StarDate

A black hole that formed from the merger of two smaller ones may have kicked itself out of its home galaxy.

The merger happened in a galaxy about three billion light-years from Earth. That was too far to see with normal telescopes. But the merging black holes produced a huge outburst of gravitational waves — tiny ripples in space-time. Detectors “heard” the merger in early 2020, so it was cataloged as GW200129. Scientists converted the waves to sound, and slowed them down a bit to reveal the merger.

The signal revealed important details about the merger. It told scientists that the original black holes had a combined mass about 75 times that of the Sun. The merger produced a single black hole about 60 times the Sun’s mass. The rest of their mass was converted to gravitational waves.

Computer models indicated that the two black holes had different masses and spins. Because of that, the gravitational waves fired off mainly in one direction. That pushed the black hole in the opposite direction.

The black hole probably was kicked at more than three million miles per hour. The scientists don’t know anything about GW200129’s home environment — what kind of galaxy it lived in, or if it was in a cluster inside the galaxy. Regardless, that should be fast enough for the black hole to escape most galaxies and zip into intergalactic space — a swift kick provided by the black hole itself.
 

Script by Damond Benningfield

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The universe can fool you. Objects that look like they’re close together can be a good distance apart. And it can take a lot of time and effort to figure that out.

An example is the Cocoon Nebula. It’s a glowing cloud of gas and dust in Cygnus, the swan. It’s half way up the northeastern sky at nightfall, below Deneb, the bright star that marks the swan’s tail.

The nebula is part of a larger complex of gas and dust known as IC 5146. After the Cocoon, its most prominent feature is a dark nebula — a long ribbon of gas and dust. It absorbs the light of the stars behind it, so it looks black. It extends away from the Cocoon like a long tail.

Over the decades, astronomers have come up with many estimates for the distance to the complex — from about 1400 to more than three thousand light-years. And they’ve assumed that the Cocoon and the dark nebula were at the same distance.

But a study a couple of years ago came up with a new finding. Using a space telescope that produces highly accurate distance measurements, it put the dark nebula at about 1900 light-years, and the Cocoon about 700 light-years farther.

Regardless of the distance, both nebulas are giving birth to stars. In the dark cloud, the stars are born along thin filaments that are dozens of light-years long. Eventually, those stars will use up or blow away the dark dust around them, and their region will shine as brightly as the Cocoon Nebula.
 

Script by Damond Benningfield

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The blanket of air that surrounds Earth screens out some harmful forms of radiation, including ultraviolet and X-rays. That’s good for life, but bad for astronomy. It means that objects that produce those forms of energy are invisible. Yet those objects are some of the most energetic and interesting in the universe, so astronomers really want to see those wavelengths.

One solution is to send their telescopes into space. And one of the early ones was launched 50 years ago today. Named Copernicus, it was the last of four craft in the series of Orbiting Astronomical Observatories. The series was managed by Nancy Grace Roman, a NASA astronomer and the first woman to oversee a major spacecraft project. A new space telescope, scheduled for launch later this decade, is named in her honor.

Copernicus had two instruments. With them, the craft discovered the first “long-period” pulsars — the crushed cores of once mighty stars that spin once every few minutes. It kept an eye on many pulsars that spin in just a few seconds, as well as binary systems that emit a lot of X-rays. And it studied the hearts of galaxies that contain supermassive black holes encircled by disks of superhot gas.

Copernicus operated until February of 1981. Its findings greatly expanded our knowledge of the ultraviolet and X-ray universe — a universe that’s hidden from the surface by Earth’s comforting atmosphere.
 

Script by Damond Benningfield

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Many of the bright stars that decorate the night sky fit a similar profile. They’re roughly twice the size and mass of the Sun, a couple of dozen times its brightness, and only a fraction of its age. The list includes two of the stars of the Summer Triangle, which is high in the sky at nightfall, and the five middle stars of the Big Dipper, which is in the northwest.

Another star that fits the profile is in Lacerta, the lizard, which is half way up the northeastern sky. The faint little constellation’s brightest star is Alpha Lacertae. It’s about a hundred light-years away — far enough to dim some of its luster, so you need dark skies to see it.

Like the other stars that fit this profile, Alpha Lacertae is class “A.” That’s based on its surface temperature, which is thousands of degrees higher than the surface of the Sun. At that temperature, the star shines pure white.

Alpha Lacertae is about 400 million years old — just one-tenth the age of the Sun. It won’t live nearly as long as the Sun will, because it’s more than twice as massive as the Sun. Its gravity squeezes its core tightly, revving up its nuclear reactions. So Alpha Lacertae will live a “normal” lifetime of only a couple of billion years, versus about 10 billion years for the Sun.

After that, it’ll cast its outer layers into space, briefly surrounding its dead core with a bubble of gas — bringing its fairly short life to a colorful end.
 

Script by Damond Benningfield

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There are several ways to judge the brightness of a star. And a star that appears close to the Moon late tonight illustrates all three.

Aldebaran marks the orange eye of Taurus, the bull. It’s close to the lower right of the Moon at first light. A brighter orange light is farther to the upper right: the planet Mars.

The first way to judge Aldebaran’s brightness is apparent magnitude. That’s how bright it looks in our sky. On that scale, it’s at about point-eight-six — the 14th-brightest star system in the night sky.

The second way to judge its brightness is absolute magnitude. That scale compares how bright stars would appear if they were all lined up at the same distance from Earth: 32.6 light-years. That’s exactly half the distance to Aldebaran. So when you do the math, you get an absolute magnitude of minus-point-six-four. That means Aldebaran really is a bright star.

Stars produce a lot of light other than the form that’s visible to the human eye. The surface of Aldebaran is fairly cool, so it produces more infrared light than visible light. Combining all the wavelengths provides the star’s luminosity. On that scale, Aldebaran is about 440 times the brightness of the Sun. Still, it’s not nearly the brightest light out there. The most intense stars yet seen shine millions of times brighter than the Sun.

Even so, Aldebaran is probably in the top one percent on the list of bright stars.

Script by Damond Benningfield

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Even as several Mars missions continue to drive across the planet or probe it from orbit, another mission is signing off. Without a good sweeping by a dust devil, it’ll become a victim of dust — a fine orange powder that coats everything.

InSight arrived in November 2018. It’s not a rover, so it’s stayed in the same spot, in a plain called Elysium Planitia.

The craft has two major instruments. One is a seismometer. It’s recorded more than 1300 marsquakes. It heard the strongest on May 4th, at fifth magnitude. The quakes have helped scientists map the layers inside Mars. The crust is thinner than expected, while the core is bigger. The core is still molten, which means its iron must be mixed with other elements that melt at lower temperatures.

The other instrument was supposed to drill below the surface to measure the planet’s internal heat. It couldn’t penetrate the dirt, though, so it was abandoned.

InSight is powered by solar panels. Over the years, dust has collected on top of them. Engineers cleared some of it off, but not all. By May, the coating had reduced the craft’s power levels by 90 percent. So its instruments — including a weather station — are shutting down. Without a helping wind to clean it off, InSight should go silent later this year.

Look for Mars rising near the Moon after midnight. They’re high in the sky at first light. Mars looks like a bright orange star — colored by the dust that’s doomed Mars Insight.

Script by Damond Benningfield

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The Moon takes dead aim at one of the giants of the solar system tonight: Uranus, the seventh planet from the Sun. The planet will be close to the lower left of the Moon as they climb into good view, around midnight. The Moon will slide even closer to it as the night marches on.

As viewed from Hawaii and other parts of the central and northern Pacific, the Moon will actually cover the planet for a while — an event called an occultation. Uranus will disappear behind the bright limb of the Moon, then reappear on the dark edge.

Occultations require a precise alignment. Uranus lies close to the ecliptic, which is the Sun’s path across the sky. The Moon wanders back and forth across the ecliptic — sometimes to the north, some to the south. So most months, it’s too far from the ecliptic, so it gives Uranus a miss. Only when it’s at just the right location can it cover the planet.

That’s despite the fact that Uranus is big. It’s about four times the diameter of Earth — the third largest of the Sun’s major planets. But it’s also about 1.8 billion miles away, so it forms a tiny, faint disk in our sky — a big but tiny target for the Moon.

You need binoculars or a telescope to see Uranus. For most of the country, it’s a few degrees from the Moon as they rise, and a little closer at first light. It looks like a faint star with a hint of green.

Tomorrow: The Moon takes aim at a red planet.

Script by Damond Benningfield

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The middle of summer may not be the best time for a steaming pot of tea, but that’s just what the night sky offers. The brightest stars of Sagittarius, which is in the south at nightfall, form the outline of a teapot. And the hazy Milky Way seems to form puffs of steam from the spout.

The puffs are a combination of bright stars and gas, and dark clouds of dust in the disk of the Milky Way Galaxy. And if you look deeply into those puffs, you’ll see quite a few other little puffs of matter — star clusters and the vast clouds known as nebulae.

Two famous ones are directly above the spout, by about the width of your fist held at arm’s length — the Lagoon Nebula and the Trifid Nebula.

The Lagoon is a stellar nursery — a cloud of gas and dust that’s dozens of light-years across. It’s given birth to scores of stars, with more taking shape even now. Through binoculars or a small telescope, it looks like a hazy oval of light. Photographs reveal a reddish-pink glow, which is produced by hydrogen atoms being zapped by the radiation of young stars.

The Trifid is also a hot-pink stellar nursery, but with a different appearance. Dark lanes of dust across its center make it look like three different blobs. There’s also a nearby cloud of dust that reflects starlight, so it glows blue.

Look for these hotbeds of starbirth in the steam rising from the celestial teapot, low in the south on steamy summer nights.
 

Script by Damond Benningfield

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Astronomers have been looking for signals from other civilizations for more than 60 years. They haven’t found any — at least none they can confirm. But 45 years ago today, they heard one that generated a lot of excitement: the “wow” signal.

Astronomers at Ohio State were using a radio telescope to scan for evidence of extraterrestrial intelligence. And they found one signal that seemed to fit all the criteria. It was strong, it had a narrow bandwidth, and it was at the right frequency.

The signal lasted for 72 seconds — the longest the telescope could scan any specific object. So the signal probably was longer than that. It was recorded on a paper graph. And when the observatory director saw it, he wrote “Wow!” beside it.

But when the telescope looked for the signal again the next night, it got nothing. There was nothing on the following nights, either. And no one has heard a peep since then.

It’s not for a lack of trying. Many observatories scanned that region of space soon after the signal was reported. And they’ve kept looking since then. A big campaign a few years ago spent about a hundred hours looking for it. It’s challenging, though, because the precise location of the wow signal is uncertain.

The search area is in Sagittarius, which is low in the south at nightfall. Its brightest stars form the outline of a teapot. The search area is to the left of the teapot — the one location where we might have heard ET.
 

Script by Damond Benningfield

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Brilliant Jupiter — a planet that’s like the hub of a mini solar system — stays close to the Moon tonight. They climb into good view by about 11 p.m. and arc across the south later on.

Jupiter is far more massive than all the other planets in the solar system combined. In fact, it’s like the center of its own miniature solar system. It has about 80 known moons, a powerful magnetic field, and a big influence on the rest of the solar system.

Most of Jupiter’s moons are just big chips of rock. But several of the moons are fascinating worlds in their own right — like small planets. One is covered with volcanoes, while another has an ocean of liquid water beneath its icy crust.

Jupiter’s magnetic field is powerful — only the Sun’s is stronger. And its gravity is powerful as well. It helped push the planets into their current orbits, and helps keep them there. It sometimes pulls in asteroids or comets, or rips them apart if they get too close.

Jupiter is composed mainly of hydrogen and helium — the same elements as the Sun. And the proportions are about the same as well. That means Jupiter probably formed quickly, from the initial cloud of gas and dust that gave birth to the Sun.

Today, the planet emits more energy than it receives from the Sun — just like a star. And if it had grown to about 75 times its current mass, it would have ignited the fires of nuclear fusion and become a star — giving the Sun a sibling.
 

Script by Damond Benningfield

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