(Reprinted from an article by the Associated Press)

The most powerful explosion ever witnessed - a gamma ray burst 12 billion light years away - released in one second almost as much energy as all the stars in the universe, astronomers said Wednesday. It was too far away to affect the Earth or the Sun, but the astronomers said they were astounded by the size of the blast and mystified by what could have caused it.

"The energy released by this burst in its first few seconds staggers the imagination," said Shrinivas Kulkarni, professor of astronomy at California Institute of Technology and leader of the team that helped calculate the explosion's size.

Gamma ray bursts are common, occurring once or twice a day, but the rays are invisible and can be detected only by satellites orbiting about the Earth's atmosphere. Since such bursts last only seconds, astronomers are rarely able to focus telescopes on the source and capture light measurements needed to calculate the size of the explosion or pin down its location.

But on the night of December 14, 1997, an Italian team detected a gamma ray burst with the SeppoSAX orbiting observatory and quickly alerted David Helfand, a Colombia University astronomer. Helfand relayed the information to astronomers operating telescopes near Tucson, Arizona, who were able to photograph the source site of the burst.

Later, the Hubble Space Telescope and others captured views of the explosion's afterglow in visible light. The studies revealed the source as a very faint and distant galaxy.

Kulkarni and others analyzed the energy and light released from the object and concluded it was about 12 billion light-years away. A light year, the distance light travels in a year, is about 6 trillion miles.

This great distance meant that the explosion was immensely powerful, Kulkarni said. "I was astounded when I heard these results," said Stan Woosley, and expert on astronomical explosions. "This was the brightest, documented explosion in history."

Woosley said the total energy release was equal to about 5 billion supernovae, exploding stars that previously provided the most powerful documented sudden releases of energy.

By some calculations, the gamma ray burst released as much energy in one second as all of the 10 billion trillion stars in the universe combined.

Over its 10 billion-year history the Sun will produce only about one percent of the energy of the gamma ray burst, he said.

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