StarDate

The Small Magellanic Cloud is a satellite galaxy of the Milky Way. It’s about 200,000 light-years away, it contains hundreds of millions of stars, and it’s easily visible to the eye alone — from the southern hemisphere. And it may actually consist of two separate but related halves — two galaxies for the price of one.

Astronomers had suggested that possibility almost four decades ago. And a recent study provided the best evidence yet to support the idea. It found two large star-forming regions that are separated by about 15,000 light-years. One lines up in front of the other, making it hard to see them as individual objects.

A team studied the galaxy in several ways. It found that gas and dust are split into two distinct regions. Their material moves in different ways, and has a different composition.

The researchers also studied hot, young, bright stars. That also revealed two separate regions. And like the gas, the stars in the regions move in different ways, and have a slightly different makeup.

The team said the two regions could be remnants of two galaxies that came together long ago. On the other hand, the region that’s closer to us could be the main body of the galaxy. The region behind it then could be a tail of stars and gas pulled out by the gravity of the nearby Large Magellanic Cloud, which is bigger and heavier.

Either way, this close companion to the Milky Way may be more than meets the eye.

Script by Damond Benningfield

The heart of the lion stays close to the Moon the next couple of nights. The bright star that marks the lion’s heart is Regulus. It’s to the lower left of the Moon at nightfall this evening, and to the upper right of the Moon tomorrow evening.

Regulus is impressive. It’s a system of four stars, but only one shines bright enough to see. Known as Regulus A, it’s almost four times the Sun’s mass, and more than 300 times the Sun’s brightness.

But the Moon is even closer to another star of Leo that’s more impressive. Eta Leonis is to the upper left of Regulus. It looks fainter than Regulus. Under the glare of the nearby Moon, in fact, it can be hard to see — especially from light-polluted cities.

That’s only because Eta Leonis is much farther than Regulus — about 1800 light-years, versus only 79 light-years for Regulus.

In fact, Eta Leonis is a one-percenter — among the biggest and brightest stars in the galaxy. Studies show that it’s about 10 times heavier than the Sun, about 50 times wider, and about 20 thousand times brighter.

Eta Leonis is only about 25 million years old, compared to four and a half billion years for the Sun. But thanks to its great mass, the star is near the end of its life. Within a few million years, it’s likely to explode as a supernova. For a while, it will greatly outshine every other star in the galaxy — a brilliant beacon for the lion.

Script by Damond Benningfield

Two giants of the solar system huddle close together in the evening twilight the next few days. The viewing window is short, so you need to time it just right to see them.

Jupiter and Uranus are low in the west as twilight fades. Jupiter is easy to pick out — it looks like a brilliant star. Uranus is just above it tonight, by about the width of your finger held at arm’s length. But you need binoculars to pick it out. The planets will slide past each other on Sunday night.

Uranus is the Sun’s third-largest planet — four times the diameter of Earth. Its atmosphere is topped by an organic “haze,” which makes it tough to see much below it. The atmosphere consists mainly of hydrogen and helium. These elements are left over from the planet’s formation, from the cloud of gas that enveloped the young Sun.

The third-most-abundant member of the atmosphere is methane. It’s found mostly near the top of the atmosphere. Methane absorbs redder wavelengths of light, so Uranus looks like an almost featureless blue-green ball.

Methane is at least partially responsible for the high-altitude haze. Methane itself makes up part of the haze. The ultraviolet light from the Sun breaks apart some of the methane molecules. Their carbon and hydrogen then combine in different ways to make ethane, acetylene, and other compounds. So the haze is like the smog found over major cities — blocking much of this giant planet from view.

Script by Damond Benningfield

The star Arcturus is a little bit heavier than our own star, the Sun. Yet that small difference has a big effect on the star’s evolution: Arcturus entered a late stage billions of years earlier than the Sun will.

Arcturus is one of the brighter stars in the night sky, and shines yellow-orange. Both of those traits are a result of its stage in life, which was triggered by its mass.

Mass is the key to how quickly a star consumes the hydrogen in its core. The gravity of a heavier star squeezes its core more tightly, making it hotter. That revs up the star’s nuclear engine, causing it to “burn” through the hydrogen faster than a less massive star.

When the hydrogen is gone, the core shrinks and gets even hotter. The star’s outer layers then expand and cool, making its surface look redder. In technical terms, the star becomes a red giant.

And that’s what’s happened with Arcturus. So even though it’s only about eight percent more massive than the Sun, it’s 25 times wider and a couple of hundred times brighter. And its surface is cooler, so it looks redder than the Sun.

Arcturus is about seven billion years old. That’s older than the Sun, but not as old as the Sun will be when it becomes a giant: It won’t reach that stage of life until it’s more than 10 billion years old.

Look for Arcturus in the east at nightfall, and soaring high overhead during the night — a puffy star that’s nearing the end of its life.

Script by Damond Benningfield

The Moon creeps up on the twin stars of Gemini this evening. As night falls, Pollux and Castor are above the Moon. Pollux is on the left, and is a bit brighter than its “twin.”

There’s a lot more to Gemini than just the twins — or even the other stars that are visible to the unaided eye. In fact, one of its most intriguing objects produces most of its energy in the form of X-rays and gamma rays, which are far beyond the range of the human eye.

The object is known as Geminga — short for “Gemini gamma-ray source.” It was discovered in the 1970s, but it took decades for astronomers to figure it out.

Geminga is a neutron star — the dead core of a star that exploded as a supernova more than 300,000 years ago. It’s more massive than the Sun, but only about a dozen miles in diameter. That means it’s compressed to billions of times the density of ordinary matter.

Geminga rotates four times per second. As it spins, it sends out beams of energy — mostly gamma rays, the most powerful form of energy.

The dead star is racing through the galaxy at about 270,000 miles per hour. As it rams into gas in its path, material in a disk around the star is ripped away, forming a tail. At the same time, jets of particles that beam out from its poles form a double tail about half a light-year long. So Geminga is like a fast, heavy ship plowing through the interstellar sea, leaving a long, bright wake in its path.

Script by Damond Benningfield

This time of year is pretty inviting for some evening skywatching. The evening hours are warm but not usually too hot, and spring storm activity generally hasn’t reached its peak — pleasant conditions for watching the stars.

Unfortunately, one of the most beautiful star patterns is dropping from view, so there aren’t many more weeks to enjoy it.

Orion the hunter is low in the west as night falls. Its three-star belt stands almost parallel to the horizon. And its two brightest stars bracket the belt: orange Betelgeuse above, and blue-white Rigel below.

Orion climbs into prominence in the evening sky around Thanksgiving and Christmas. At that time of year, it’s in view for most of the night.

As the months roll by, though, so does Orion. The constellation rises earlier each night, so by late February, it’s halfway across the southern sky at nightfall.

And now, it’s about to drop from view. There’s only an hour or two of really good viewing time — between the end of twilight and the time Orion’s stars begin to set. And that viewing window gets shorter by the night. By mid-May, it’ll be hard to see the constellation at all.

Fortunately, though, there’s still a lot to look at after Orion passes from view. And the hunter won’t stay gone forever. He’ll begin to climb into the morning sky in August, and return to the evening sky during the longer, colder nights at year’s end.

Script by Damond Benningfield

Planetary systems can be violent. In our own solar system, for example, the Moon probably was born from the debris left over when a planet as big as Mars rammed into Earth billions of years ago. And the giant planet Uranus probably was knocked over on its side by a similar collision about the same time.

A more recent example comes from ASASSN-21qj — a star system that’s about 1800 light-years away, in the constellation Puppis.

In December of 2021, astronomers noticed that a Sun-like star there suddenly got a lot fainter. They kept an eye on the system, and also looked through records of its appearance in the past. They found that about two and a half years before it faded, the system grew a lot brighter, especially at infrared wavelengths.

A team recently reported a possible cause for all the changes: a massive collision between two planets. Both worlds probably were several times the mass of Earth. The impact made the system look brighter. And it produced a super-heated cloud of debris — gas, dust, and big boulders. This cloud then passed in front of the star, making the system look fainter.

In time, much of this debris could come together — making a new giant planet.

ASASSN-21qj is quite low in the south as night falls. It’s too faint to see with the eye alone. But it’s close to the brightest star of Puppis, so at least you can spot the location of this violent star system.

Script by Damond Benningfield

Planets like Earth live in the “Goldilocks zone” — the region around a star where conditions are most comfortable for life. But most planets aren’t so cushy. They’re either far away and cold, or close in and hot. And some are so close that they’re being vaporized by their star.

One example is WASP-69 b. It orbits a cool, faint star about 160 light-years from Earth. The system is in the constellation Aquarius, which is in the southeastern sky at dawn tomorrow.

WASP-69 b is only a few million miles from its parent star. At that close range, its atmosphere is heated to more than a thousand degrees Fahrenheit. The heat has caused the planet to puff up. While it’s only about a quarter as massive as Jupiter, the giant of our own solar system, it’s actually a little bigger than Jupiter.

That makes it easy for the star to blow away material from the planet’s atmosphere. That gives WASP-69 b a long “tail” like that of a comet. Recent observations found the tail is at least 350,000 miles long — greater than the distance from Earth to the Moon.

Even so, the rate at which the planet is vaporizing is pretty slow. It’s losing enough mass to make a planet as heavy as Earth every billion years or so. Considering that WASP-69 b is about 90 times the mass of Earth, this big, hot planet won’t disappear anytime soon.

We’ll have more about exoplanets tomorrow.

Script by Damond Benningfield

If you heat up some alphabet soup, you shouldn’t end up with all the letters clumped together — they should be fairly evenly spread throughout the pot.

According to the current understanding of the universe, the same thing should apply to galaxies. They may clump together on smaller scales, forming clusters and even super-clusters. But when you look at the universe as a whole, the galaxies ought to be evenly spread. Yet astronomers have found giant galaxy structures that seem to defy that idea — they can span billions of light-years.

Two recently discovered examples are the Big Ring and the Giant Arc. Both of them appear near the Big Dipper. And they may be related.

Both were discovered by a graduate student in England, who used a lot of computing power to produce 3D maps of galaxies. The Giant Arc was discovered first. It spans 3.3 billion light-years. The Big Ring was announced earlier this year. It is about 1.3 billion light-years across.

The galaxies in both structures are all about 9.2 billion light-years away. That means we’re seeing them when the universe was just one-third its current age. And the Giant Arc wraps around the Big Ring. The combination suggests the two are related.

So far, there’s no real explanation for these giant structures — nothing seems to fit all the observations. So scientists will keep on looking — trying to explain why the letters are clumping together in the cosmic alphabet soup.

Script by Damond Benningfield

Europa is one of the more intriguing bodies in the solar system — and one that scientists are especially eager to land a spacecraft on. The big moon of Jupiter may have a global ocean below its icy crust — an ocean that could host life.

But landing on Europa won’t be easy. It’s hundreds of millions of miles away, and it’s embedded in Jupiter’s powerful radiation belts. And the surface near its equator could be mottled by fields of icy spikes that are up to five stories high.

Such structures are known as penitentes, because they resemble penitent worshippers, on their knees. On Earth, they’re found in high, dry mountains. They’re carved as the Sun evaporates some of the ice, but not all.

A study a few years ago suggested that rough terrain near the equator of Europa could consist of similar fields. The spikes would be bigger than those on Earth — up to 50 feet high, and only about 25 feet apart.

Other studies disagree with that suggestion. We may find out for sure early in the next decade, when a mission to study Europa reaches the Jovian system.

Jupiter stands to the upper left of the crescent Moon early this evening. It looks like a brilliant star. Through binoculars, Europa and some of Jupiter’s other big moons look like tiny stars near the planet. And if you aim your binoculars a little above Jupiter, you can also spot the giant planet Uranus. The Moon will huddle closer to both planets tomorrow night.

Script by Damond Benningfield