ORNL heads DOE project that looks to the stars

OAK RIDGE, Tenn., – Through a newly funded Department of Energy project,
astrophysicists at Oak Ridge National Laboratory and around the United States hope
to gain a better understanding of what happens when stars die in spectacular
explosions called core collapse supernovae.

To people like ORNL astrophysicist Tony Mezzacappa, this work is about more than
just satisfying their curiosity. The project is aimed at answering some basic questions
about the origin of life.

“Life as we know it would not exist if not for these incredible explosions of stars,” said
Mezzacappa, a member of ORNL’s Physics Division. “When stars die in these
explosions that generate billions upon billions of watts of energy, elements necessary
for life are strewn throughout the galaxy and become part of the ‘soup’ from which our
solar system formed.”

The five-year $9.2 million Scientific Discovery through Advanced Computing (SciDAC)
project headed by Mezzacappa will focus on several areas, but a major thrust will be
on developing a standard model for core collapse supernovae. Modeling
requirements for this work are severe.

“The advent of computing resources capable of trillions of calculations per second
makes it possible to carry out the necessary large-scale three-dimensional
simulations to understand the supernova explosion mechanism and all the
phenomena that accompany the explosion of stars,” Mezzacappa said.

While it takes millions of years for a star to evolve, the core collapse supernova
explosion takes place in just hours. These events occur about two to three times each
century in our galaxy.

Aside from the significant computational challenges of the project, Mezzacappa notes
that this work, which draws from scientists at eight universities and the National
Center for Supercomputer Applications, has strong ties to basic research missions of
DOE.

“DOE has long been involved in both neutrino astrophysics and accelerator-based
neutrino physics,” Mezzacappa said. “This work will make important progress toward
a standard model of supernovae similar to the development of the standard model for
the sun. It also ties together much of DOE’s efforts in the areas of high-energy and
nuclear physics.”

With accurate supernovae models, neutrinos from supernovae can tell scientists
about the properties of the dense matter in a supernova.

“We want to learn about the explosion mechanism and then the composition of the
star and what that can tell us about fundamental particle and nuclear physics,”
Mezzacappa said.

Another important aspect of the work includes learning more about how stable heavy
elements are created. With this information, scientists hope to understand the chain
of events leading to the formation of life on Earth.

Also of particular interest to DOE is a collaboration with NASA and new observations
of the Earth’s cosmic ray environment. Supernovae are likely the principal source and
one of the acceleration mechanisms for cosmic rays.

“Our work addresses very broad themes important to DOE’s national mission,”
Mezzacappa said. “The ability to model the movement of radiation through matter and
its interaction with that matter is a concern not only for supernovae models but also for
people who model internal combustion engines, climate patterns and to researchers
seeking better tools for radiation therapy.”

One of the collaborators is the University of Tennessee, where distinguished scientist
Jack Dongarra and colleagues will be working on mathematical solutions
(algorithms) to help solve the equations that govern the motion of neutrinos through
the stellar material. Dongarra is also a member of a SciDAC team of computer
scientists who specialize in measuring and optimizing the performance of computer
programs.

Mezzacappa also said ORNL will be collaborating with members of the University of
Tennessee’s Joint Institute for Computational Sciences, whose expertise spans a
number of areas of interest to ORNL.

SciDAC is an integrated program that will help create a new generation of scientific
simulation computer programs. The programs will take full advantage of the
extraordinary computing capabilities of computers capable of performing trillions of
calculations per second to address increasingly complex problems.

The recently announced 51 DOE SciDAC projects will receive a total of $57 million this
fiscal year to advance fundamental research in several areas related to the
department’s missions, including climate modeling, fusion energy sciences,
chemical sciences, nuclear astrophysics, high-energy physics and high-performance
computing.

In addition to the University of Tennessee and the National Center for Supercomputer
Applications, collaborators for the project are North Carolina State University, Florida
Atlantic University, the University of California-San Diego, the University of Washington,
State University of New York at Stony Brook, Clemson and the University of Illinois at
Urbana-Champaign. Individuals involved in the project from ORNL are David Dean
and Mike Strrayer of the Physics Division and Ross Toedte of the Computer Science
and Mathematics Division.