Second biggest 'bang' is detected Blast at far side of universe ignites scientific debate


WASHINGTON -- A stupendous explosion at the farthest reaches of the universe has dazzled Earth's astrophysicists and ignited a storm of debate about what could have caused such a blast.

"The theorists are fleeing for shelter," said John Norris Bachall of the Institute for Advanced Study in Prince-ton, N.J.

The blast was detected as a burst of high-energy gamma rays that reached Earth on Dec. 14 -- the latest of some 2,000 mysterious gamma ray bursts that scientists have detected from all parts of the universe in recent years.

But this time, thanks to the new European orbiting observatory BeppoSAX, astronomers were able to zero in on the source of the burst and calculate its distance.

When they swung the Hubble Space Telescope around to look, they were astonished to see a faint galaxy 12 billion light-years away -- near the edge of the visible universe.

To see so much energy after it has traveled from so far away implied a mind-boggling explosion. Astronomers needed a truckload of superlatives to convey its dimensions.

"For about one or two seconds, this burst was as luminous as all the rest of the entire universe," said George Djorgovski of the California Institute of Technology, a principal investigator on the discovery team.

David Helfand, a professor of astronomy from Columbia University who took part in the discovery, called it the biggest explosion ever measured by science, second in size only to the "big bang."

Most scientists believe the big bang some 14 billion years ago was the origin of all matter, space and time.

Stan Woosley, an astronomy professor at the University of California at Santa Cruz, equated the flash of energy to a billion Milky Way galaxies or a million quasars -- among the most energetic objects in the universe -- all packed into a space 100 miles across.

The discovery, by a team from Caltech, Columbia University and Dartmouth College, will be published in today's issue of the journal Nature.

Gamma rays are generated by the most violent events in the universe. But they are absorbed by Earth's atmosphere, so they can't be detected from the ground.

In the 1960s, military satellites launched to watch for gamma rays from illegal nuclear blasts on the ground began to detect them arriving from space.

After the data were declassified, astronomers jumped in and determined they did not seem to be coming from within our Milky Way galaxy, but appeared to be coming from all directions.

It was not until the launch of BeppoSAX two years ago that scientists were able to pinpoint the bursts, and more recently link them with objects whose distances could be measured.

Knowing both brightness and distance, astrophysicists could finally calculate how much energy was being released.

Scientific debate about possible origins for the bursts is heating up. Some scientists say the answers will reveal a whole new class of physics. Others say the events are more easily explained.

One theory suggests a fatal dance involving two incredibly dense objects -- a neutron star and a stellar black hole.

A neutron star is the collapsed remnant of a sun-like star that has exhausted its nuclear fuel and shrunk to a small, but extremely dense, orb of neutrons.

A stellar black hole is what's left of an even more massive star that has collapsed into an object so dense that its gravity imprisons everything that comes near enough, even light.

Woosley suggested that a neutron star orbiting a black hole might have been drawn into the black hole's whirlpool and flattened into an accelerating disk.

The system may have become, in effect, a gigantic particle accelerator that finally converted much of the neutron star's mass to energy in a titanic blast, he said.

These bursts are being detected at the rate of one or more a day, but at vast distances.

Woosley said such an event occurs in our own Milky Way galaxy once in 10 million years, briefly shining as brightly as the sun, with little effect on life here.

But a nearby blast could shower the planet with gamma rays, with potentially devastating environmental effects. Some scientists have suggested links between nearby gamma ray bursts and the mass extinctions that have punctuated Earth's history.

Whatever causes the blasts, the experts seem to agree that neutrons, electrons and protons are blasted away at nearly the speed of light.

Astronomers believe that the gamma rays are generated when the particles racing away from the blast ram into the galaxy's dust and gas.

Shrinivas R. Kulkarni, a Caltech astronomer who participated in the observations, said Hubble's photos of the blast's fading glow revealed a galaxy with lots of dust and gas. Which suggests an environment that, 12 billion years ago when the observed light from that galaxy departed for Earth, was busy with star birth.

"Our conclusion is that gamma ray bursts may have something to do with star formation in the very distant past," he said.

Pub Date: 5/07/98

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