StarDate PodcastAuthor: McDonald Observatory
30 Mar 2017

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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    Looking for Life

    The list of worlds in the solar system where life could exist keeps growing. Studies show that conditions could be right for microscopic life on Mars, some of the moons of Jupiter and Saturn, and even in the clouds of Venus. And in recent months, one more world has been added to the list: Pluto.

    When the New Horizons spacecraft flew past Pluto in 2015, it found evidence of an ocean beneath an ice-filled basin. The ocean could cover an area as big as Texas, and be up to 50 miles deep. And it could be heavy enough to act as a gravitational counterweight to the moon Charon, which always stays on the opposite side of Pluto.

    Recent studies suggest that the ocean could be kept liquid, slushy, or even syrupy by heat from radioactive elements deep inside Pluto, or by being mixed with ammonia.

    According to William McKinnon of Washington University in St. Louis, the ocean’s mixture of water, energy, and chemicals could be a good home for life. Not big life, like fish, or even relatively complex forms of microscopic life. Instead, it could be extremely simple organisms, much like the first life to appear on Earth.

    So far, of course, talk about life on Pluto or any other world is just that — talk. We haven’t seen life of any kind beyond Earth. Right now, we really don’t have the technology to probe for life on any world other than perhaps Mars. But we can keep speculating — identifying places to begin looking for life elsewhere in the universe.


    Script by Damond Benningfield

  • Posted on 28 Mar 2017

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    Growth Spurt

    One of the most impressive galaxies around climbs high across the south on spring nights. M87 is a giant elliptical galaxy, so it looks like a fuzzy rugby ball, with no spiral arms or other major features. It’s in the east at nightfall, and is visible through a small telescope.

    M87 contains several times as many stars as our home galaxy, the Milky Way. But like most other elliptical galaxies, it’s used up its supply of gas, so it doesn’t have the ingredients for making new stars.

    But a galaxy that’s like a younger version of M87 is making lots of new stars. It’s called COSMOS 11494. It’s about 11 billion light-years away, so we see it as it looked when the universe was just three billion years old.

    Despite its youth, the galaxy already has several times more stars than the Milky Way does today.

    And it gave birth to those stars in a hurry. Astronomers came to this conclusion after measuring two elements in the galaxy: magnesium and iron.

    Magnesium is cast into space when heavy but short-lived stars explode. In contrast, iron comes mostly from the explosions of longer-lived stars. The galaxy has the highest magnesium-to-iron ratio ever seen in a massive galaxy. That indicates the galaxy formed all of its stars in less than half a billion years.

    Alas, we can’t see the galaxy as it looks today. But if we could, it might resemble M87 — a giant galaxy that probably also gave birth to many stars in its youth.


    Script by Ken Croswell, Copyright 2016

  • Posted on 27 Mar 2017

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    M82 is one of the most vigorous galaxies around. It’s classified as a starburst galaxy. That means that, although it’s smaller than our galaxy, the Milky Way, it spawns far more stars. But new research suggests the star-making frenzy could soon come to an end.

    A galaxy makes new stars from clouds of gas, which permeate the space between stars. The densest clumps of this gas collapse, heat up, and begin to glow, shining as new stars. Each year, enough gas in M82 comes together to make the equivalent of 13 stars as massive as the Sun — a rate that’s about five times faster than the Milky Way.

    But M82’s star-making career can last only as long as its gas supply does. Each year, according to the new research, the galaxy adds just three and a half Sun’s worth of new gas from its surroundings. And each year, the galaxy’s own stars expel a lot more gas through stellar winds and supernova explosions.

    As a result, M82’s future looks bleak. When astronomers compare its gas consumption rate with its current supply of gas, they conclude that it’ll run out in just eight million years — the blink of a cosmic eye.

    Still, M82 could buy itself some time if additional gas falls onto it. So perhaps this amazing galaxy will keep on churning out bright new stars for a while longer.

    And M82 is in Ursa Major, the big bear. It stands to the upper left of the bowl of the Big Dipper as night falls right now, and is visible through a small telescope.


    Script by Ken Croswell, Copyright 2016


  • Posted on 26 Mar 2017

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    Cor Caroli

    When healthy twins are born, they usually have the same life expectancy. Barring accidents or disease, they should live about the same amount of time.

    When twin stars are born, though, it’s a different story. One of them is likely to expire long before its sibling. And it’s pretty easy for astronomers to tell which one will go first.

    Consider Cor Caroli, the brightest star of Canes Venatici, the hunting dogs. It’s in the east-northeast at nightfall. It’s the first meagerly bright star to the right of the tip of the Big Dipper’s handle.

    Cor Caroli consists of two stars, which probably were born together, from the same cloud of interstellar gas and dust.

    One of the stars is about three times the mass of the Sun, while the other is only half that heavy. And when it comes to a star’s life expectancy, it’s all about the mass. Heavier stars consume the nuclear fuel in the cores at a much faster rate than less-massive stars, so they expire much more quickly.

    The heavier star of Cor Caroli, for example, will live as a “normal” star for about 350 million years. After that, it’ll puff up to giant proportions, shining hundreds of times brighter than it is now. Then it’ll cast its outer layers into space, leaving only its hot but dead core.

    When that happens, its lighter twin will still be going strong. The more leisurely rate of nuclear reactions in its core means that it’ll shine for a couple of billion years after its flashier twin expires.


    Script by Damond Benningfield

  • Posted on 25 Mar 2017

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    Moving Day

    Venus is losing its identity. After tonight, it will no longer be the “evening star.” Instead, it’ll be the “morning star,” as it crosses the line between Earth and the Sun.

    This crossing is known as inferior conjunction, and it happens every 584 days — about 19 months. During that interval, the planet goes through a series of phases like the phases of the Moon.

    At conjunction, Venus is “new” — the entire hemisphere that faces Earth is in the planet’s own shadow, so we’re looking at its nightside.

    After conjunction, Venus becomes a thin crescent, which grows fatter as the weeks roll by. It’s during its crescent phase that Venus shines at its brightest. The planet is close to Earth then, so it forms a relatively large target in our sky. That proximity also means that more of the sunlight that Venus reflects into space reaches Earth. The combination makes the planet especially bright.

    After that, Venus gets “fuller,” as sunlight illuminates more of its Earth-facing side. But it also moves farther away, so it doesn’t look as bright.

    Venus is “full” at superior conjunction, when it lines up behind the Sun. After that, Venus begins to wane again as it once again prepares to cross between Earth and the Sun.

    Venus is probably too close to the Sun for most of us to see it this evening. But it could be visible in the east shortly before sunrise tomorrow — and will definitely be putting in a great showing within a few days — as the “morning star.”


    Script by Damond Benningfield

  • Posted on 24 Mar 2017


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