U.Chicago Flash Center to perform grueling supernova simulations using millions of hours of supercomputer time (Forwarded)

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Jan. 8, 2007

University of Chicago Flash Center to perform grueling supernova simulations
using millions of hours of supercomputer time

The University of Chicago's Center for Astrophysical Thermonuclear Flashes
will perform the world's most advanced simulations of exploding white dwarf
stars with an allocation of 2.5 million hours of processing time on the U.S.
Department of Energy's high-performance computers. The simulations will be
made possible by a DOE award called INCITE (Innovative and Novel Computation
Impact on Theory and Experiment), announced today in Washington, D.C.

"Astrophysics is one of the leading areas that is pushing the development of
the most powerful, capable computers in the world," said Flash Center
Director Don Lamb, the University's Louis Block Professor in Astronomy &
Astrophysics.

The computing-time allocation will make possible computer simulations that
could help scientists tackle the major question vexing cosmologists today:
what is the nature of dark energy, a mysterious force that dominates the
universe. Certain aspects of the simulations may also help scientists ensure
the reliability of the nation's nuclear stockpile.

The physical processes that Flash Center scientists simulate in exploding
stars -- supernovae -- overlap significantly with the physical processes of
concern to the DOE's Stockpile Stewardship Program. In compliance with the
Comprehensive Test Ban Treaty, the program seeks to ensure the U.S. nuclear
deterrent by integrating computer simulations, experiments and past nuclear
test data instead of actual detonations.

"The simulations that we're doing are similar in complexity to Stockpile
Stewardship Program simulations," Lamb said.

For this reason, the Advanced Simulation and Computing program of the DOE's
National Nuclear Security Administration has supported the Flash Center with
funds and computing time for the past nine years in its Academic Strategic
Alliance Program.

"The goal is to use the Flash Center supernova problem to drive broadly
useful advances in simulation technology," Lamb said. With the INCITE
computer program itself centered at a DOE Office of Science Laboratory, the
award serves as an example of two DOE divisions working synergistically to
advance the nation's scientific and security agendas, he said.

The Flash Center specializes in simulations of white dwarf stars. These
stars have shrunk to the size of the Earth after having burned most or all
of their nuclear fuel. When they explode, astrophysicists refer to them as
type Ia supernovae. These supernovae shine so brightly that astrophysicists
use them to measure distance in the universe and to study the nature of dark
energy.

The discovery of dark energy first made news in 1998, when two groups of
scientists who study exploding stars announced that their measurements
indicated the existence of a mysterious force that works against gravity and
seems to be accelerating the expansion of the universe. Scientists have
identified understanding the properties of dark energy as a science
priority. A better understanding of type Ia supernovae also will help
advance dark energy research, Lamb said.

Astrophysicists are striving to determine which of four possible processes
trigger these supernovae. Different processes will produce different
characteristics that astronomers can observe telescopically to help verify
their theories. "Our goal in doing these simulations is to pin down the
explosion mechanism," Lamb said.

During the next year, the Flash Center team will focus on what it considers
the most promising of the four theories, a process they call the
gravitationally confined detonation mechanism. Flash Center scientists
proposed the existence of this process based on their previous simulations.

In this process, flames ignite at one or a few confined points off-center
from the core of the star. A hot bubble forms, grows rapidly, breaks through
the surface, then spreads over the entire surface of the star at high
velocity. The flame collides with itself at the opposite end of the star,
compressing unburned material in the surface layers to high densities and
pressures and detonates.

There are only 8,760 hours in a year, but the Flash Center team will use all
2.5 million hours of its computing allocation by early January 2008 in doing
these simulations by harnessing the power of parallel computing. With the
INCITE award, the Flash Center will have the continuous use of 6,000
processors for nearly two and a half weeks on the Seaborg supercomputer at
Lawrence Berkeley National Laboratory in California.

The Flash Center's Robert Fisher compared parallel computing to a high-tech
horse-drawn chariot. "A rider on a single horse can plod along using the
power of only that horse. However, by hitching many horses to a chariot, a
charioteer can efficiently combine the power of many horses," said Fisher, a
Research Scientist at the Flash Center.

Successfully executing these lengthy, computationally intensive simulations
will require untold hours of fine-tuning the hardware, the operating system,
the software coding and other components of the process by DOE's computer
experts and Lamb's team. "There's a reason why these simulations are
referred to as 'hero calculations,' " Lamb said.

For images of a Flash Center supernovae simulation, see:
http://flash.uchicago.edu/~jbgallag/news/4km_wd_def/
[Credits: University of Chicago Flash Center]