

Los Angeles Times
Published Thursday, October 06, 2005


When two of the super-dense, burned-out stars slam into each other, they emit gamma rays that release more energy in a fraction of a second than the sun has produced in its entire history, according to a series of papers published Thursday in the journal Nature.

"Our observations do not prove the ... model, but we surely have found a lady with a smoking gun next to a dead body," said California Institute of Technology astronomer Shri Kulkani, who co-authored one of the papers.

The first big clue came in May, when the National Aeronautics and Space Administration's Swift spacecraft captured evidence of a fleeting burst of gamma rays.

Although it lasted only 70 milliseconds, it was followed by a stream of X-rays that for the first time allowed scientists to trace their source, said Don Lamb, a professor of astronomy and astrophysics at University of Chicago and author of one of the papers.

They calculated that the gamma rays came from the edge of a galaxy 1 billion light-years from Earth. Although the X-rays were too faint to determine the exact location of the burst, the evidence supported the theory that a neutron star collision was responsible.

For better proof, they would have to wait for a brighter gamma-ray burst.

It came two months later. That burst also was finished in 70 milliseconds, but it was much brighter and produced a bigger stream of X-rays. Telescopes on Earth and in orbit were able to pinpoint its location to the outskirts of a spiral galaxy, also about 1 billion light-years away.

The location was important because it ruled out a prime candidate -- supernovas, which are found toward the center of galaxies.

The only other possibility was neutron stars, the collapsed remnants of supernovas, propelled by their explosions out to the fringes of galaxies.

Some of these neutron stars wind up in pairs, circling each other for tens of millions or even billions of years as gravity pulls them together.

The eventual collision produces gas jets that stream out in two directions and are recognized on Earth as gamma rays, the highest-energy form of electromagnetic radiation.

Although satellites and telescopes did not observe the collision directly, scientists said the evidence builds a solid case for the collision theory.