Astronomers track stars' bizarre behavior

    After millions of years of pulsating, a white dwarf in the constellation Hercules stopped one day and took a month off.

    For the next few weeks, telescopes around the globe will be aimed at the same dying star. Astronomers hope it can help them unlock the mysterious behavior of the stars known as white dwarfs. WHYY’s health and science reporter Kerry Grens has more.


    Even the pea-green chairs at the Mount Cuba Observatory in Greenville, Delaware hark back to 1967, when it was built. Astronomers have to crank open by hand the dome over the telescope and an old motor rotates the dome to line the slit up with the right part of the sky. In coming weeks, when night falls, observers at Mount Cuba will aim the telescope at one of three white dwarfs in our galaxy. Judi Provencal is a professor at the University of Delaware and the director of a 23-year-old project called the Whole Earth Telescope. It’s a collection of 22 observatories around the world, all watching the same select stars.

    Provencal: This particular star is in the constellation Hercules.

    Provencal points to a computer screen, at a fairly unremarkable white dot against a night sky: the star called GD358.

    Provencal: The idea was to be able to observe a star continuously for 24 hours a day for period of a couple weeks because you can’t do that from a site like this. Like right now we can’t observe because the sun is out.

    The team will zero in on one white dwarf, with the unfortunate name of WDJ1524-0030. If skies are clear extra telescopes will monitor the other targets, including GD358. The reason for continuous monitoring, rather than just a snapshot, is that some stars actually do things. They pulsate.

    Provencal: These white dwarf stars are the mass of the sun, roughly, compressed down to something the size of the earth…It takes too much energy for them to expand outward and in, so what they do is they slosh, side to side, like an ocean wave, propagating around the surface.

    White dwarfs are considered dying stars, and they will continue to pulsate for millions of years. Unless it’s the star GD358.

    Provencal: Back in 1996 it did something weird.

    After presumably eons of pulsating, the star’s pattern changed one day.

    Provencal: And then it stopped pulsing pretty much for about a month.

    It just went quiet. Inexplicably. Then, it just started pulsating again.

    Provencal: So I’ve been trying to track down, to watch it and see if it does it again, but it hasn’t so far.

    Steven Kawaler is a professor at Iowa State University.

    Kawaler: That fits her style. She’s always interested in the ones that behave in ways that theorists can’t understand at all.

    Kawaler is one of those theorists in this field called astroseismology.

    Kawaler: You can look at stars with excruciating detail, and start seeing that two stars that otherwise look just the same differ and then try to figure out why. And that clearly is going to teach us a lot about the details of how stars are put together.

    When GD358 went back to pulsating, it didn’t quite return to normal. Its pattern was shifted. This year, another star did the same thing.

    Judi: The WDJ1524 target was pulsating with frequencies very similar to this star last year. When we looked at it at the beginning of May it had put all its power into a much shorter period frequency. And we don’t really understand why.

    For the next three weeks, Provencal is keeping watch on WDJ1524 as data come in from telescopes around the world. Perhaps this star can lend her clues about GD358’s erratic outburst.

    Provencal: We’ve tossed around the idea of maybe a comet hit it, or an asteroid or something like that.

    Or maybe a magnetic field interfered with the pulsations. Whatever the reason, it unsettles theories of how white dwarfs behave. And predictions of our own sun’s fate. Right now, astronomers think it’s on track to become a white dwarf … in about four billion years.



    Past and future of the Whole Earth Telescope

    Steven Kawaler, professor at Iowa State University, explains why the discovery of a planet around a white dwarf shows promise for our own planet’s fate. Listen:


    Ed Nather, founder of the Whole Earth Telescope, describes one of the earliest accomplishments he made with co-founder Don Winget. Listen:


    Steven Kawaler explains that the next frontier for the Whole Earth Telescope is to use white dwarfs to study a basic process happening all the time in our own sun. Listen:


    Telescopes in space: Kerry Grens talks with Steven Kawaler about the role of NASA’s new Kepler mission in astroseismology. Listen:



    Judi Provencal cranks the dome open by hand. The Mount Cuba Observatory was built in 1962. Click to play.


    More on astronomy from Skytalk


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