StarDate

The closest exoplanet is Proxima Centauri b — just four and a quarter light-years away. Its parent star, Proxima Centauri, is less than one percent as bright as the Sun. Every once in a while, though, it unleashes a huge outburst of energy and particles. And more than two years ago, astronomers saw the most powerful one yet.

Such “superflares” should happen several times a year. And that’s bad news for the planet. If it has an atmosphere, the flares could strip away any ozone atop it, bathing the planet in deadly ultraviolet light. They might even strip away the atmosphere itself.

The flare was observed with Evryscope — a set of a couple of dozen small telescopes in Chile. They’re combined into a single unit that looks like the top of a Star Wars droid.

The system takes a picture of the entire southern sky every two minutes. That allows it to monitor millions of stars. It looks for the stars to flare up. It also searches for exoplanets — looking for a star to grow a tad fainter as a planet passes in front of it.

Many of Evryscope’s target stars also are targets for TESS, NASA’s latest planet-hunting satellite. Astronomers compare results from them to see if a star with planets emits big flares — outbursts that could sterilize the planets.

Project scientists are installing a second cluster of telescopes in California. That’ll allow them to watch the entire night sky.

We’ll talk about another new telescope project tomorrow.

Script by Damond Benningfield

Our galaxy is a giant spiral. Most of its stars — including the Sun — reside in a thin disk that resembles a pancake. But the Milky Way isn’t entirely flat. Instead, a “bulge” of stars in the middle juts above and below the pancake.

A spiral galaxy in Draco, the dragon, is much flatter than ours. In fact, it has no central bulge at all. Instead, nearly all of its light comes from the disk.

NGC 5907 is about 55 million light-years away. Because it’s both flat and edge-on, astronomers get a good look at the faint structures above and below its disk. And they’ve detected faint trails in the galaxy’s halo — a vast region of space around the disk. The trails probably are streamers of stars from a nearby small galaxy. The galaxy shed the stars because the gravity of NGC 5907 is tearing it apart.

The same thing is happening in the Milky Way. In 1994, astronomers discovered a close galaxy in Sagittarius that our galaxy is tearing apart. The smaller galaxy’s stars are spilling into the Milky Way’s halo. That’s one reason that giant spiral galaxies grew so colossal: They stole the stars of lesser galaxies.

Draco is high in the north and northwest as night falls, above the Big Dipper. NGC 5907 is well above the end of the dipper’s handle.

Script by Ken Croswell

The Moon passes especially close to the bull’s bright orange “eye” tonight. Aldebaran is just an eyelash away from the Moon as they rise in late evening. Over the following hours, the Moon will pass even closer to the bright star, before they begin to pull apart.

Aldebaran looks so bright because it’s a giant star that’s close by. At visible wavelengths, it shines about 150 times brighter than the Sun.

But Aldebaran’s surface is thousands of degrees cooler than the Sun’s. Because of that, the star radiates much of its energy in the infrared — wavelengths that are too long for the eye to see. When you add that to the visible light, Aldebaran is more than 500 times the Sun’s brightness.

Although infrared energy has different wavelengths from visible light, it travels through space at the same speed: the speed of light. In fact, so do all forms of electromagnetic energy — from long radio waves to short gamma rays. So if astronomers look at a star with different kinds of telescopes at the same time, the telescopes all see the star as it looked at the same instant.

All of those wavelengths move at lightspeed — 670 million miles per hour. Yet even though Aldebaran is a close neighbor, it takes its light about 65 years to reach Earth. In other words, the star is 65 light-years away — a good example of just how vast the universe really is.

Script by Damond Benningfield

Sixty-five years ago, in a speech to the United Nations, President Dwight Eisenhower urged the world to abandon atomic weapons and use the atom for peaceful purposes.

The speech became known as “Atoms-for-Peace.” And it inspired astronomers to name a galaxy for it. So NGC 7252 became known as the Atoms for Peace galaxy. It was picked because it looks electrons orbiting the nucleus of an atom.

The galaxy got that shape because it’s the aftermath of a collision between at least two galaxies. The impact took place perhaps a billion years ago. It pulled out giant streamers of stars that span hundreds of thousands of light-years. And it stirred up clouds of gas and dust in the colliding galaxies, causing them to give birth to huge numbers of stars.

The core of one of the colliding galaxies survives in the center of NGC 7252. It forms a beautiful spiral that spans 10,000 light-years.

Eventually, the galaxy will settle down to form a smooth, featureless ball — and the Atoms for Peace outline will disappear.

NGC 7252 is in Aquarius. The constellation is low in the southeast at nightfall, and scooches across the south during the night.

Script by Damond Benningfield

Astronomers are developing bigger and bigger arrays of radio telescopes. By combining the signals from dozens or hundreds of antennas, they can produce extremely sharp images of the universe — far more detailed than possible with any single telescope.

That technique was pioneered by British astronomer Martin Ryle, who was born 100 years ago today.

After earning a degree in physics from Oxford, Ryle helped develop radar during World War II. After the war, there was lots of surplus military radar equipment. So Ryle put some of it to work to study the universe.

He first looked at the radio waves from the Sun and nearby stars. But it takes huge telescopes to produce detailed radio images. Ryle realized, though, that you could do the job by combining signals from two or more telescopes. The farther apart you placed the telescopes, the more detailed the observations.

Using this technique, Ryle and his colleagues compiled an extensive map of the radio sky.

Ryle and a colleague shared the 1974 Nobel Prize in physics — the first Nobel awarded specifically for astronomy.

Ryle thought radio astronomy should be limited, though. When astronomers used a giant radio dish to beam a message into space, he complained that it could lead to an alien invasion. He urged his colleagues to maintain radio silence — to use their telescopes to listen to the universe, not talk to it.

Script by Damond Benningfield

Dozens of galaxies orbit our own, but none compares to the Magellanic Clouds. These two galaxies are so bright and vibrant that they’re visible to the eye alone — but only from the southern hemisphere.

Hubble Space Telescope has tracked the motions of stars inside the smaller of the two galaxies. The observations suggest that it’s in serious trouble — the result of a recent collision with its brighter neighbor, the Large Magellanic Cloud.

The Small Magellanic Cloud is 200,000 light-years from Earth. The recent observations indicate that, unlike both the Milky Way and the Large Magellanic Cloud, the Small Cloud isn’t rotating. And stars on its outskirts are streaming away from its center, indicating that the outer regions of the galaxy are disintegrating.

The Hubble work also tracked the cloud’s path, and found the cause of its distress: it smashed right through the large cloud, which is about 10 times more massive. The collision occurred just 150 million years ago. The collision probably scrambled the stars so that they no longer orbit a common center. And it caused the galaxy to lose lots of gas.

As a result, its fate looks bleak. It probably will lose all of its gas, so it won’t be able to make more stars. This process will take a long time, though. So both of the Magellanic Clouds will shine brightly for a long time to come.

Script by Ken Croswell

The surface of every star “jiggles” like a bowl of Jell-O. By measuring those motions, astronomers can learn what’s happening far below a star’s surface. And thanks to a couple of space telescopes, they’ve studied thousands of stars — and even converted some of their jiggles to sound.

The technique is called asteroseismology. It measures tiny changes in a star’s brightness, as well as up and down motions on the surface. Those motions are caused by turbulence in the star’s outer layers. The turbulence creates waves that travel all around the star. They also travel deep into the star, then reflect back to the surface.

Measuring those waves can reveal the star’s interior structure and many other details.

Until recently, astronomers could measure the waves only with ground-based telescopes. But the blurring effect of Earth’s atmosphere makes it hard to see them, so there were good measurements for only a few stars.

But two space telescopes have expanded the technique to thousands of stars. CoRoT and Kepler have looked for planets by keeping a constant eye on hundreds of thousands of stars. Among other things, those observations have revealed the waves on the surfaces of many stars.

Astronomers have used those measurements to determine the ages of stars in a cluster, to find out where different groups of stars were born, and to discover magnetic fields in old stars — all from the “jiggles” on their surfaces.

Script by Damond Benningfield

Stars wander close to a black hole at their own peril. Any star that gets too close can be ripped apart by the black hole’s powerful gravity.

Astronomers reported a couple of these brilliant star deaths earlier this year. They monitored the events for about a decade, learning details about the black holes, and how they devour stars.

One of the events took place in the heart of a colliding galaxy that’s about 150 million light-years away. Astronomers first detected something odd happening there in 2005. They followed the event at all wavelengths, with telescopes on the ground and in space.

They determined that a star was being ripped apart by a black hole about 20 million times the mass of the Sun. Gas from the star formed a superhot disk around the black hole. As gas spiraled toward the black hole, magnetic fields funneled some of it into powerful jets. The jets raced into space at about a quarter of the speed of light.

The second event took place in a galaxy that’s about 800 million light-years away — not in its heart, but on its outskirts. X-ray telescopes in space detected a brilliant outburst. Over the following decade, the outburst faded and cooled. Astronomers concluded it was the result of a star being swallowed by a black hole about 50,000 times the mass of the Sun. The astronomers say it’s one of the best examples yet of an intermediate-mass black hole — a middle-range monster swallowing an unlucky star.

Script by Damond Benningfield

The most famous of all full Moons lights up the sky the next few nights: the Harvest Moon. It’s the full Moon closest to the autumnal equinox, which was yesterday.

The name originated several centuries ago, in northern Europe. The Moon’s light helped farmers harvest their crops long into the night — and not just because the full Moon is bright. At those latitudes, the full Moon rises only about a half-hour later each night at this time of year, so there’s not a long gap between sunset and moonrise. That made it possible to continue the harvest for several nights without a break before the Moon rose.

Technically, a full Moon lasts only an instant. It occurs when the Moon lines up exactly opposite the Sun in Earth’s sky. At that moment, sunlight illuminates the entire lunar hemisphere that faces Earth.

But the Moon orbits Earth at more than 2,000 miles an hour. So just moments before or after the instant of full Moon, the Moon is not quite opposite the Sun.

Practically, though, none of us can tell the difference. A day before or after the moment of full Moon, sunlight illuminates 98 percent or more of the lunar disk. So it looks full.

This year, the Moon will be full at 9:52 p.m. Central Daylight Time tomorrow night — the precise moment of the Harvest Moon. But it’ll look almost exactly the same on the nights before and after that. So the Harvest Moon spreads across three nights — a lot of light from the full or almost-full Moon.

Script by Damond Benningfield

Most of the stars in the Milky Way have companion stars. They travel through the galaxy together, bound by their mutual gravity. But many of those companions are quite remote — they can be separated by thousands of times the distance between Earth and the Sun.

The system with the widest separation yet seen is Fomalhaut. Its main star, now known as Fomalhaut A, is quite bright. Tonight, it rises to the lower right of the Moon, and is directly below the Moon around midnight.

For a long time, it looked like Fomalhaut was like the Sun — a single star. In recent years, though, astronomers have discovered that it has two companions. But they’re a long way from the bright star. In fact, the whole system spans more than three light-years.

Fomalhaut A is almost twice as big and heavy as the Sun, and about 17 times brighter.

Its closer companion is Fomalhaut B. It’s a little smaller and less massive than the Sun. It’s not visible to the eye alone, even though the system is just 25 light-years away.

The farther companion is Fomalhaut C. It’s so far from A that astronomers didn’t suspect that the two stars were related. But a study in 2013 showed that the stars are the same age, and they move through space in tandem. In other words, they’re companions.

Star C is a red dwarf — a bare cosmic ember. And it’s in the hinterlands of the Fomalhaut system — so far out that the star takes at least 20 million years to orbit its bright sibling.

Script by Damond Benningfield