Tuesday, November 21, 2006

"Supercomputer study shows Milky Way's [posited] halo of dark matter"

Supercomputer study shows Milky Way's halo of dark matter in unprecedented | SpaceRef
"Initially, gravity acted on slight density fluctuations present shortly after the Big Bang to pull together the first clumps of dark matter. These grew into larger and larger clumps through the hierarchical merging of smaller progenitors. This is the process the UCSC researchers simulated on the Columbia supercomputer at the NASA Ames Research Center, one of the fastest computers in the world. The simulation took a couple of months to complete, running on 300 to 400 processors at a time for 320,000 'cpu-hours,' Diemand said.
Coauthor Michael Kuhlen, who began working on the project as a graduate student at UCSC and is now at the Institute for Advanced Study in Princeton, said the researchers set the initial conditions based on the most recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) experiment. Released in March, the new WMAP results provide the most detailed picture ever of the infant universe.
The simulation starts at about 50 million years after the Big Bang and calculates the interactions of 234 million particles of dark matter over 13.7 billion years of cosmological time to produce a halo on the same scale as the Milky Way's. The clumps within the halo are the remnants of mergers in which the cores of smaller halos survived as gravitationally bound subhalos orbiting within the larger host system. "