A monstrous and mysterious explosion in distant space - a blast rivaling the power of the Big Bang that gave birth to the universe itself - has been detected by an international team of astronomers.

So massive was the blast, that for seconds it was as luminous as all the stars and galaxies in the universe, scientists said. The flash also raises myriad questions - among them, whether astronomers must now change or discard their models of the life and death of stars."The energy released by this burst in its first few seconds staggers the imagination," said Shrinivas Kulkarni of the California Institute of Technology, leader of a team that helped calculate the explosion size. Kulkarni is also the co-author, with Caltech Professor George Djorgovski, of a study being published Thursday in the British scientific journal Nature.

"It is such an extreme phenomenon that it is possible we are dealing with something completely unanticipated and even more exotic," he said.

Kulkarni, who along with other researchers described their findings at a Washington, D.C., news conference held by NASA Wednesday, said the cosmic flash was detected Dec. 14 in the direction of the constellation Ursa Major, the Big Bear.

Two orbiting satellites were the first to pick up its intense radiation: an Italian-Dutch X-ray instrument called Beppo-SAX, which can track such bursts well enough to direct ground-based astronomers using telescopes and the American Compton Gamma Ray Observatory.

An Italian team, upon detecting the flash, immediately alerted David J. Helfand, a Columbia University astronomer. By e-mail and by telephone, the message was swiftly relayed to astronomers operating telescopes at the Kitt Peak Observatory in Arizona, at the Keck II telescope atop Mauna Kea in Hawaii and by a team controlling the Hubble Space Telescope in orbit around Earth.

What the Hubble telescope and others captured was the afterglow of an exploding object - barely 100 miles in diameter - known as a gamma ray burster. Bursters primarily emit invisible, extremely short-wave electromagnetic radiation. Remaining bits of gamma ray energy emerge as X-rays, or visible light.

More than 2,000 of these bursts have been recorded, but astronomers were unable until recently to pinpoint their location. After months of analysis by several scientific teams it became clear, researchers said Wednesday, that the December burster was the most powerful ever documented. "It was as bright as at least a billion Milky Way galaxies," Stan Woosley, professor of astronomy and astrophysics at the University of California at Santa Cruz, told the news briefing.

Designated as GRB971214, the explosion was located in an extremely faint galaxy an estimated 12 billion light years away. With a single light-year equivalent to about 6 trillion miles, that places the burst near the outer edge of the visible universe, noted scientist Alexei Filippenko. Filippenko, an astronomer at the University of California at Berkeley who caught the burst's image with the Keck telescope in Hawaii, said the flash took 12 billion years to reach Earth's vicinity.

"We're looking back in time at an explosion that took place when the universe was only 10 to 15 percent of its current age," he said, "so we're probing conditions that must have existed during the universe's earliest times."