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The Sciences

#95: Computer Builds 
A Perfect Galaxy


Nature did it in 13 billion years. Computer does it in 9 months.

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It took nature 13 billion years to create our galaxy, the Milky Way. Last August a group of scientists reported that they had replicated the feat in just nine months. To be fair, they created only a digital simulation, nicknamed Eris, but it is the first one to accurately reproduce the details of a galaxy like our own.

Previous simulation attempts often produced a galaxy with an oversize bulge and too small a surrounding disk. The difference with Eris, says astrophysicist Piero Madau of the University of California, Santa Cruz, is realistic star formation: His team included equations that precisely modeled how exploding stars expel gas from the central regions and spark the birth of new stars in clusters throughout the galaxy.

The findings boost the leading theory of galaxy formation, called Lambda–Cold Dark Matter, which proposes that slow-moving clumps of invisible dark matter gravitationally capture visible matter and help shape it into galaxies. Observations support the theory, but some physicists had been concerned that computer simulations of it kept coming out wrong. Says Madau: “There is no need, as some had argued before, to abandon the theory.”


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