StarDate

The universe is filled with brilliant black holes. They shine like beacons, visible from billions of light-years away. And they fire “particle beams” toward Earth — jets of hot gas moving at almost the speed of light. They’re called “blazars.”

These supermassive black holes inhabit the cores of galaxies. And just to be clear, it’s not the black holes themselves that are bright. Black holes are completely dark — they emit no light of any kind.

But a black hole’s gravity pulls in gas, dust, and stars. The material spirals around the black hole at high speed, forming a disk. Friction in the disk heats it to millions of degrees, so it shines brighter than entire galaxies of stars.

So far, that description also fits another class of objects, known as quasars. What sets a blazar apart is a jet of super-heated gas, known as plasma, shooting away from the poles of the black hole.

Heat inside the disk rips atoms apart, giving the material an electric charge. Powerful magnetic fields in the disk scoop up some of the charged particles before they can disappear into the black hole. They shoot the particles into space at just below lightspeed. If one of the beams happens to aim toward Earth, it makes the object look especially bright — a blazar.

Astronomers have located thousands of them, with more joining the lineup all the time — bright black holes taking aim at Earth.

More about black holes tomorrow.
 

Script by Damond Benningfield

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The Moon has a couple of bright companions tonight and tomorrow night. The brighter one is the giant planet Saturn, which looks like a bright star close to the upper left of the Moon as darkness falls this evening. The other is the star Fomalhaut. It’s farther to the lower left of the Moon, and it’s only about half as bright as Saturn. But it’s the only noteworthy star in that region of the sky, so it’s hard to miss.

For more than a decade, it looked like Fomalhaut might have a giant planet of its own. Hubble Space Telescope took pictures of it — a tiny dot of light far from the star. And astronomers even gave it a formal name: Dagon.

But a few years ago, the dot of light spread out, then faded from sight. That means the object probably was a giant cloud of dust. When Hubble first saw it, the cloud had just formed — probably debris from a collision between two asteroids. Over the years, the dust spread out. Eventually it became so thinly spread that we could no longer see it.

Even so, it’s possible that Fomalhaut could have one or more planets. A disk of gas and dust encircles the star. Voids within the disk could have been swept clean by orbiting planets. In addition, the gravity of planets could account for some “clumpy” regions in the disk. So far, though, these are only suggestions that Fomalhaut has planets. The worlds themselves — if they exist at all — still await discovery.
 

Script by Damond Benningfield

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A star system in Hercules almost seemed embarrassed. A couple of years ago, it grew thousands of times brighter in just a day or so. But then it started returning to normal faster than any system of its type yet seen.

V1674 Herculis is a binary — two stars locked in orbit around each other. One of the stars is a white dwarf — the dead core of a once-normal star. The other is in the prime of life. The two stars are so close together that the white dwarf pulls gas from its companion. As the gas piles up on the white dwarf, it’s heated and squeezed. In June of 2021, that triggered an explosion — a nova.

It usually takes weeks for such an eruption to fade by much. But V1674 dropped to a small fraction of its peak brightness in just a couple of days.

A recent study suggested that the gas that stacked up on the white dwarf mixed into the dead star. That triggered a nuclear explosion below the surface, blasting out material at two percent of the speed of light.

But not all of the gas erupted into space. Some remained on the white dwarf, adding to its mass. In fact, the star is so massive that it may be building up to a much bigger explosion. The star might blast itself to bits as a supernova — an outburst that will really draw attention.

V1674 Herculis is along the border between the constellations Hercules and Aquila. The system is high in the southwest at nightfall, but you need a telescope to see it.
 

Script by Damond Benningfield

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Many searches for planets in other star systems look for stars like the Sun. Since the Sun is the only star that’s known to harbor life, that makes sense.

But Sun-like stars are pretty rare. So some searches are taking aim at stars in the next category down — stars that are a little smaller, lighter, and fainter than the Sun. They’re known as K dwarfs. They’re in the prime of life. And they can stay in that phase for tens of billions of years — much longer than the total lifespan of the Sun. That means there’s plenty of time for life to take hold in such systems.

And the systems should be good homes for life. The stars are pretty stable, and they don’t produce a lot of damaging radiation. And they’re good targets for planet hunts because habitable worlds are likely to be fairly close to their stars, making them easier to find.

Astronomers have mapped about 5,000 K dwarfs within 50 parsecs of Earth — about 165 light-years. A few dozen of them have confirmed planets. But none of the planets is like Earth, or in the right place for Earth-like life.

A double K-dwarf system is high in the sky at nightfall, less than 12 light-years away. It’s close to Deneb, the bright tail of Cygnus, the swan. The system’s two stars are far apart, so there’s plenty of room for planets. So far, though, no planets have been found — prime real estate with no tenants.

Tomorrow: the brilliant “morning star” stands high.
 

Script by Damond Benningfield

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The surface of Comet Halley is being peeled away like the skin of an onion. It loses a layer about three to 10 feet thick every time it passes near the Sun. And that’s good news for skywatchers. Earth intercepts some of that debris every October, creating the Orionid meteor shower. The shower should be at its best the next couple of nights.

Halley is a slab of ice, rock, and dust that’s about nine miles long. It comes closest to the Sun every 75 years or so. The Sun warms the surface, vaporizing some of Halley’s frozen water and other ices. The vapor spews into space, carrying some of the rock and dirt along with it.

Over time, the material spreads out along the comet’s orbit, forming long, skinny clouds of debris. A new streamer forms with every close approach. Some of them are wider and thicker than others.

Earth intersects Halley’s orbit every October. Bits of comet dust slam into the upper atmosphere at almost 150,000 miles per hour. The debris quickly vaporizes, forming the streaks of light known as meteors.

The shower should be at its best tonight and tomorrow night, after midnight. Under clear, dark skies, you might see a dozen or more meteors per hour. If you trace their paths across the sky, all of them appear to “rain” into the atmosphere from Orion — hence the shower’s name. But the meteors can blaze across any part of the sky — the remnants of a slowly disappearing comet.
 

Script by Damond Benningfield

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Characters in Greek mythology never seemed to learn that it was a bad idea to disrespect the gods. Consider Cassiopeia, the queen of Ethiopia. Her vanity led to all kinds of trouble with the gods — and eventually got her placed in the stars.

Cassiopeia was a great beauty. But her trouble started when she boasted that she was more beautiful than a group of sea goddesses known as the Nereids. They didn’t like the put-down at all, and they plotted revenge.

One of them was married to the sea god, Poseidon. As a punishment, he sent the monster Cetus to ravage the coast of Ethiopia. To appease him, Cassiopeia and her husband, King Cepheus, chained their young daughter Andromeda at the shore as a sacrifice.

Before Cetus could get her, though, she was rescued by Perseus, who killed the monster. Perseus and Andromeda were married and, according to most versions of the tale, lived a long and happy life together.

Cassiopeia’s punishment wasn’t over, though. In fact, it’s still going on. The gods placed her in the stars, where she wheels around the North Star. Part of the time she sits upright, but part of the time she hangs upside down — one last indignity for disrespecting the gods.

Look for Cassiopeia well up in the northeast at nightfall. She’s easy to find because her brightest stars form a letter M or W. The constellation wheels high across the north after midnight.

Tomorrow: remnants of a disappearing comet.
 

Script by Damond Benningfield

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The scorpion is vanishing in the evening twilight. But tonight offers one last good chance to see it. Antares, the scorpion’s bright “heart,” is close to the Moon. They drop from sight not long after the sky gets good and dark.

Antares is one of the biggest and brightest stars in our region of the galaxy. It’s at least a dozen times the mass of the Sun. And it’s so large that if it took the Sun’s place, it would engulf the four inner planets, including Earth.

Antares is only about two or three percent of the Sun’s age. But because of its great mass, its time is about up. Within the next million years or so, it should explode as a supernova. It’s about 550 light-years from Earth, so it’s no threat to our planet. But it will have an impact on the space around it: The explosion will clear out much of the gas and dust that’s close to Antares, creating a big “bubble” in space.

The scorpion’s heart belongs to a group of stars known as the Scorpius-Centaurus Association. It includes many stars that are similar to Antares. As they explode over the next few million years, they’ll also clear away the surrounding material. The combination of many exploding stars could form a giant bubble similar to the one that encompasses the solar system.

The stars also will “seed” the surrounding space with heavy elements. Those elements could be incorporated into future stars and planets — creation from the deaths of stars.
 

Script by Damond Benningfield

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Our home galaxy, the Milky Way, is a bit like the foam on top of a bubble bath — bubbles, bubbles everywhere. Some are giant, some are tiny. And like a bubble bath, the bubbles come and go. New ones form, while others “pop.”

One of them is the Local Bubble. It spans dozens of light-years. It incorporates our solar system and many nearby stars — some of which were born as a result of the bubble’s formation. The bubble probably was inflated by several supernovas — exploding stars that swept away the gas and dust around them.

There are smaller structures within the Local Bubble. One of them is the Local Interstellar Cloud. It’s about 30 light-years across. The solar system is near its edge — just inside the cloud, or along the boundary with an adjoining cloud.

The cloud is a little bit denser than the rest of the Local Bubble. But it’s much less dense than the galaxy outside the bubble — an indication that it, too, was influenced by supernovas.

The cloud is moving away from the Scorpius-Centaurus Association — a nursery that’s given birth to thousands of stars, including many that are big, bright, and heavy. Winds from these stars may add material to the cloud, while pushing the cloud outward. Some of the stars will explode fairly soon. Their blast waves could clear out all or part of the Local Interstellar Cloud — creating new bubbles in the Milky Way.

We’ll talk about one of those future supernovas tomorrow.
 

Script by Damond Benningfield

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A giant “bubble” surrounds our solar system. It’s kept puffed up by the Sun, and it extends far into space. In fact, scientists recently came up with a new estimate of the bubble’s extent: a thousand times the distance from Earth to the Sun.

The bubble is known as the heliosphere. It’s created by the Sun’s magnetic field. A flow of charged particles known as the solar wind streams into space along the lines of magnetic force. As the Sun rotates, the streams spin around like ribbons of water from a lawn sprinkler.

Eventually, the solar wind gives way to particles from interstellar space — the boundary of the heliosphere.

The Voyager 1 and 2 spacecraft have been probing the boundary. The craft are farther from the Sun than any other spacecraft in history. Their observations indicate that they’re in a transition zone. The interstellar magnetic field drapes around the heliosphere like water flowing around the bow of a ship.

Scientists recently combined readings from the Voyagers with those from IBEX — a satellite in Earth orbit that looks for the boundary of the heliosphere. Their work suggests that the transition zone may extend a thousand times the Earth-Sun distance — about a hundred billion miles.

The Voyagers won’t live long enough to reach that boundary. But other probes — in Earth orbit and beyond — should help scientists map the exact extent of the heliosphere.

We’ll talk about an even bigger bubble tomorrow.
 

Script by Damond Benningfield

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Charles Messier compiled a catalog of “fuzzy” objects in the night sky to help his fellow astronomers discover more comets. But it was while watching a comet that Messier discovered the 51st object on his list.

He found it 250 years ago tonight. He described it as “a very faint nebula, without stars.” Modern telescopes see it as a beautiful spiral galaxy, known as the Whirlpool. It’s about 25 million to 30 million light-years away. It’s a little smaller than our own galaxy, the Milky Way.

M51 actually consists of two galaxies that have sideswiped each other. The close encounter helped create the larger galaxy’s beautiful spiral arms.

The gravity of the smaller galaxy, which looks like a bright knot of stars at the end of one of the larger galaxy’s spiral arms, has created waves that roll around the galaxy’s core. The waves compress clouds of gas and dust, triggering the birth of new stars. Some of the new stars are big, hot, and bright, so they outline the spiral arms.

These young, bright stars don’t last long, though — they explode after a few million years. In fact, three stellar explosions have been seen in M51 in the past few decades, compared to none in the bigger Milky Way. Even as they die, though, the stars are replaced by new ones — the offspring of a galactic encounter.

M51 is just outside Ursa Major, near the tip of the Big Dipper’s handle. It’s an easy target for small telescopes.
 

Script by Damond Benningfield

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