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The "Multidimensional Simulations of Core Collapse Supernovae" project was awarded 16 million processor hours in 2008.
You may be a homebody, but your atoms have been around. The calcium in your bones, the oxygen that keeps you alive, and the iron that ferries oxygen through your bloodstream were produced at billions of degrees in stars that self-destructed billions of years ago. Stars do not just light the night sky; they also act as element factories, taking the primordial hydrogen produced by the Big Bang more than 13 billion years ago and turning it into the building blocks of worlds. The lightest nuclei fuse to become progressively heavier elements; hydrogen becomes helium, which becomes carbon and oxygen, which become silicon, on up the line. Elements heavier than iron take different paths, but they still take them inside stars. "The Big Bang left the universe with hydrogen, helium, and a little bit of lithium," explains Oak Ridge National Laboratory astrophysicist Raphael Hix. "Everything heavier than that has been made since then through a stellar process." Hix has made a specialty of understanding these processes, known as nucleosynthesis. The study must answer two critical questions: How were the elements produced, and how did they get distributed? Our own sun, for example, also produces new elements, but they will not be available for new worlds. Instead, the sun will end its existence drifting through space as a slowly cooling mass of carbon and oxygen. To seed new worlds, a star must blow up. Hix pursues his investigations through simulation, using computers as modest as an office work station and as grand as ORNL's Jaguar supercomputer, the world's most powerful open science machine. He is active in a variety of collaborations and is a co-principal investigator of the project "Multidimensional Simulations of Core Collapse Supernovae." The project—awarded 16 million processor hours in 2008 through the Department of Energy's Innovative and Novel Computational Impact on Theory and Experiment program—models massive stellar explosions, with Hix's contribution focusing on element creation. By comparing the distribution of elements produced in the model with those observed in supernovas, Hix and his colleagues hope to fine-tune their model, which must accurately simulate the destruction of a star 10 to 20 times the mass of the sun and as large as the Earth's orbit around the sun. The team eagerly anticipates the arrival in the next year or so of systems able to perform more than 1,000 trillion calculations—known in the field as "petascale" systems. With such systems, Hix said, the collaboration hopes to be able to model all the isotopes created in a supernova and give us a better idea of how we came to be as we are. "If you say the word 'universe' to somebody, they picture the starry sky at night," Hix says. "But actually, the universe is right here. Our bodies, as individual atoms, have been through extremes of temperatures, billions of degrees. It had to be to get here. Without those processes, we would not be here. And so the universe is here—it's sitting in this room."—Leo Williams |
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