StarDate PodcastAuthor: McDonald Observatory
22 Jan 2017

StarDate Podcast

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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    More Fornax

    There’s no fountain of youth to make people look younger. But there is one for stars. It’s a process that sounds like a story from a 1950s B movie — “stealing” life from another star.

    A good example of a rejuvenated star is in the constellation Fornax, which is low in the south as night falls. It has only one modestly bright star, Alpha Fornacis, which is 46 light-years away.

    To the eye alone, it’s not much to look at. Binoculars, though, reveal that it consists of two stars. One of them is bigger and heavier than the Sun. It’s nearing the end of its life, even though it’s almost two billion years younger than the Sun.

    The other star of Alpha Fornacis is smaller than the Sun, and its surface is cooler than the Sun’s, so it glows orange. Yet it should be even redder than it is. And that’s where the story of rejuvenation comes in.

    The star has been identified as a blue straggler. That means its color shifted to slightly bluer wavelengths as the star aged. It might have done so by merging with another star, which would rev up its nuclear reactions, making it hotter and bluer. On the other hand, it might have changed color by simply stealing gas from a third star in the system.

    And there is some evidence of a third member of Alpha Fornacis — the corpse of a once-normal star. If it’s there, it may be about half as massive as the Sun, and quite close to the blue straggler — a dead star that gave part of its life to a stellar companion.


    Script by Damond Benningfield


  • Posted on 20 Jan 2017

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    Almost a century ago, astronomers partitioned the celestial sphere into 88 constellations. Most of them — the famous ones — date from ancient times. But 14 of them — none of which is famous — were created by a single man, in the 18th century.

    Nicolas Louis de la Caille was a French astronomer. In 1751, he set up an observatory at the Cape of Good Hope in South Africa to study the stars of the southern hemisphere. Over the following year, he cataloged about 10,000 stars. And later, he used those stars to draw new constellations in regions of the sky that weren’t visible from most of Europe.

    He called one of them Mons Mensa — table mountain. It honored a feature near la Caille’s observatory. He named all the others for tools that had scientific uses, such as the telescope and microscope, or artistic uses, such as the painter’s easel.

    One of those constellations is Fornax, the furnace, which is quite low in the south as night falls right now.

    It was originally called Fornax Chemica, after a small heater that was used for chemistry experiments. Another astronomer shortened the name a few decades later.

    Fornax isn’t much to look at — at least not with the eye alone. It contains only one modestly bright star, Alpha Fornacis, which we’ll talk about tomorrow. But a telescope reveals many treasures within its borders, including some beautiful individual galaxies, plus a giant cluster of galaxies — fiery visions in the celestial furnace.


    Script by Damond Benningfield

  • Posted on 19 Jan 2017

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    Fast Bursts

    When astronomers find a new type of object that goes “boom,” it takes a while to explain it. They have to figure out how far away the objects are, which reveals how bright they are. And they have to see them at different wavelengths to understand what they’re doing.

    They’re just starting that process for a class of objects known as fast radio bursts — blasts of radio waves that last no more than a few thousandths of a second. The first was discovered in 2007, and a few dozen others have been seen since then.

    Theorists have proposed several explanations for the bursts — from mergers between stellar corpses, to flares on the surfaces of highly magnetized corpses.

    The effort to understand them has been stymied because astronomers hadn’t seen any of the bursts at other wavelengths. But that changed with a burst that was discovered in November of 2013.

    A space telescope was looking at the same region of sky where the radio burst was discovered. An analysis, reported late last year, showed that the burst was accompanied by a blast of gamma rays, which are produced by some of the most violent events in the universe.

    That means that this particular burst took place far outside our home galaxy, so it had to be extremely energetic. That eliminates some possible explanations for the burst. But astronomers say that different bursts could have different causes. So it’ll take a while to fully understand the diverse nature of fast radio bursts.


    Script by Damond Benningfield


  • Posted on 18 Jan 2017

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    Super Supernovae II

    A supernova that was discovered a couple of years ago has astronomers doing a lot of head scratching. The explosion appears to be a couple of hundred times brighter than a typical supernova. But none of the models of how stars explode can fully explain why the blast was so bright.

    Supernova 15LH is thought to be the violent death of a massive star. Such a star dies when it can no longer produce energy in its core. The core collapses, and the surrounding layers are blasted into space.

    It’s not easy to explain a blast as powerful as 15LH, though — but that hasn’t stopped the theorists from trying.

    One team, for example, says that the energy could be coming from the interaction between the supernova blast wave and a shell of gas and dust around the star. The material would have been expelled from the star long before the explosion, and was moving away from the star.

    Other groups have come up with other ideas. One says that the supernova was powered by a magnetar — the star’s collapsed core. The super-dense, highly magnetized core would be spinning about a thousand times per second, pumping energy into the material around the core with each turn.

    And yet another idea says that 15LH wasn’t a supernova at all. Instead, it was the death throes of a star that was ripped apart by a supermassive black hole.

    With all these competing ideas, it’s likely to take a while to explain Supernova 15LH.

    We’ll talk about another stellar blast tomorrow.


    Script by Damond Benningfield

  • Posted on 17 Jan 2017

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    Super Supernovae

    Every supernova is a brilliant beacon — a stellar explosion that can outshine an entire galaxy. But in recent years, astronomers have logged a few dozen supernovae that take “brilliant” to extremes — they shine anywhere from about 10 to hundreds of times brighter than a typical supernova. And theorists are still trying to understand why.

    The first examples of “superluminous” supernovae were discovered more than a decade ago by Robert Quimby, a graduate student at the University of Texas at Austin. He was looking for supernovae across large patches of the sky when he discovered a couple of exceptionally bright examples. Since then, other astronomers have joined the search, leading to many new discoveries.

    These super-bright explosions appear to come in two varieties. One contains a lot of hydrogen — the element that makes up the bulk of most stars. The other type shows no hydrogen.

    The hydrogen-rich variety may involve a shell or bubble of hydrogen gas around the star that was expelled from the star before it exploded. If the bubble has expanded to just the right size, then the collision with the debris from the supernova could make it extremely hot. At such high temperatures, it would radiate enormous amounts of light — making it a superluminous supernova.

    The hydrogen-poor variety is a bit more mysterious. Theorists have proposed several explanations — from the magnetic cores of dead stars to stellar encounters with black holes. More about that tomorrow.


    Script by Damond Benningfield

  • Posted on 16 Jan 2017


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