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Feature - Cosmic simulation

Feature - Cosmic simulation

This video simulates Governato's new model of the formation of a dwarf galaxy over time. It is the first such simulation to match observations in terms of the mass of stars and dark matter in the galactic core. Video courtesy of Fabio Governato.

Cosmic structure formation theory has passed test after test, predicting how many galaxies will form, where they will form, and what type of galaxy they will be. But for almost 20 years, its predictions about the central mass of dwarf galaxies have been wrong.

"Potentially, this is a very big problem for the model," said Fabio Governato, a researcher at the University of Washington in Seattle. "It might imply that the dark matter particle that we think is the correct one is not the correct one, or maybe that gravity works differently than we think it does. So this is a very fundamental problem for physics."

Now, a simulation running on computer resources at NASA Advanced Supercomputing Division, the Arctic Region Supercomputing Center, and TeraGrid may have resolved this conundrum. Their secret? A more realistic model of how stars form and die, incorporated into the existing cosmic structure formation theory.

It turns out that when a star near the galactic center explodes, a lot of interstellar gas is blown away from the center of the galaxy. "As a result, less stars form at the center, because there is less gas," Governato explained.

"It kind of came as a surprise," he added. They knew that when stars explode they can eject gas. "It just was not clear to us how much it would impact galaxy formation."

To create the simulation, Governato worked with Thomas Quinn, also from the University of Washington, and James Wadsley from McMaster University. They used about a million computer hours, which means that it would have taken close to a hundred years to run the same simulation on the average desktop, according to Governato.

"[The model is] more impressive. It's more realistic," said Anatoly Klypin, a researcher based at New Mexico University who is also working on cosmic structure formation theory. "But it still requires a lot of improvement and understanding of how stars are forming in the universe."

The creation of this kind of model is a long process. Worldwide, there are many teams working on their own versions; each attacks the problem from a different angle. Klypin's team is exploring the large-scale effects of energy released by young stars.

"Stars are forming, and young stars release large amounts of energy into the gas that surrounds them," Klypin explained. "That energy finds its way to larger scales, affecting the motion of gas in the whole galaxy - even the way it is being accreted in the galaxy."

Over time, scientific understanding of processes such as star formation has evolved, yielding new equations. The equations can in turn be used to refine the computational model. Meanwhile, computational power continues to increase, making it possible to simulate those increasingly complex models.

"We could not have done it [this simulation] just three years ago," Governato said. "The computers were just not powerful enough."

-Miriam Boon, iSGTW

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