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NEW MODEL EXPLAINS SOUND BEFORE SIGHT
Or to put it another way, says Burrows, "it's the sound waves that actually cause the star to explode." This conclusion sounds paradoxical, says Burrows. But if borne out, it would solve a long-standing puzzle. Astronomers know that a supernova explosion can occur only in a very massive star--say, 10 to 25 times the mass of our own Sun. And they know the initial release of energy is confined to the very deepest core of the star. The puzzle is how the energy gets out. Previous simulations suggested the layers of gas surrounding the core were just too dense for the energy to escape. The simulated blast wave would stall and die before it reached the star's surface, as if it were muffled by a blanket, and observers on the outside would see nothing at all. But, those earlier simulations had always used highly simplified models of supernovae outbursts, because that was the only way to cope with the complex calculations. Many, for example, assumed the explosions were completely spherical and symmetric. Now, however, Burrows and his colleagues have developed computer models that allow them to simulate a more natural flow of material and radiation, especially in the central regions of the star. They found that the initial energy release at the core pulsates the surrounding layers of gas, with a typical frequency around middle C. Within a fraction of a second, moreover, the pulsations grow so violent they tear the star apart, blowing its outer layers into space. Burrows has posted images and videos of the simulations online. He and his colleagues were funded by the National Science Foundation, the Department of Energy, and the Joint Institute for Nuclear Astrophysics. They will be publishing their research in the Astrophysical Journal.
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