll blow itself apart as a supernova. Its outer layers will blast into space, while its core will be crushed — forming either a super-dense neutron star or an even denser black hole.

Script by Damond Benningfield

By the time the universe was a billion years old, something had given it a real charge. That “something” could be the first galaxies. And thanks to some help from cosmic magnifying glasses, astronomers have seen enough early galaxies to make that possibility more likely.

A few hundred thousand years after the Big Bang, electrons and protons began sticking together to make atoms of hydrogen. The atoms had no electric charge. By a billion years later, though, most of the hydrogen atoms had been split apart, giving them a charge. Learning what caused this can help astronomers better understand the early universe.

In a project known as the Hubble Frontier Fields, Hubble Space Telescope stared at several galaxy clusters for weeks at a time. The gravity of the immense mass in such a cluster acts as a magnifying lens, so it makes the galaxies that appear beyond the cluster look brighter. That revealed galaxies that were just one percent as bright as the galaxies that Hubble could see without it.

Astronomers at the University of Texas developed a way to remove the bright light from the cluster galaxies from the Hubble pictures. That allowed them to see the faint background galaxies — some of them up to 13 billion light-years away — among the first galaxies in the universe.

The images showed only a tiny fraction of the early universe. But they revealed enough distant galaxies to make it more likely that they gave the universe a charge.

Script by Damond Benningfield

The crescent Moon has a bright companion early this evening — the planet Saturn. It looks like a fairly bright star to the lower left of the Moon as darkness falls. They’re quite low in the sky, though, so any buildings or trees along the horizon will block them from view. They set not long after the sky gets fully dark.

Saturn is best known for its beautiful rings — thousands of rings in all. Most of them clump together in three wide bands.

The rings include several interesting features. Some of the rings are braided like a loaf of challah bread. Some aren’t complete rings at all. And at times, one of the main bands of rings shows dark “spokes” — radial features like the spokes of a bicycle wheel.

The spokes were first seen by the Voyager probes almost four decades ago. They were studied in detail by the Cassini orbiter, which ended its mission in September.

The spokes aren’t permanent features — they come and go. They disappear during the middle of Saturn’s winter and summer, but return around the equinoxes.

The spokes aren’t part of the rings themselves — they rotate at a different speed. The most likely explanation is that the spokes are made of tiny grains of dust. The particles acquire an electric charge, so they levitate above the rings, pulled along by Saturn’s magnetic field.

It’s not certain what causes the spokes to form. Whatever the cause, though, the spokes help make Saturn’s rings both beautiful and intriguing.

Script by Damond Benningfield

Our home galaxy boasts hundreds of billions of stars. Some of them emit lots of light, while others are dim. And tonight, the southern sky features a stunning contrast between two nearby stars: one powerful, the other feeble.

Both reside in the constellation Piscis Austrinus, the southern fish. If you look due south in early evening, you\'ll easily see the bright star, Fomalhaut. This white star is just 25 light-years from Earth.

Just south of Fomalhaut is another nearby star. In fact, Lacaille 9352 is even closer — a mere 11 light-years away. But you’ll never see it without some help, because the star emits only one percent as much visible light as the Sun does. So, close though it is, Lacaille 9352 is visible only through binoculars or a telescope.

Despite their vast difference in luminosity, both stars generate energy the same way: Nuclear reactions in their cores convert hydrogen into helium. But Fomalhaut was born with twice the mass of the Sun, so its center is hotter, making it burn brightly. In contrast, Lacaille 9352 was born with only half the mass of the Sun. So it’s faint, cool, and red — what astronomers call a red dwarf.

Red dwarfs may seem insignificant, but in one way they far surpass their brighter brethren: They account for about three-quarters of all the stars in the galaxy.

Script by Ken Croswell

November’s evening skies offer constellations with great names, intriguing back-stories, and beautiful star patterns. And then there’s Triangulum, which suffers from a distinct lack of imagination. As the name suggests, it consists of three main stars that form a triangle — an accurate if dull description for one of the smallest of all the constellations. It’s well up in the east as darkness falls.

The triangle is actually a thin wedge. And there’s an odd coincidence involving the stars at the base of the wedge: One of them is precisely third magnitude, while the other is precisely fourth magnitude.

Under the magnitude scale, a lower number means a brighter star. So the third-magnitude star is the brighter of the two — about two-and-a-half times brighter. Both stars are easily visible from dark skywatching sites, but are more difficult targets from the city.

The brighter star is Beta Trianguli. It’s a stellar giant about 127 light-years from Earth. The other, Gamma Trianguli, is a little smaller and closer. The star at the tip of the wedge, Alpha Trianguli, is even closer. It’s in the process of swelling up to become a giant.

Perhaps the most impressive feature in Triangulum isn’t a star at all, though. Instead, it’s M33, the Triangulum Galaxy. Through binoculars, it looks like a fuzzy star not far from Alpha. But that little smudge of light is actually a pinwheel of tens of billions of stars — three million light-years away.

Script by Damond Benningfield

Perseus, the celestial hero, stands well up the eastern sky by mid-evening on November nights. When we gaze that way, we’re looking toward the outskirts of the Milky Way galaxy.

Perseus harbors some amazing sights far beyond the Milky Way’s borders. That includes the Perseus cluster of galaxies, which is about 250 million light-years away. And astronomers recently discovered that the cluster is home to thousands of rogue star clusters — clusters that aren’t attached to any galaxy.

The star clusters are globulars, so named because each is shaped like a globe. A typical globular cluster packs hundreds of thousands of stars into a sphere just a few dozen light-years across. The Milky Way has about 160 known globular clusters, which look like glittering cities of stars.

The brightest galaxy in the Perseus cluster boasts an astonishing 13,000 globulars. But astronomers using Hubble Space Telescope recently discovered globular clusters between the galaxies. Each intergalactic star cluster probably once lived in a galaxy. As the galaxies skirted past one another, though, their gravitational pull yanked the star clusters away from their parent galaxies.

As a result, these orphan star clusters now drift homeless between the galaxies of Perseus. In all, the galaxy cluster has roughly 50,000 globular star clusters that have lost their homes — testimony to how the lives of galaxies can alter the lives of their stars.

Script by Ken Croswell