StarDate

In the past decade, astronomers have “heard” almost 400 mergers between black holes. The signals were carried by gravitational waves – tiny ripples in spacetime. They’ve revealed that some of the black holes probably had undergone earlier mergers – making them third-generation black holes.

Gravitational waves are produced by the motions of any object. But the waves are extremely weak. So far, the only ones that have been detected were produced by mergers involving black holes or neutron stars – dense, heavy objects that come together in a fraction of a second.

The characteristics of the waves reveal the masses of the merging objects. They also reveal how the objects were spinning, and how they were orbiting before the merger. And those details provide hints to the existence of third-generation black holes.

One example was discovered in late 2024. A black hole about 20 times the mass of the Sun merged with one about six times the Sun’s mass. Scientists determined that the heavier black hole probably formed from an earlier merger. They even calculated the details of those black holes: about 7 and 13 times the mass of the Sun.

Third-generation black holes probably form in places where lots of black holes are jammed close together, such as the hearts of star clusters. That keeps a merged black hole from escaping – setting up the possibility of more mergers ahead.

Script by Damond Benningfield

The Moon charges at the Pleiades late tonight. As seen from most of the United States, it will pass especially close to the star cluster – either just skimming its edge or briefly covering some of its stars.

The cluster is home to more than a thousand stars of all varieties. The ones that are visible to the eye alone are especially big, hot, and bright. But they’re greatly outnumbered by stars that are much smaller, cooler, and fainter. Many of the stars belong to systems of two stars or more. And the cluster also hosts many “brown dwarfs” – objects that are more massive than planets, but not heavy enough to shine as true stars.

Over the decades, there’s been a lively debate about the distance to the cluster. Different telescopes and techniques have provided measurements that vary by many light-years. The best current number puts the distance at about 440 light-years.

But that’s the distance to the center of the Pleiades. The cluster actually spans several dozen light-years in all directions. So as you look at the cluster, the light you see from the stars that are closest to Earth headed our way dozens of years earlier than the light from the stars that are farthest – an out-of-sync view of a well-known star cluster.

The cluster’s brightest stars form a tiny dipper shape, although it’ll be tough to make out through the moonlight. The cluster will be especially close to the Moon at dawn.

Script by Damond Benningfield

The center of the Milky Way Galaxy is packed with treasures: stars, dead stars, gas clouds, and lots of planets. And a new space telescope will spend a lot of its time sorting it all out.

That’s one of several big projects for Nancy Grace Roman Space Telescope, NASA’s next big space observatory. The telescope will see the heavens as clearly as Hubble Space Telescope does. But its view will be much wider. And it’ll study the universe mainly in the infrared – wavelengths that are invisible to the human eye.

Roman will tackle some of the biggest problems in modern science. As one example, it’ll look away from the center of the Milky Way to study more than a billion other galaxies, and to look for exploding stars. That combination will help us understand how the universe is expanding – a key for deciphering the mystery of dark energy.

The telescope’s survey of the center of the galaxy could reveal thousands of new planets. And a special instrument – using a technique proposed by Nancy Roman herself – could provide images of some of those planets. A planet will appear only as a bright dot, with no detail. But breaking down its light will tell us a bit about the planet’s size, temperature, and composition.

The center of the Milky Way is in Sagittarius, which is low in the south at nightfall. Its brightest stars outline a teapot. The heart of the galaxy is in the steam above the spout of the teapot.

Script by Damond Benningfield

The planet Venus and the star Spica huddle close the next few evenings. They’re quite low in the west-southwest in early twilight. Venus is the brilliant “evening star.” Tonight, Spica stands close above it. Venus will slide to the left of Spica over the following nights.

Venus is named for the Roman goddess of love and beauty. It’s the only major planet in the solar system named for a female character. With a few exceptions, all of the features on its surface are named for women as well – from both mythology and real life.

No features were named until the Space Age. Venus is covered by an unbroken blanket of clouds, so we can’t see the surface. Radio telescopes on Earth peered through the clouds in the ’60s, and discovered the first known features. All the other features were mapped by spacecraft in orbit around Venus, which scanned the planet with radar.

Today, more than 2,000 features have been named – mountains, craters, canyons, plains, and others. Their names have come from cultures around the world and across the ages.

One volcano is named Anuket, for an Egyptian river goddess, while another is named La Shen for a Chinese goddess. Other features are named for Anne Frank, Jane Austen, Pocahontas, and Queen Isabella of Spain, along with other writers, artists, rulers, scientists, and women from many other fields – all commemorated on the planet Venus.

Script by Damond Benningfield

If you look carefully at pictures of Saturn, you’ll probably notice something odd about the planet – it looks mashed down, like a beachball that a child is sitting on. The planet is more than 7,000 miles wider through the equator than the poles – only a bit less than the total diameter of Earth. That makes it the “flattest” planet in the solar system.

Saturn is the Sun’s second-largest planet, after Jupiter – more than nine times the size of Earth. But it’s much less dense than any other planet. It’s a big ball of hydrogen and helium – the two lightest elements – wrapped around a messy core of rock and metal.

Despite its size, Saturn spins in a hurry – its day is less than half as long as a day on Earth. That high-speed rotation pushes material outward at the equator – giving Saturn that “squashed” appearance.

That shape affects the planet’s gravity. Saturn’s poles are much closer to the center of the planet than the equator is. And anything at the equator is being pushed outward by the high-speed rotation. The combination means that you’d weigh about a third more at the poles than at the equator – perhaps making you feel more squashed on this giant but squashed planet.

Look for Saturn close to the lower right of the Moon as they climb into good view, in mid-evening. It looks like a bright golden star.

Tomorrow: famous women on the planet Venus.

Script by Damond Benningfield