StarDate PodcastAuthor: McDonald Observatory
24 Aug 2019

StarDate Podcast

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StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

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    Moon and Aldebaran

    The face of Taurus, the bull, is doomed. The V-shaped face is outlined by a star cluster known as the Hyades. But the cluster is falling apart.

    The Hyades is the closest major big cluster to the Sun — about 150 light-years away. All of its stars were born about 650 million years ago, from a giant cloud of gas and dust. Today, the stars all move through space together, as a single unit. But the cluster is less impressive today than it was in the past.

    A recent study looked at observations of stars in and around the Hyades by Gaia, a space telescope. It’s measuring the positions and motions of a billion stars. It revealed 500 members of the cluster itself. But it also revealed two “tails” of stars near the cluster — one ahead of it, and the other behind. Together, they contain more than 500 stars.

    The stars in these tails are about the same age as the stars of the Hyades. They also have the same chemistry, and they move with the same speed and in the same direction as the Hyades. That suggests the stars were members of the cluster in the past. They were kicked out by encounters with other stars, or by the gravitational pull of the rest of the galaxy.

    So someday, the entire cluster may be pulled apart — destroying the face of the bull.

    Look for the face at dawn tomorrow to the right of the Moon. The bright star close to the Moon is Aldebaran, the bull’s eye. Although it’s at one point of the V, it doesn’t belong to the cluster — it’s on its own.

    Script by Damond Benningfield

  • Posted on 23 Aug 2019

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    Dark Mergers

    Mergers between big galaxies are violent events. They can kick millions or billions of stars into intergalactic space, and dramatically alter the orbits of other stars. They can trigger the birth of millions of new stars — many of which will quickly blast themselves to bits. And they can result in the merger of two supermassive black holes — creating one of the brightest objects in the universe.

    Most big galaxies have giant black holes in their cores. The one at the heart of the Milky Way, for example, is about four million times the mass of the Sun. And the black holes in other galaxies can be billions of times the Sun’s mass.

    When two galaxies with such giant black holes come together, the black holes fall toward each other. They can stage a cosmic “dance” that lasts for hundreds of millions of years. As they loop around each other, they emit gravitational waves, causing them to move closer together.

    As the black holes spiral closer, they stir up giant clouds of gas and dust. Some of this material is funneled toward the black holes. As it moves closer, it’s heated to millions of degrees. That creates a quasar — one of the more brilliant objects in all the universe.

    The fireworks might not end when the black holes finally merge. Instead, the combined black hole might be kicked out of the merging galaxies. It can drag stars and gas clouds along with it — creating one final round of pyrotechnics as it heads for intergalactic space.

    Script by Damond Benningfield

  • Posted on 22 Aug 2019

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    Galactic Collision

    The Milky Way is headed toward a galactic pile-up. Our home galaxy is likely to merge with M31, our closest big neighbor galaxy. That will trigger the birth of millions of new stars. And it will fling the Sun and its planets into a new orbit — and perhaps out of the galaxy entirely. There’s no need to worry about it, though. It won’t start for another four and a half billion years.

    M31 — also known as the Andromeda Galaxy — is about two and a half million light-years away. But it’s moving toward us. Every hour, it covers about a quarter of a million miles — roughly the distance between Earth and the Moon.

    The Gaia satellite measured the precise motions of more than a thousand stars in M31. A team of astronomers used those measurements to come up with a better timeline of the encounter.

    The team calculated that M31 will pass about 400,000 light-years from the Milky Way in four and a half billion years. The haloes of “dark matter” that envelop the galaxies will create friction. That’ll slow the galaxies down and pull them together.

    They’ll pass through each other a few times. Each encounter will fling huge ribbons of stars out of each galaxy. There’s a chance the Sun could get caught in such a ribbon, carrying Earth along with it. The merger also will trigger intense bouts of starbirth — creating millions of new stars.

    Eventually, Andromeda and the Milky Way will merge, creating a single monster galaxy — the final result of a galactic pile-up.

    Script by Damond Benningfield

  • Posted on 21 Aug 2019

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    Merging Galaxies

    NGC 6052 is a mess. It looks a little like a pair of big spiders locked in mortal combat. Instead, though, it’s two galaxies that are staging their own combat — they’re in the process of merging.

    The galaxies are about 230 million light-years away. They’re in the constellation Hercules, which is high in the western sky on August evenings. Both galaxies are spirals — cosmic pinwheels that are similar to our own galaxy, the Milky Way.

    As the galaxies of NGC 6052 come together, gravity is throwing some of their stars out of the galaxies in giant ribbons. At the same time, clouds of gas and dust are slamming together to give birth to new stars. In fact, colliding galaxies create new stars at an amazing rate — hundreds of times more stars than the Milky Way is making.

    Collisions between galaxies are common. So most of the galaxies in the present-day universe probably are the result of a series of mergers between smaller galaxies.

    In fact, a study a couple of years ago found that we should be able to see up to two trillion galaxies. But many of those galaxies are puffballs that existed when the universe was young, and their light is just now reaching us. If we could take a snapshot of the universe right now, we’d see only a couple of hundred billion galaxies. Most of the early galaxies would have vanished — swallowed up in galactic mergers.

    The Milky Way is headed toward its own big merger, and we’ll talk about that tomorrow.

    Script by Damond Benningfield

  • Posted on 20 Aug 2019

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    We have lots of addresses. After your street address, city, state, and country, you might add lines for Planet Earth, the solar system, and the Milky Way Galaxy.

    The Milky Way is just one of 200 billion galaxies or more in the present-day cosmos. Each one is an “island universe” — a vast collection of stars, gas and dust for making new stars, and mysterious “dark matter.”

    Galaxies come in a few basic layouts. Many of them are wide, thin disks like the Milky Way. Waves traveling through the disks form beautiful spiral arms, so the galaxies look like pinwheels.

    Others are shaped like fuzzy rugby balls. Their stars are old, and the galaxies don’t have much gas for making more stars. And still others are blobs with no easily definable shape.

    There’s huge variety within these groups. Some galaxies are little more than puffballs. They’re only a few dozen to a few hundred light-years wide, and they contain only a few hundred million stars — a tiny fraction of the size and population of the Milky Way.

    At the opposite end of the scale are the largest galaxies. They span a million light-years or more, and they host a hundred trillion stars — numbers that dwarf the Milky Way.

    With so many galaxies around, it’s inevitable that they occasionally sideswipe each other, or even ram together head-on. In the end, the galaxies may merge, forming even bigger “island universes.”

    We’ll talk about about one example of merging galaxies tomorrow.

    Script by Damond Benningfield

  • Posted on 19 Aug 2019


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