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NMSU professor co-authors astronomical paper on Bolshoi supercomputer simulations

Supercomputers have been used for years to create simulations scientists use to answer questions about the universe, from the time of the Big Bang to the present. Now, a New Mexico State University astronomy professor, together with a large group of colleagues, has released the most accurate set of "Bolshoi" supercomputer simulations to date. These simulations are anticipated to become the new benchmark standard in high-quality theoretical modeling of the universe.

"This has been a significant collaboration many years in the making between NMSU, the University of California at Santa Cruz, and also researchers around the world," Anatoly Klypin said. "Now we can create even higher quality simulations of the formation of galaxies. We can also use this information to teach students of astronomy about the universe and train them on the use of supercomputers."

"Bolshoi" is the Russian word for "great" or "grand."

Large cosmological simulations run on supercomputers are now the basis for much current research on the large-scale structure of the universe and the evolution of galaxies. Due to significant advances in both the power and speed of supercomputers and the sophistication of computer codes over the past half-decade, "the Bolshoi simulation is better in every respect" than any previous simulation, said Joel Primack, director of the University of California High-Performance AstroComputing Center (UC-HiPACC).

Klypin wrote the computer code for the Bolshoi simulation, which took six million CPU hours to run on the Pleiades supercomputer - recently ranked as seventh fastest of the world's top 500 supercomputers - at NASA's Ames Research Center.

The Bolshoi simulation is based on data from a highly successful NASA Explorer mission, the Wilkinson Microwave Anisotropy Probe, that measured the detailed structure of the cosmic microwave background radiation - radiation left over from the Big Bang that formed the universe 13.7 billion years ago - observed and catalogued by the WMAP science team in 2008. That team produced high-resolution maps of the entire sky, plotting the anisotropy, or unevenness, of the temperature and other characteristics of the cosmic microwave background radiation in great detail and revealing a wealth of information about the history, structure and composition of the early universe.

In addition, the Bolshoi simulation is based on Lambda Cold Dark Matter cosmogony, now accepted as the standard modern theoretical framework for understanding the formation of the large-scale structure of the universe. It is now known that ordinary matter makes up less than 5 percent of the universe. About five times that much - about 23 percent - of the density of the universe is made of invisible "cold dark matter," whose existence is detected through its gravitational influence. The remaining 72 percent of the cosmic density is dark energy. Every galaxy, including our own Milky Way, resides at the center of a giant halo of dark matter roughly ten times larger in radius and mass. The ΛCDM cosmogony makes detailed predictions about the emergence of structure in the universe hierarchically through gravitation. Specifically, it predicts that repeated mergers of smaller things ultimately end up creating bigger things.

Thus, the Bolshoi simulation models not only how the visible universe of stars, gas and dust evolved, but also how the much more vast invisible universe evolved. One principal purpose of the Bolshoi simulation is to compute and model the evolution of dark matter halos - thereby rendering the invisible visible for astronomers to study and to predict structures that they could then seek to observe.

A lower-resolution simulation called BigBolshoi or MultiDark, a collaboration with Spanish and German theoreticians, was run on Pleiades to predict the properties and distribution of galaxy clusters and other very large structures in the universe in a volume four billion light years across, thus 64 times larger. A higher-resolution miniBolshoi simulation of a smaller region is currently being run on Pleiades, to model the formation and distribution of the tiniest galaxies. Results from all Bolshoi variants are being made publicly available via the MultiDark Database, hosted by the Leibniz-Institute for Astrophysics Potsdam in Germany and supported by grants from Spain and Germany.

The simulation research was funded by grants from NASA and the National Science Foundation.

For more information, go to http://hipacc.ucsc.edu/Bolshoi/.