The most detailed computer simulation yet of the turbulent motion inside an exploding star has been carried out by the world's foremost supercomputer.
The results help explain how nuclear reactions in a star's core suddenly speed up to produce some of the most powerful explosions in the universe – Type Ia supernovae.
The simulation was carried out by William Cabot and Andrew Cook, both at Lawrence Livermore National Laboratory in California, US. They ran it on the world's fastest supercomputer, IBM's BlueGene/L, which is located at the same laboratory. This computer can perform a staggering 281 trillion mathematical operations each second. Watch a 5.1 MB QuickTime movie of the simulation.
The brightness of Type Ia supernovae is predictable, allowing astronomers to gauge distances to other galaxies by measuring their glow. Such measurements have been crucial to the discovery of dark energy, thought to be accelerating the expansion of the universe.
But there are slight, unexplained variations in Type Ia brightness, and this adds uncertainty to distance measurements. A better understanding of the processes that drive these explosions could therefore help refine distance calculations and shed more light on dark energy.
Type Ia supernovae occur when a white dwarf star grows so massive that pressure in its interior triggers a reaction that forms an expanding wave inside the star as carbon and oxygen are transformed into heavier elements.
The wave moves slowly at first, and details of how it accelerates have long been mysterious. Without this sudden acceleration, the star would be like a broken firecracker, says Alan Calder of The University of Chicago, in Illinois, US. "You get a burn, but not the fast pop," he says.
Scientists have long suspected that the churning of raw material inside a star can help accelerate the wave, by bringing fresh fuel to the reaction. The new simulation hints that this effect may be more important than previously supposed. It reveals that churning mixes up material more rapidly than lower resolution simulations had suggested.
"This effect could be quite important," says Michael Zingale of Stonybrook University, in New York, US, who also works on supernova simulations.
While the new simulations shed some light on a highly complex phenomenon, Calder notes that the general theory behind supernovae themselves "still needs work".
Journal reference: Nature Physics (DOI: 10.1038/nphys361)
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18:53 05 September 2008
