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Star self-destructs before astronomers' eyes
21 May 2008
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Hazel Muir



Astronomers happened to be looking at the moment a star exploded (Image: NASA/Princeton U/Gemini Observatories)
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Alicia Soderberg, Princeton University
Swift X-ray Telescope
Energetic X-ray Imaging Survey Telescope


Talk about right place, right time. Quite by chance, astronomers have captured footage of a star blowing itself to smithereens.
Stars heavier than about eight times the mass of the sun meet their deaths in catastrophic explosions when their core runs out of fuel. The core can collapse into a black hole or neutron star, generating a shock wave that ploughs outwards, blasting the star's atmosphere apart.
Hundreds of supernovae are seen every year, but usually days or weeks after the event (in the Earth's time frame), when the optical glow of radioactive nickel in the debris reaches a peak. By then it is often too late to determine what kind of star exploded or what events led up to the blast.
Alicia Soderberg from Princeton University and her colleagues were using an X-ray detector on NASA's Swift space telescope to observe a galaxy 88 million light years away when they saw a brief but intense X-ray signal. This is characteristic of a supernova explosion, and is emitted by hot gas trapped just behind the shock wave as it bursts out of a star. "It only lasted a few minutes and then the whole show was over," says Soderberg.
The observations suggest the star that exploded was of a hot, massive and luminous variety called a Wolf-Rayet star, and that the shock wave took about 10 minutes to travel from the stellar core out to the surface.
Astronomers may not need to be so fortunate in future. Though current satellite-borne X-ray telescopes do not scan enough of the sky with sufficient regularity to have a good chance of catching signals from exploding stars, proposed satellites such as NASA's Energetic X-ray Imaging Survey Telescope (EXIST), which will image the entire sky every 95 minutes, could pick up hundreds of these blasts every year.