Interstellar mystery solved by simulation

Interstellar mystery solved by simulation
An interstellar mystery of why stars form has been solved thanks to the most realistic supercomputer simulations of galaxies yet made. Theoretical astrophysicist Philip Hopkins of the California Institute of Technology (CalTech) led research that found that stellar activity — like supernova explosions or even just starlight — plays a big part in the formation of other stars and the growth of galaxies.
“Feedback from stars, the collective effects from supernovae, radiation, heating, pushing on gas, and stellar winds can regulate the growth of galaxies and explain why galaxies have turned so little of the available supply of gas that they have into stars,” Hopkins said.

Galaxy simulations were tested on the Stampede supercomputer of the Texas Advanced Computing Center (TACC), an Extreme Science and Engineering Discovery Environment-allocated (XSEDE) resource funded by the National Science Foundation.

The initial results were published September of 2014 in the Monthly Notices of the Royal Astronomical Society. Hopkins’s work was funded by the National Science Foundation, the Gordon and Betty Moore Foundation, and a NASA Einstein Postdoctoral Fellowship.
The mystery begins in interstellar space, the vast space between stars. There dwell enormous clouds of molecules, mainly hydrogen, with the mass of thousands or even millions of Suns. These molecular gas clouds condense and give birth to stars.
What’s puzzled astrophysicists since the 1970s is their observations that only a small fraction of matter in the clouds becomes a star.
The best computer simulations, however, predicted nearly all of a cloud’s matter would cool and become a star. “That’s really what we were trying to figure out and address, for the first time, by putting in the real physics of what we know stars do to the gas around them,” Hopkins said.

A multi-institution collaboration formed with members from CalTech, U.C. Berkeley, U.C. San Diego, U.C. Irvine, Northwestern, and the University of Toronto. They produced a new set of supercomputer galaxy models called FIRE or Feedback in Realistic Environments. It focused the computing power on small scales of just a few light years across. “We started by simulating just single stars in little patches of the galaxy, where we trace every single explosion,” Hopkins explained. “That lets you build a model that you can put into a simulation of a whole galaxy at a time. And then you build that up into simulations of a chunk of the universe at a time.”
Hopkins developed the simulation code locally on a cluster at CalTech, but the Stampede supercomputer did the lion’s share of the computation.
The University of Texas at Austin
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