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September 17, 2001

DOE grant creates Center for Supernova Research based at UCSC

By Tim Stephens

Massive exploding stars called supernovae are among the most spectacular phenomena in the universe. Astrophysicists, however, are still struggling to work out the mechanics of these awesome explosions. A team of astrophysicists and computer scientists at UCSC and three other institutions is now tackling the problem with support from a $2 million, three-year grant from the Department of Energy (DOE).

This is a simulation of the density profile of a 1 solar mass main sequence star (just like the sun) after shock wave passage from a Type Ia supernova (which "went off" above the top of the image). The blue colors represent the density of the "core" of the main sequence star, green is less dense material from the envelope, yellow is material being stripped from the envelope, red is the background density after the supernova shock has passed. Image: Lawrence Livermore National Laboratory
The grant establishes a Center for Supernova Research headquartered at UCSC. Stanford Woosley, professor and chair of astronomy and astrophysics, is principal investigator and director of the new center. The other partner institutions are the University of Arizona and the Los Alamos and Lawrence Livermore National Laboratories.

"The goal is to build realistic numerical models of exploding stars, using the fastest computers available to simulate the explosions," Woosley said.

The grant is funded by the DOE's new Scientific Discovery through Advanced Computing (SciDAC) program, which aims to address complex scientific problems by taking advantage of the extraordinary computing capabilities of terascale computers (computers capable of doing trillions of calculations per second). The supernova researchers will be using several powerful supercomputers, including those at the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory and the Accelerated Strategic Computing Initiative at Lawrence Livermore National Laboratory. The researchers will also use a large "Beowulf" computing cluster to be built at UCSC this fall.

"Almost all of modern physics comes to bear in a supernova explosion--radiation transport, fluid dynamics, thermonuclear fusion, and so on," Woosley said. "We know the basic equations, but putting all of that together to create a multidimensional simulation of a supernova is something you can't do without a lot of computing power."

A supernova occurs when the core of a star collapses under the gravitational force of its own mass. This can happen in a binary star system when mass is transferred between two closely orbiting stars, resulting in what is known as a type 1 supernova. The other basic type of supernova, type 2, occurs at the end of the lifetime of a single massive star, when its nuclear fuel is exhausted.

A supernova explosion can be as bright as an entire galaxy, releasing immense amounts of energy. The explosion also spews into space all of the chemical elements forged by nuclear fusion reactions during the life of the star and some that are formed during the explosion itself. These materials may then contribute to the formation of new stars and planets. Thus, supernovae are ultimately responsible for the rich array of elements that populate the periodic table.

In the past, researchers have been limited to modeling supernovae in one or two dimensions, Woosley said. "But nature makes supernovae in three dimensions, and the explosions are not perfect spheres," he said. "We see all sorts of clumpiness and structure, so we want to build computer modeling capabilities commensurate with those observations."

When the results of a computer simulation look like the observational data astronomers gather from real supernovae, the modelers know they are on the right track. Realistic models of supernovae can be powerful tools for understanding the evolution of stars and the abundances of heavy elements. The models can also help researchers interpret observational data.

The DOE's SciDAC program is funding 51 projects this year in areas ranging from climate modeling to high-energy physics. The Center for Supernova Research is one of two SciDAC projects that will be investigating supernovae. The other supernova project is led by Oak Ridge National Laboratory.

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