Raw Data: Why Stars Blow Up

A star one second, an exploding supernova the next

By Jessica Ruvinsky|Sunday, May 28, 2006

THE STUDY "A New Mechanism for Core-Collapse Supernova Explosions," published in the April Astrophysical Journal. The aim is to understand how a collapsing star can, in a single second, ignite into a supernova and explode like a trillion trillion trillion gallons of jet fuel.

THE PROBLEM Supernovas sculpt the universe—they help spawn new stars and created the calcium in your bones, the iron in your blood, and the fluorine in your toothpaste—yet nobody really knows what sets them off. "The supernova explosion mechanism is one of the major unsolved problems in astrophysics," says Adam Burrows of the University of Arizona.

THE FINDINGS Scientists understand how supernovas work right up to the boom. A massive star shines for about 10 million years, accumulating a nuclear ash pile until it hits a critical mass. In less than a second the core collapses, becoming 100 trillion times as dense as water,and immediately bounces back. But the shock of the bounce is not enough to make the star detonate. What sends a supernova over the edge is a mystery.

Burrows and his colleagues used a computer program called VULCAN/2D to simulate the violent death of a star 11 times the mass of the sun. The virtual star is divided into 30,000 to 50,000 pieces. The program calculates the velocity, density, and energy of each of those pieces, allows a moment of simulated time to pass, and repeats the process. Each step represents just one-millionth of a second of the star's life.

The researchers had to run VULCAN/2D on 48 AMD Opteron processors for two months just to simulate the evolution of the star from 0.2 second before the bounce until 0.66 second after.

The supernova's secret ingredient may be sound. Burrows's simulation shows that 0.5 second after the bounce, hot matter falling inward makes the star's 36-mile-wide inner core vibrate. The core oscillates 300 times per second, sending out sound waves a little higher than middle C on a piano, which zoom through the star at 70 million miles per hour. The note heats up and pushes on the core's outer shell until the intensity of the sound causes the star to explode.

THE RESEARCHER Adam Burrows is something of a human computer, swiftly converting kilometers per second into miles per hour in his head, although the speed of his calculations "depends on whether I've eaten." For this paper he knew one brain was not enough, so he joined forces with researchers in Israel and Germany as well as colleagues at the University of Arizona. He expects his picture of musical supernovas "will certainly shake up the community," but he is his own greatest skeptic: "Whether it's true remains to be seen."

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