Tracking origin of cosmic ray bursts.

There is new and compelling evidence that cosmic gamma ray bursts originate from within the Milky Way and not from the edge of the universe, as many astronomers had believed, according to University of Chicago astrophysicists Jean Quashnock and Don Lamb. For 25 years, scientists have observed these mysterious bursts of extremely high energy radiation. Because they are so brief--from less than a second to a few minutes in duration--and also appear randomly, no one has been able to determine what causes them or even how far away they are.

Scientists constantly debate whether the bursts are cosmological, from the edge of the universe, or galactic, from within the Milky Way. "Now we have strong evidence that most gamma ray bursts come from within our galaxy," Lamb maintains.

Following the launch of NASA's Compton Gamma Ray Observatory (CGRO) satellite in 1991, when astronomers looked at the data it had collected, they saw a random distribution of bursts on the sky. They had expected to see a concentration in the plane of the Milky Way, confirming the galactic hypothesis. However, the seemingly uniform distribution suggested sources far beyond the realm of our galaxy and into the reaches of the outer edge of the universe. Scientific opinion shifted toward a cosmological explanation.

Quashnock and Lamb started looking more closely at the CGRO data to try make sense of it. At first, the distribution of the bursts did appear to be totally random. Yet, when the researchers took into account the statistical uncertainties inherent in determining their exact positions in the sky, they began to see clumps of them. Some were clustered so closely together they could not be distinguished from each...