StarDate

The Sun sometimes produces big outbursts of energy and particles. When they hit Earth, they can disrupt our technology. Fortunately, though, the Sun is quiet compared to some other stars. They can produce outbursts that are far stronger than anything we’ve seen from the Sun.

The activity on all stars is powered by magnetic fields. The layers of a star rotate at different rates. That creates an electric dynamo, which generates a magnetic field. Over time, the lines of magnetic force get tangled up. Eventually, they snap, then reconnect. That creates explosions of energy and eruptions of particles.

Young stars are the most active. They spin faster than older stars, so their magnetic fields are stronger — and so are their outbursts.

One study, for example, looked at a thousand “active” stars that are no more than five million years old — compared to four and a half billion years for the Sun. On average, these stars produce a flare at least a hundred thousand times as powerful as the strongest ever seen from the Sun every week. And they produce one that’s at least 10 million times the Sun’s best a couple of times a year.

But older stars can still be pretty active. A study of almost 400 Sun-like stars found that most of them produce bigger outbursts than the Sun does. That suggests that, while the Sun is quiet now, it might not stay that way. It could simply be in a lull — with more fireworks in the future.

More tomorrow.

Script by Damond Benningfield

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Many of the stars that sparkle across the night sky are deceptive — there’s much more to them than the eye can see. That’s because most of those points of light are the combined glow of two stars or more.

A famous example is Regulus, the bright heart of the lion. It stands close to the lower right of the Moon at nightfall, and below the Moon as they set, around dawn.

What we see as Regulus is a star that’s bigger and hotter than the Sun, and hundreds of times brighter. It has at least three companions. They’re all so faint, though, that they add little or nothing to the light we see from the system’s main star.

One of the companions is a white dwarf — the dead core of a star that once was more impressive than the visible star. It’s so close to the main star that it’s impossible to see through the glare.

The two other known stars also form a pair. They’re hundreds of billions of miles away from the bright pair. And they’re much fainter, so they’re visible only through a telescope.

The brighter member of this pair is a bit smaller, cooler, and fainter than the Sun. And its companion is cooler and fainter still — a bare cosmic ember that’s only a small fraction of the Sun’s brightness. The two stars are separated by about a hundred times the distance between Earth and the Sun. At that range, it takes them centuries to complete a single orbit around each other — under the glow of the star we know as Regulus.
 

Script by Damond Benningfield

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It’s impossible to tell how far a star is just by looking at it. The star Xi Puppis, for example, is fairly bright. That might suggest that it’s close by. Instead, it’s probably about 1200 light-years away — a long distance for a naked-eye star.

It’s hard to comprehend just how far that really is. A light-year is the distance that light travels in one year. Since it moves at a zippy 670 million miles per hour, the miles add up. So the distance to Xi Puppis is about seven quadrillion miles — a seven followed by 15 zeroes.

A star that’s that far away has to be especially bright, and Xi Puppis is. When you add up all the forms of light it produces, it’s about 60 thousand times brighter than the Sun. It’s also much bigger and heavier than the Sun.

But looking at this brilliant star is more than just looking across a vast distance. It’s also looking back in time. It takes the star’s light 1200 years to cross that gulf, so we see the star as it looked 1200 years ago — around the start of the ninth century.

Xi Puppis is one of the brighter stars of the constellation Puppis. It represents the stern of the ship Argo, which carried Jason and the Argonauts on their adventures. It sails low across the south this evening. Xi Puppis is visible from most of the country, quite low in the south at nightfall. It’s well to the lower left of Sirius, the brightest star in the night sky — just nine light-years from Earth.
 

Script by Damond Benningfield

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The big, bright constellation Orion scampers across the southwestern quadrant of the sky on March nights. It’s high in the sky at nightfall, just past due south, and doesn’t fully set until about 2 a.m. Look for its three-star belt. At nightfall, it’s flanked by bright orange Betelgeuse to the upper left, and blue-white Rigel to the lower right.

In mythology, Orion was a hunter. And one of the creatures he hunted stands just below his feet. Lepus, the rabbit, contains a few moderately bright stars. Their proximity to Orion makes them easier to pick out.

The brightest is Arneb. And it really is a bright star — more than 30,000 times brighter than the Sun. In fact, it’s impressive just about any way you look at it. It’s far bigger and heavier than the Sun, and it faces a more impressive fate — it will explode as a supernova.

Arneb is only about 13 million years old, compared to four-and-a-half billion years for the Sun. But because it’s so much more massive, it “burns” through the fuel in its core much more quickly. As a result, it’s already nearing the end of its life. Changes in its core have caused it to puff up — it’s big enough to extend to the orbit of Mercury or beyond if it took the Sun’s place.

Soon, it’ll get even bigger and brighter. Eventually, though, it will stop producing nuclear reactions in its core. The core will collapse, with the outer layers blasting out into space — giving the hunter a bit of a hotfoot.
 

Script by Damond Benningfield

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When a big space rock slammed into the southern hemisphere of the Moon about 110 million years ago, it created quite a mess. It gouged a crater that’s more than 50 miles wide and three miles deep. It sprayed out rock that created streaks up to a thousand miles long. And it even blasted material all the way to Earth — perhaps enough to form a thin layer across the entire planet.

The crater is known as Tycho. With its bright “rays” of debris streaking away from it, it’s visible to the unaided eye, and an easy target for binoculars.

A ring of darker material encircles the brighter crater. That’s probably glass — rock that melted during the impact that created the crater.

Apollo astronauts picked up samples from the rays, hundreds of miles from the crater itself. The robotic Surveyor 7 spacecraft landed inside the crater in 1967. NASA was considering sending Apollo 20 to Tycho as well, but the last three Apollo missions were scrapped, leaving the crater unexplored.

As much as 20 cubic miles of rock and dirt from the impact could have settled on Earth. A recent study looked for some of that debris in ocean sediments. It didn’t find as many likely samples as expected, but the search continues — for bits of the Moon here on Earth.

Tonight, look for the Moon near the bright twin stars of Gemini. The brighter twin, Pollux, is to the lower left of the Moon at nightfall, with slightly fainter Castor above Pollux.
 

Script by Damond Benningfield

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Last November, Mission Control had a scary message for the crew of the International Space Station.

MCC: We will need to activate Dragon safe haven and close center-line hatches for the next two crossings.

Russia had just blown up one of its own satellites with a missile. The explosion blasted fragments in every direction — some of them along the path of the station. A collision could cause severe damage and imperil the astronauts. So they put on their spacesuits and waited in their return capsules, just in case. They had to repeat the exercise later.

The space around Earth is filled with millions of objects — everything from space stations to tiny flecks of paint. And more pieces are added every day. That’s increasing the danger to both astronauts and robotic craft. It’s also costing time and money, as craft have to be maneuvered out of harm’s way.

There are thousands of big objects — satellites that are still working or that have expired. And projects like Starlink could add tens of thousands more over the next few years. Those craft are increasing the number of close encounters. China, for example, said that its space station had to dodge two Starlink satellites last year.

But space is also jammed with smaller objects — bits of exploded rocket stages and other debris. There are about a million pieces that are at least a centimeter across — big enough to cause major damage — adding to the hazards of the crowded space lanes.
 

Script by Damond Benningfield

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The old adage about truth being stranger than fiction certainly applies to astronomy. The universe is filled with strange stuff, from black holes to pulsars to dark matter. There’s also strange matter — a form of matter that may be forged under the extreme pressure found in the hearts of neutron stars.

A neutron star is the collapsed core of a supergiant star that exploded as a supernova. It’s more massive than the Sun but only as big as a city. A chunk the size of a sugar cube weighs a billion tons.

Under that incredible pressure, protons and neutrons may fall apart, leaving only their “building blocks,” known as up and down quarks. And if the neutron star is especially heavy, some of the down quarks could be transformed into strange quarks — the basic components of strange matter.

Like a virus, if any strange matter forms, it might quickly “infect” all the matter around it — converting everything to strange matter. So all but the crust of a neutron star could be made of strange matter — making it a strange star. If such a star rammed into a companion neutron star, it could become a strange star as well. And if the collision sent parts of the stars flying into space, they might form strange-matter planets.

No one has discovered any strange stars, although there are hints of strange planets. And strange matter is extremely hard to produce here on Earth. So we can’t be sure whether strange stars are truth or fiction.
 

Script by Damond Benningfield

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Many works of science fiction talk about the “galactic rim” — the outer edge of the Milky Way Galaxy. And the Moon points toward the rim the next couple of evenings. It will pass the star El Nath — the tip of one of the horns of Taurus, the bull. El Nath will stand above the Moon this evening, with the bull’s bright eye — the star Aldebaran — about the same distance below the Moon. El Nath will huddle closer to the Moon tomorrow night.

El Nath is near the galactic anti-center — the point opposite the Milky Way’s heart. So it points the way to the galactic rim and beyond.

The Milky Way forms a wide, flat disk. It’s more than a hundred thousand light-years in diameter. The solar system is roughly half way out from the center to the rim.

The center is thicker than the rest of the galaxy. It’s packed with stars, gas clouds, and black holes. As you approach the rim, though, things are much more open — like the deserts of the southwest compared to the city of Los Angeles. There are fewer stars, and less gas and dust. There’s no precise boundary that marks the edge, though — the galaxy just fades away.

The rim forms a ring around the entire sky. The circumference of that ring is hundreds of thousands of light-years. But El Nath points the way to the rim’s closest point.

There are still a few stars and puffs of gas and dust outside the rim. But they’ve escaped from the Milky Way — flying beyond the edge of the galaxy.
 

Script by Damond Benningfield

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The Moon slides across the body of Taurus, the bull, tonight. It’s roughly half way between his face and shoulder.

Both features are outlined by star clusters. The face is outlined by the Hyades, which forms a “V.” The bright orange star Aldebaran represents the bull’s eye, at one point of the V. It’s not part of the cluster, though — it’s only about half as far away.

The shoulder is marked by the Pleiades — a sparkly collection of stars that looks like a small dipper.

The Hyades is the closest of all star clusters — just 150 light-years away. It consists of a few hundred stars. They’re packed together in a ball that’s about 65 light-years across.

The cluster actually contains more stars outside that zone. But they’re barely holding on. They’re being tugged by the gravity of some of the Milky Way’s giant clouds of gas and dust, as well as its spiral arms. In another hundred million years or so, most of the stars of the Hyades will have been pulled away, and the cluster will cease to exist.

The Hyades is about 625 million years old. The Pleiades, on the other hand, is just 115 million years old. It’s about three times farther than the Hyades, and about twice as massive — it contains at least a thousand stars. Yet it, too, is being pulled apart. As the Hyades fades away, so will the Pleiades — leaving the bull without his prominent face and shoulder.

More about the Moon and Taurus tomorrow.
 

Script by Damond Benningfield

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The more scientists try to break down Albert Einstein’s theory of gravity, the stronger it looks. An experiment that kept an eye on a pair of extreme dead stars, for example, confirmed several of its predictions.

The theory is General Relativity. Einstein presented it in 1915, and it’s withstood every test since then. Yet scientists know that it must break down at the tiniest scales, or inside objects like black holes. They’re pushing to find its limits.

The new experiment spent 16 years watching the Double Pulsar — two dead stars in a tight orbit around each other. A pulsar is the crushed core of a once giant star. It spins rapidly, beaming energy into space like a lighthouse. Telescopes on Earth record each “pulse” of energy.

The Double Pulsar is about 2400 light-years away. Each of its stars is heavier than the Sun, but only the size of a city. One of them spins about three times per second, the other about 45 times per second.

Astronomers used radio telescopes all across Earth to watch the stars. The results showed that the pulsars are moving closer together. That confirms that they’re producing gravitational waves — ripples in space-time — just as relativity predicts.

The study also measured how the pulsars’ gravity affects the way light waves move, how the pulsars affect the flow of time, and more. The results all matched relativity’s predictions — more confirmation of Einstein’s theory of gravity.
 

Script by Damond Benningfield

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