- WASHINGTON (AP) - The most powerful explosion ever witnessed - a gamma ray
burst 12 billion light years distant - released in one second almost as
much energy as all the stars of the universe, astronomers said Wednesday.
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- It was too far away to affect the Earth
or the sun, but the astronomers said they were astounded by the might of
the blast and mystified about what astronomical process could have caused
it.
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- ``The energy released by this burst in
its first few seconds staggers the imagination,'' said Shrinivas Kulkarni,
a professor of astronomy at California Institute of Technology and leader
of a team that helped calculate the explosion size.
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- Kulkarni is co-author of a study being
published Thursday in the journal Nature. He and others appeared at a Washington
news conference Wednesday.
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- Gamma ray bursts are common, occurring
once or twice a day, but the rays are invisible and can be detected only
by satellites orbiting above the Earth's atmosphere. Since a burst lasts
only seconds, astronomers rarely are able to focus telescopes on the source
and capture light measurements needed to calculate the size of the explosion
or pin down its location.
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- But on the night of Dec. 14, an Italian
team detected a gamma ray burst with the BeppoSAX orbiting observatory
and quickly alerted David J. Helfand, a Columbia University astronomer.
Helfand relayed the information to astronomers operating telescopes at
Kitt Peak near Tucson, Ariz. , who were able to photograph the source site
of the burst.
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- Later, the Hubble Space Telescope and
others captured views of the explosion's afterglow, which was in visible
light. The studies revealed the source as a very faint and distant galaxy.
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- 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 5.9 trillion miles. This great distance meant that the explosion
was immensely powerful, Kulkarni said.
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- ``I was astounded when I heard these
results,'' said Stan Woosley, a professor of astronomy at the University
of California, Santa Cruz, and an expert on astronomical explosions. ``This
was the brightest documented explosion in history.''
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- 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. In visible
light alone, Woosley said, the gamma ray burst energy was equal to about
1,000 supernovae.
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- By some calculations, the gamma ray burst
release equaled as much energy in one second as all of the 10 billion trillion
stars in the universe combined.
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- Woosley said it is difficult to relate
the power to common terms. For instance, he said, if all of the nuclear
weapons ever made were exploded at once, the energy released would equal
about 1/100,000 of a second of the energy from Earth's sun. Yet, over its
10 billion-year history the sun will produce only about 1 percent of the
energy of the gamma ray burst, the astronomer said.
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- Gamma ray bursts were unknown until the
launch of U.S. military satellites designed to detect radiation from the
explosion of atomic bombs.
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- Later, scientific satellites were launched
to study the bursts, but astronomers remained mystified.
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- ``We had no idea where they came from
or what was responsible for them,'' said Alan Bunner, a science program
director at NASA.
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- More than 2,000 of the brief bursts have
been recorded, but astronomers were unable until recently to pinpoint their
location or measure their distance from Earth. The location of three has
been determined.
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- Kulkarni said all the bursts have been
located in dusty regions where stars form, suggesting the massive explosions
may play a role in the birth of new stars.
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- Woosley and others speculate that the
explosion may occur when a black hole swallows a neutron star. A black
hole is a collapsed object that is so dense that its gravity permits not
even light to escape, and a neutron star is a massive collapsed star. Woosley
acknowledged the explanation remains only speculation.
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- Astronomers believe the immense explosion
just detected sent matter, such as neutrons and electrons, streaking outward
at near the speed of light. About a day later, the matter smashed into
gas and dust particles. The violence and heat of the collision created
gamma rays, X-rays, then visible light.
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- It was these energy sources detected
by the orbiting instruments and later by the telescopes.
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