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Record-busting supernova prompts new ideas on death of stars
Paris (AFP) Nov 14, 2007 Astronomers analysing the brightest supernova ever detected say the titanic flare has reshaped thinking about the death struggle of gigantic stars. Supernova SN2006gy, located 240 million light years away in galaxy NGC 1260, entered the record books in September last year when it dramatically brewed into an explosion 50 billion times brighter than the Sun. It was about 100 times brighter than the flash of a typical supernova, as a dying star is called. Poring over this extraordinary event, US stargazers said on Wednesday that the SN 2006gy was probably caused by a truly enormous star, a behemoth at least 100 times more massive than the Sun. And, they theorise, the star did not blow up just once -- but several times. "We usually think of a supernova as the death of a star, but in this case the same star can blow up half a dozen times," said Stan Woosley of the University of California at Santa Cruz, who led the study published in the journal Nature. Woosley's hypothetical model starts with what happens when an exceptionally big star -- something 90-130 solar masses -- nears the end of its life. The temperature in the stellar core gets so hot that some of the star's gamma radiation converts into electrons and their anti-matter counterparts, called positrons. The conversion causes the blast of radiation to suddenly fall, and the star begins to shrink. "As the core contracts it goes deeper into instability until it collapses and begins to burn fuel explosively," Woosley said. "The star then expands violently, but not enough to disrupt the whole star. For stars between 90 and 130 solar masses you get pulses. "It hits this instability, violently expands, then radiates and contracts until it gets hotter and hits the instability again. It keeps going until it loses enough mass to be stable again." Eventually, the star shrinks to about 40 solar masses, but even then the celestial fireworks aren't over, said Woosley. It contracts to an iron-rich core that collapses, ending with a searing gamma-ray burst Stars that are between 90 and 30 times the mass of the Sun are rare beasts, especially in our own galaxy, the Milky Way. But Woosley believes they may have been more common in the infancy of the Universe. A rival theory, meanwhile, is offered in Nature by Dutch astronomers Simon Portegies Zwart and Edward van den Heuvel of the University of Amsterdam. They suggest that SN 2006ga could not have been created from a single star, but from two very large stars that collided. Their calculations are based on what happens in a young, dense cluster of stars that are commonly seen at the centre of galaxies. Community Email This Article Comment On This Article Related Links Stellar Chemistry, The Universe And All Within It
Cosmological Data Affected By An Unexpected Source Of Radiation In Interstellar Space
Memphis TN (SPX) Nov 13, 2007The widely lauded discovery of small-scale structure in the cosmic microwave background may be seriously affected by a previously unidentified source of radio emission in our own Milky Way Galaxy. This is the conclusion arrived at by Dr. Gerrit Verschuur, Adjunct Professor of Physics at the University of Memphis. His work will be published in the December 10 issue of the Astrophysical Journal. |
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