A group led by astrophysicist
Stan Woosley is using the Columbia supercomputer to run
simulations of a "burning floating bubble" representing
a small piece of a supernova as it explodes. These images
are snapshots from the group's 2-dimensional and 3-dimensional
November 15, 2004
Scientists harness powerful new supercomputer
at NASA Ames for research on cosmology and astrophysics
By Tim Stephens
Astrophysicists and cosmologists at UCSC are among the first
scientists to have access to the powerful new Columbia supercomputer
at the NASA Ames Research Center. The UCSC scientists have been
using the new system's unprecedented computing power to run
simulations of complex phenomena such as supernova explosions,
gamma-ray bursts, and dark matter halos.
Earth sciences professor Gary
Glatzmaier provided this snapshot from a simulation on
the Columbia supercomputer of turbulent convection in
a rapidly rotating disk or equatorial plane of a star
or giant planet. Details of the image illustrate the mechanism
that likely plays a major role in maintaining the banded
zonal winds on the surfaces of Jupiter and Saturn.
NASA will be featuring the work of UCSC researchers along with
various NASA projects in demonstrations and presentations this
week at SC2004, the premier international conference on high-performance
computing, networking, and storage. The conference takes place
at the David L. Lawrence Convention Center in Pittsburgh, November
The Columbia supercomputer, named to honor the crew of the
Space Shuttle Columbia lost in early 2003, was unveiled
at NASA Ames on October 26. It has achieved a sustained performance
of 51.9 trillion operations per second, or teraflops, making
it one of the fastest supercomputers in the world, outperforming
Japan's Earth Simulator, previously the world's fastest supercomputer.
(IBM's Blue Gene/L last week clocked 70.7 teraflops and now
Jim Taft, who leads the terascale applications group in NASA's
Advanced Supercomputing Division, said access to Columbia was
determined by a NASA review committee that established a list
of prioritized activities.
"The UCSC work was at the top of the list, so we were
authorized to give early access to a number of UCSC projects.
These guys have been burning up the cycles ever since,"
The NASA exhibit at SC2004 will feature work by several UCSC
researchers, including simulations of gamma-ray bursts and nuclear
combustion in supernovae by Stan Woosley, professor of astronomy
and astrophysics, and his collaborators.
"Using this machine is like being allowed to take several
spins around the track at the wheel of the winning car at the
Indy 500. We are ecstatic about the results we are getting,"
In the supernova study, Woosley is working with postdoctoral
researcher Mike Zingale and researchers at Lawrence Berkeley
National Laboratory (LBNL) to study in minute detail how a nuclear
combustion front, or "flame," moves through a star
as it explodes in a supernova. John Bell, Marc Day, and Chuck
Rendleman are combustion scientists at LBNL who provided computer
code for simulating flames that Zingale applied to the astrophysics
"It is novel having combustion scientists and astrophysicists
working together this way, and it is an indication of the difficulty
of the problem," Woosley said. "To our knowledge,
this is the largest, highest resolution study ever done of nuclear
combustion in a thermonuclear supernova."
Type Ia supernovae are the brightest thermonuclear explosions
in the universe, as bright as 10 billion suns, and they have
become important as "standard candles" used to measure
the size and expansion of the universe. The explosion begins
as a few hot spots near the center of a white dwarf star, generating
far more energy than convection or diffusion can dissipate.
Carbon and oxygen fuse to form heavier elements, chiefly iron,
and the temperature rises to 10 billion degrees Kelvin. Since
the ash is lighter than the surrounding fuel, bubbles form that
float away, burning violently as they go.
Over the next second, most of the star is consumed, releasing
enough energy to explode as a supernova. The properties of the
explosion, including its brightness, are determined by the rate
of nuclear fusion during that critical second, and a calculation
based on "first principles" has eluded astrophysicists
for decades because the flame is subject to a variety of instabilities
that are tricky to model. The range of length scales is also
enormous, from the one-millimeter thickness of the flame to
the 2,000 kilometer radius of the star.
Woosley's group is simulating floating bubbles bounded by a
carbon fusion front propagating in an essentially infinite reservoir
of fuel. Only a small piece of the entire supernova is carried
in the calculation. These simulations are quite complex and
only a massively parallel computer with a lot of memory is capable
of doing the calculation. On Columbia, the researchers are able
to run this simulation long enough to see the complexities in
the evolution develop. This simulation has already grown so
large that they would have been unable to carry it out on any
other machine, Woosley said.
"The complexity of NASA's space-derived data have become
so great that tools of this sort need to be developed to make
sense of it all," Woosley said. "We expect numerical
simulation will increasingly dominate theoretical astrophysics
in the coming years. For better or worse, we have moved beyond
the ability to solve the most important problems using pencil
and paper alone."
Brandon Allgood, a graduate student working with UCSC professor
of physics Joel Primack, was at the NASA exhibit at SC2004 last
week to describe the dark matter simulation he has been running
on Columbia. A video derived from the results of the simulation
was shown at the NASA exhibit.
"This simulation is being used to understand the formation
histories and current shapes of the dark matter halos around
galaxies," Allgood said.
Dark matter--mysterious particles that make up at least 90
percent of the universe--has shaped the evolution of the universe
through its gravitational pull on the ordinary, observable matter
of galaxies and stars. Galaxies formed within large halos of
dark matter, and the clumping of dark matter, also guided the
formation of galaxy clusters and other large-scale structures
in the universe.
Primack has been using dark matter simulations to model the
evolution of structure in the universe for many years. His group's
latest simulation completed its run in less than a week using
just a fraction of Columbia's processing power. Primack said
he had been unable to get enough time to run the simulation
on a Department of Energy supercomputer, where it would have
taken over a month to run the same code.
"We're very excited to have early access to this supercomputer.
We are now running an even bigger and more ambitious project
than the one that will be on display at the conference,"
Other UCSC projects running on the Columbia machines are led
by Gary Glatzmaier, professor of Earth sciences, and Piero Madau,
professor of astronomy and astrophysics. Glatzmaier's group
is studying complex processes in the deep interiors of stars,
like the Sun, and large "gas giant" planets, like
Saturn. Madau and graduate student Michael Kuhlen are studying
the early evolution of the universe with a simulation that follows
the cosmological coevolution of dark matter and primordial gas.
A bioinformatics group led by David Haussler, professor of biomolecular
engineering and a Howard Hughes Medical Institute investigator,
is also using Columbia for research on the evolution of the
Columbia is a highly integrated cluster of supercomputers driven
by 10,240 Intel Itanium 2 processors. It comprises 20 identical
nodes, each with 512 processors and one terabyte of shared memory.
The benchmark performance of 51.9 teraflops was achieved using
20 nodes, and Columbia's peak performance is rated at 61 teraflops.
The Columbia system was integrated in 120 days and the supercomputer
is now fully operational with more than 650 users.
For more information about the Columbia supercomputer, see
For more information about SC2004, see www.sc-conference.org/sc2004/.
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