Discovering the Origin of Stars Through 3D Simulation

06.30.16

Evolution of a giant molecular cloud over 700,000 years, from a simulation run on the Pleiades supercomputer using the ORION2 code developed at the University of California, Berkeley. Gravitational collapse leads to the formation of an infrared dark cloud (IRDC) filament in which protostars begin to develop, shown by the bright orange luminosity along the main and surrounding filaments. Visualization: David Ellsworth and Tim Sandstrom, NASA/Ames

Imagine yourself in a video game zooming back through space and time at warp speed. Along the way you are pulled by gravity, buffeted by turbulent gases and magnetic waves, and exposed to intense radiation. At 350,000 years, you witness the birth of early stars, and then warp back to the present to tell scientists what you observed. You're on the path to solving one of the most perplexing challenges for scientists today—the physical processes that form stars and star clusters in the Milky Way and beyond.

That's the scene astrophysicists at the University of California, Berkeley and Lawrence Livermore Laboratory (LLNL) are creating through first-of-a kind simulations run on the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility at Ames Research Center. Coupling real observations from the Hubble Space Telescope and other space-based observatories with their state-of-the art 3D code, ORION2, these scientists are helping experts around the globe piece together the origin of stars, stellar clusters, and the high-mass stars that form within the clusters.

"Our simulations, run on Pleiades and brought to life by the visualization team at the NAS facility at Ames, were critical to obtain important new results that match with Hubble's high-resolution images and other observations made by a variety of space and Earth-based telescopes," said Richard Klein, adjunct professor at UC Berkeley and astrophysicist at LLNL. A key result, supported by observation, is that some star clusters form like pearls in a chain along elongated, dense filaments inside molecular clouds—so-called "stellar nurseries."

Klein, along with his colleagues, professor Chris McKee and research specialist Pak Shing Li, and their students at UC Berkeley, developed the ORION2 radiation-magnetohydrodynamics code to capture the broad range of physics and the immense scales of time and space required to produce the simulations, which follow the formation and evolution of protostellar clusters across 700,000 years.

The simulations show the entire evolution of these clusters—starting with a giant molecular cloud that collapses due to gravitational forces, to the formation of multiple turbulent clumps of interstellar gas inside the cloud, which in turn collapse into stellar clusters and cores that ultimately form individual stars.

"Without NASA's vast computational resources, it would not have been possible for us to produce these immense and complex simulations that include all the output variables we need to get these new results and them compare with observations," Klein explained. The ORION2 simulations incorporate a complex mix of gravity, supersonic turbulence, hydrodynamics (motion of molecular gas), radiation, magnetic fields, and highly energetic gas outflows. The science team conducted many independent tests of each piece of physics in ORION against known data to demonstrate the code's accuracy.

The next technical challenge for the team is to incorporate more accurate initial simulation conditions derived from physical processes, at larger spatial scales. This will enable even higher resolution results with zoom-in capabilities and adaptive mesh refinement techniques. "Higher resolution in the simulations will enable us to study the details of the formation of stellar disks formed around protostars. These disks allow mass to transfer onto the protostars as they evolve, and are thought to be the structures within which planets eventually form," said Klein. Achieving this goal will require at least double the amount of processor time on Pleiades and several hundred terabytes of storage over the next couple of years.

Klein is keeping his eye on the big picture: “Understanding star formation is a grand challenge problem. Ultimately, our results support NASA's science goal of determining the origin of stars and planets, as part of its larger challenge of figuring out the origin of the entire universe."

—Jill Dunbar, NASA/Ames Research Center