StarDate

Billions of years from now, our Sun will puff up to become an orange giant, shining hundreds or thousands of times brighter than it does now.

Orange giants are rare, but they’re so bright that they’re easy to see in the night sky. There’s one in the Big Dipper, for example, and the bright stars Arcturus, Aldebaran, and Pollux are orange giants as well.

Astronomers recently discovered a double orange giant in Sagittarius. The constellation is low in the south-southeast as night falls, and its brightest stars outline the shape of a teapot.

The recently discovered orange giants orbit each other once every nine months. They’re slightly farther apart than Mars is from the Sun. Each star is about five times as massive as the Sun. One of them is about 50 times the Sun’s diameter, while the other is even bigger.

The stars’ sizes and temperatures reveal how much light they emit into space. Comparing this with how bright they look indicates that they’re 7,000 light-years from Earth.

The two stars are much younger than the Sun — only about a hundred million years old. But because they’re so massive, they evolved quickly. They’ve converted the hydrogen in their cores into helium. Now, they’re converting the helium into carbon and oxygen — something the Sun won’t do for billions of years.

The details on these colorful stellar giants will yield new insights into the many orange giants that speckle the night sky.

Script by Ken Croswell

Our home galaxy is a spiral. We can’t see it from the outside, though, so we don’t know how its beauty compares with the many spirals we see elsewhere in the universe. But astronomers have discovered that one of the Milky Way’s spiral arms may wrap around the entire galaxy, hinting that our galactic home may be especially striking.

Spiral arms contain big clouds of gas that give birth to new stars. Astronomers in China listened for radio signals from this gas. They discovered 48 new clouds in the outer part of the galaxy that lined up with 24 previously known clouds. The clouds outline a previously unknown segment of a spiral arm. The segment spans 30,000 light-years.

The astronomers suggest that the segment may be part of a long arm called Scutum-Centaurus, after two constellations it passes through. The arm starts closer to the galaxy’s center than we are. The arm then winds outward, passing between us and the galactic center before reaching the other side of the galaxy. It then swings back toward our side of the galaxy.

If the new spiral-arm segment really is part of the Scutum-Centaurus arm, then it wraps around the entire Milky Way — a feat seen in few other spirals.

Centaurus is difficult to see from most of the United States, but Scutum is in good view right now. As night falls, it stands to the upper left of teapot-shaped Sagittarius. Under dark skies, you can see that it’s enwrapped in the hazy veil of the Milky Way.

Script by Ken Croswell, Copyright 2016

Two big, beautiful stellar families narrowly avoid the sting of the scorpion. They stand just above the stars that mark the scorpion’s stinger.

The families are the star clusters M6 and M7.

M7 is the brighter of the two, mainly because it’s only about half as far as M6. Each cluster contains perhaps a few hundred stars, spread across a dozen or more light-years.

Each cluster forms a tight-knit family. In both cases, the stars were born from a single giant cloud of gas and dust. The shockwave from an exploding star or some other event caused the cloud to collapse and split into smaller clumps of material. These clumps then collapsed more, eventually forming stars.

Today, the stars of each cluster remain bound together by their mutual gravitational pull. That means they circle the center of the Milky Way together — a family of stars sharing a ride around the galaxy.

To find the clusters, first find Scorpius. The constellation is quite low in the south at nightfall. Its brightest stars form a pattern that really does resemble a scorpion, with the head at the top and the tail to the lower left.

If you line up the two stars at the tip of the tail — the “stinger” — and extend that line to the upper left, you’ll come to M7. Under dark skies, it’s visible to the unaided eye as a hazy smudge of light. Slightly fainter M6 is to the upper right. Binoculars reveal many of the individual members of these beautiful stellar families.

Script by Damond Benningfield

The celestial scorpion has a potent stinger. The two stars at the end of its tail — the stars that mark the stinger — are bright, big, and heavy. And at least one of them is likely to suffer a sting of its own: it’ll explode as a supernova. In fact, it may explode twice.

The stars are known as Lambda and Upsilon Scorpii. Lambda is the brighter of the two, with Upsilon close to the right.

Upsilon is perhaps 10 or 11 times the mass of the Sun — quite hefty by stellar standards. And Lambda consists of at least three stars. The main star is a little heavier than Upsilon, while another is quite similar to Upsilon.

The stars of the stinger are probably just 10 million to 15 million years old — a tiny fraction of the age of the Sun. Yet they’re already nearing the ends of their lives. As they get closer to the end, they’ll puff up, getting much bigger and brighter.

Before long, though, each star will reach a stage where it can no longer produce nuclear reactions in its core. The core will collapse. Then, if the star is heavy enough, its outer layers will blast into space, forming a titanic explosion known as a supernova.

That’s almost certainly the fate of the brighter star of Lambda Scorpii. And depending on their exact masses, it could also be the fate of Lambda’s other bright star, and of Upsilon as well — creating a series of blasts that could briefly increase the “sting” of the scorpion.

More about the scorpion tomorrow.

Script by Damond Benningfield

Most of us are familiar with X-rays because doctors and dentists use them to diagnose problems with our bodies and teeth. But X-rays are also a natural phenomenon in the universe. And just as medical X-rays reveal details about our bodies, these natural X-rays reveal details about astronomical bodies.

An X-ray carries far more energy than visible light does. So X-rays often alert astronomers to extreme stars. In fact, the first black hole ever found gave itself away because gas falling into it emits X-rays.

But the brightest X-ray source outside our solar system isn’t a black hole. Instead, it’s a neutron star — the crushed core of a once mighty star. It’s only about a dozen miles across, but it’s more massive than the Sun. So if you could somehow stand on its surface, you’d weigh trillions of pounds. And if you dropped a pebble from a height of a few feet, it would smash into the surface at millions of miles per hour.

The neutron star is in the bright constellation Scorpius, which is in the southern sky on July evenings. In the 1960s, a rocket detected a source of X-rays there, so scientists named it Scorpius X-1 — the first source of X-rays in Scorpius. The X-rays come not from the neutron star itself, but from a disk of gas around it. The gas is heated to millions of degrees, so it produces X-rays.

Scorpius X-1 is the brightest X-ray source beyond our solar system — high-energy radiation warning spacefarers of an extreme star dead ahead.

Script by Ken Croswell, Copyright 2016

A beautiful and well-known constellation skitters low across the south on summer nights. It forms a distinctive hook shape, and its leading light is quite bright, so it’s easy to pick out. And it’s especially easy to find this year because two bright planets are just outside its borders.

Scorpius represents a scorpion, and it’s easy to see why. Several moderately bright stars outline a curving body that ends with a barbed stinger. And a row of stars at the top of the body forms the head. So once you find Scorpius for yourself, you won’t have any trouble coming back to it.

The scorpion’s brightest star is Antares — one of the most impressive stars in our region of the galaxy. It’s a red supergiant — it’s hundreds of times wider than the Sun, and tens of thousands of times brighter. But its surface is cooler than the Sun’s, so it looks bright orange.

Much of the scorpion’s body and tail are enwrapped in the glow of the Milky Way — the combined light of millions of stars in the disk of our home galaxy. And several bright star clusters reside within the constellation’s borders.

And right now, Mars and Saturn flank those borders. Saturn stands above Antares at nightfall. And even-brighter Mars is to the upper right of Antares, shining with the same orange color. In fact, that’s how Antares got its name. The name means “rival of Mars” — a name bestowed because its color is almost identical to the Red Planet’s.

More about Scorpius tomorrow.

Script by Damond Benningfield

Even as New Horizons flew past Pluto a year ago this month, mission planners were already thinking about a new destination. The spacecraft’s instruments were still working fine, it had plenty of power and fuel, and it was well into the distant Kuiper Belt, a realm that had never before been explored. So they pored over pictures from Hubble Space Telescope for a new object to study.

The one they picked is a chunk of ice and rock known as 2014 MU69. It’s no more than about 25 miles in diameter, and it’s a billion miles beyond the orbit of Pluto. At that great range from the Sun’s warmth, it should be the best-preserved solar system object yet studied — a relic from the birth of the planets.

If all goes well, New Horizons will fly just 2,000 miles from MU69 on January 1st of 2019. Along the way, it’ll conduct long-range scans of other objects in the Kuiper Belt. Among other things, it’ll look for moons and rings around those objects.

After that, New Horizons might spend another year or two looking at objects beyond the Kuiper Belt. And before the craft goes silent, a group wants to upload messages from Earth on its computer. The group is already looking at ways to get pictures, music, and other contributions from people around the world. It’s awaiting approval from NASA to start the project in earnest — a greeting card to other civilizations from the home world of a craft that explored the edge of the solar system.

Script by Damond Benningfield

At least four billion years ago, Pluto got smacked. Another icy body slammed into the little world, blasting a massive cloud of debris into orbit around Pluto. Over thousands of years, much of that material coalesced to form Pluto’s big moon Charon. And a few of the leftovers made four tiny moons.

Astronomers have long believed that such a “big whack” was responsible for the birth of Pluto’s moons. But confirming evidence was provided by New Horizons, a spacecraft that flew by Pluto one year ago this month. That evidence also provided the date for the collision.

New Horizons took sharp pictures of Charon and two of the smaller moons. Those images allowed scientists to count the number of impact craters on their surfaces. The greater the number of craters, the older the surface. In this case, the crater counts suggest that the moons formed at least four billion years ago.

New Horizons also found that the small moons are brighter than most of the objects in that region of the solar system, suggesting that they formed more recently, from fresher ice.

The New Horizons pictures also suggest that Charon originally had an ocean of liquid water below its icy crust. The ocean quickly began to freeze, which caused it to expand. That fractured parts of the crust, allowing liquid or slushy water to ooze onto the surface, forming relatively smooth plains — plains that have since been smacked by thousands of crater-forming impacts.

More tomorrow.

Script by Damond Benningfield

Pluto’s atmosphere is vanishing from sight. Much of it is freezing, adding new ices to Pluto’s surface. Over periods of millions of years, though, the atmosphere may get thick enough and warm enough to allow liquid to form on the surface — not water, but liquid nitrogen.

That’s among the many findings from New Horizons, a spacecraft that flew by Pluto last July. A year later, mission scientists have pieced together new details on Pluto’s atmosphere and surface, and on its history. But the picture is still incomplete. Because of Pluto’s great range, New Horizons won’t transmit the last of its readings to Earth until autumn.

So far, those readings have shown that much of the surface consists of frozen water — the equivalent of bare bedrock here on Earth. Some regions, though, are coated with ices made of nitrogen, methane, and carbon monoxide. These materials may periodically vaporize into the atmosphere, then condense on the surface as frost.

Over millions of years, Pluto’s tilt on its axis varies by quite a lot. That means the temperature varies as well. When Pluto is at its coldest, the atmosphere is quite thin. But when the little world warms up, the atmosphere gets much thicker — perhaps up to 30 percent as dense as Earth’s. Under those conditions, liquid nitrogen might flow across the surface, forming channels and ponds. In fact, New Horizons saw evidence of dry channels and frozen ponds on Pluto today — possible relics from a warmer past.

More tomorrow.

Script by Damond Benningfield

The Sun is a fairly big, middle-aged star. And as sometimes happens in those years, it moves a little more slowly than it did when it was younger — it takes almost a month to complete one full turn on its axis.

Many other stars spin much faster than the Sun does. An example is Altair, the brightest star of the constellation Aquila, the eagle.

Altair is almost twice as wide and heavy as the Sun. Yet despite its great bulk, it makes a complete turn in only about 10 hours. At that rate, a point at its equator moves at 130 miles per second — fast enough to cross from New York to Los Angeles in less than half a minute.

One reason Altair spins so fast is that it’s much younger than the Sun. The Sun probably turned much faster when it was young, too. But its magnetic field acts as a brake, slowing it down.

One of the effects of Altair’s high-speed rotation is that its gas is forced outward at the equator, making the star look a bit like a flattened beachball. It’s about 14 percent wider through the equator than through the poles. There’s a limit to how flattened the star can get, though; if Altair twirled about twice as fast as it does now, it would fly apart.

Altair forms the southern point of the bright Summer Triangle, which stands high in the east at nightfall. The highest and brightest point is the star Vega, with Deneb at the triangle’s left point. The triangle is still in view, high in the west, at first light.

Tomorrow: One year after Pluto.

Script by Damond Benningfield