Lawrence Livermore National Laboratory supercomputing expertise helped University of Chicago scientists take an important step toward revealing the secrets of dark energy by blowing up a white dwarf star in a three-dimensional simulation of unprecedented details.
Cal Jordan/University of Chicago Flash Team - Images from a computer simulation of an exploding white dwarf star. The orange represents the flame that nuclear ash follows as it pops out of the star, while the blue approximately marks the surface of the star. The star is approximately the size of the Earth, but contains a mass greater than the sun's. The images come from a simulation that will be presented at the "Paths to Exploding Stars" conference on March 22 in Santa Barbara, Calif., by University of Chicago scientists. See here to view movies.
The 3D simulation was conducted by a team at the University of Chicago’s Center for Astrophysical Thermonuclear Flashes (Flash Center) with assistance from computer scientists at the U.S. Department of Energy’s (DOE) National Nuclear Security Administration (NNSA). The simulations were run on high performance computers at Lawrence Livermore and Lawrence Berkeley National Laboratories.
Computing resources and funding support for these Flash Center simulations were provided for nearly a decade by NNSA’s Advanced Simulation and Computing (ASC) Program and from the DOE Office of Science’s Innovative and Novel Computation Impact on Theory and Experiment (INCITE) Program for computer cycles.
University of Chicago scientists discussed the breakthrough simulation at the “Paths to Exploding Stars” conference in Santa Barbara March 22. Through a better understanding of how a type 1a supernova explodes, astrophysicists hope to gain insight into the mystery of dark energy, an unknown force pushing apart the cosmos that accounts for two thirds of the aggregate energy in the universe. Type 1a supernovae are used as “standardizable candles” to determine the distance and acceleration of distant galaxies; consequently it’s important to understand their output accurately.
This series of images shows a two-dimensional slice through the center of an exploding white dwarf star. The lines that form the rings are contours that mark differences in density. The gray tones represent fuel and ash that is enveloping the star. These images were produced in the first three-dimensional computer simulation in which a white dwarf exploded naturally. In previous 3D simulations, the detonation had to be inserted manually.
“This trailblazing achievement demonstrates the value of multidisciplinary academic alliance collaborations in delivering breakthrough simulations that advance basic science, scientific computing and national security,” said Dimitri Kusnezov, head of NNSA’s ASC program. “Alliances with academia are accelerating the development of new computational technologies and helping to train the next generation of scientists for work in national labs, industry and research universities.”
Understanding the physics of thermonuclear burn, such as that in supernovae, is of great interest to NNSA scientists responsible for ensuring the safety, security and reliability of the nation’s nuclear stockpile in the absence of underground nuclear testing. Nuclear testing, which ended in 1992, has been replaced by a science-based regime of large integrated computer simulation and surrogate experiments called Stockpile Stewardship. NNSA supports science relevant to its national security missions through academic alliances, notably in the area of computation.
The success of this simulation has broad implications for the role of type 1a supernovae as distance markers for cosmology, according to Stephen Libby, a physicist at Lawrence Livermore who has served as a liaison with the Chicago Flash Center. “Nobody has been able to simulate a white dwarf blowing up before without cheating: inserting some data into the process,” Libby said. “But what they’ve succeeded in doing here is a simulation without cheating. Using their ASC and INCITE simulations and research they found a mechanism for making a full 3D detonation. This is a remarkable achievement.”
“The amount of work was huge and required multiple disciplines,” he said, noting the simulation required large amounts of computer time to run. “Making these simulations run efficiently for weeks on end was a tour de force.”
Some of the simulation work was run on the Livermore uP supercomputer, the unclassified piece of the ASC Purple system. ASC Purple is an IBM system currently ranked number four on the Top500 list of the world’s most powerful supercomputers. Livermore Computing Center computer scientists assisted in making the Flash code run efficiently during the long simulation runs.
Initiated in 1997, ASC’s Academic Alliance Program has established centers for advancing simulation science at Caltech, Stanford University, University of Illinois Urbana/Champaign, and Utah, in addition to the University of Chicago. Each of these centers has made major advances in large-scale simulation on complex ASC class unclassified problems of national interest. With these advances in high performance scientific computing, the academic alliance program is evolving into its next phase as the Predictive Science Academic Alliance Program, which is intended to establish new computational science centers focused on predictive science via large-scale, verified and validated simulations.
