Scientists have generated the largest and most realistic cosmological simulations of the evolving universe to-date, thanks to NASA's powerful Pleiades supercomputer. Using the "Bolshoi" simulation code, researchers hope to explain how galaxies and other very large structures in the universe changed since the Big Bang.

To complete the enormous Bolshoi simulation, which traces how largest galaxies and galaxy structures in the universe were formed billions of years ago, astrophysicists at New Mexico State University Las Cruces, New Mexico and the University of California High-Performance Astrocomputing Center (UC-HIPACC), Santa Cruz, Calif. ran their code on Pleiades for 18 days, consumed millions of hours of computer time, and generating enormous amounts of data. Pleiades is the seventh most powerful supercomputer in the world.

"NASA installs systems like Pleiades, that are able to run single jobs that span tens of thousands of processors, to facilitate scientific discovery," said William Thigpen, systems and engineering branch chief in the NASA Advanced Supercomputing (NAS) Division at NASA's Ames Research Center.

"The Bolshoi simulation is an excellent example of work done in support of NASA's science goal to understand how stars, galaxies and planets are formed, in order to get a picture of how the universe has changed over billions of years," Thigpen added.

The Bolshoi simulation models the distribution of dark matter across a span of one billion light years to better understand how structures like galaxies formed in the early universe. Dark matter - a mysterious substance with immense gravity that does not interact with normal matter and cannot be directly observed - makes up roughly 25 percent of the universe.

Bolshoi uses data gathered from NASA's highly successful Wilkinson Microwave Anisotropy Probe (WMAP) mission. MAP measured the faint "cosmic microwave background" left over from the Big Bang - the signature of early matter in the universe - to trace the eventual formation of large structures.

The universe is approximately 13.7 billion years old. Pleiades' new graphics processing units from NVIDIA, Corp. have greatly sped up parts of the Bolshoi calculations.

"Being able to tap into the power and speed of Pleiades has improved the Bolshoi simulation in every respect," said Joel Primack, director of the University of California High-Performance AstroComputing Center (UC-HIPACC) and co-investigator on two studies reporting on the simulation results, slated for publication in the Astrophysics Journal in October.

"In addition, ultra-high-resolution images and animations created by NAS visualization experts have provided the basis for imaging and interpreting our latest simulation results," Primack said.

NAS has produced breathtaking images and animations that show the formation, evolution, and merger of "dark matter halos," the massive gravity wells in which galaxies form. These visualizations were made possible by custom software tools developed by the NAS data analysis and visualization team.