this is how it will end:
-- "Live" gamma burst was huge, astronomers say --
By Maggie Fox, Health and Science Correspondent
WASHINGTON, March 25 (Reuters) - The first gamma-ray burst
that astronomers got to watch "live" was the biggest explosion
ever seen, second only to the "big bang" that gave birth to the
universe, they said on Thursday.
The burst of energy, caught on camera with the help of a
complex link of satellites, telescopes and e-mail, came from
the far reaches of the universe, sending light, X-rays and
radio waves two-thirds of the way across the universe.
But it probably looked so intense because it came as a beam
of energy, rather than in an explosion in all directions, the
international team of astronomers said in a series of reports.
Nonetheless, the explosion -- probably caused by the birth
of a black hole, or by the collision of two massive stars known
as neutron stars -- was so enormously powerful that it
projected its energy across nine billion years worth of time
and space.
Gamma ray bursts have long mystified astronomers. First
seen by accident in the late 1960s by U.S. scientists looking
for Soviet nuclear weapons tests in space, they come without
warning and only the fading afterglow could be detected.
But thanks to a system set up by NASA and European
scientists working with teams at various universities, on the
morning of January 23 orbiting detectors caught the burst and
within seconds signaled a computer that in turn woke up an
observatory in New Mexico and caught the explosion on film.
"It's like the difference between watching two cars collide
and coming on the accident scene several hours later," said
physics professor Carl Akerlof of the University of Michigan.
What they saw was bright.
"If you had been gazing at that spot with binoculars, you
would have seen a 'star' appear, brighten, and fade within
minutes, an unbelievably violent event from the very edge of
our universe," Galen Gisler, an astrophysicist at Los Alamos
National Laboratory in New Mexico, said in a statement.
In a series of papers published in the journals Nature and
Science, the teams of scientists described what they saw.
Shrinivas Kulkarni, an astronomer at the California
Institute of Technology (Caltech), and colleagues looked at the
"redshift" of the star -- which tells how much the light has
been faded and changed as it traveled trillions of miles (km)
to reach the Earth.
The redshift is 1.6, which means the burst was very far
away and thus extremely powerful.
"It is 70 percent of the age of the universe," Kulkarni
said. "So if you think the universe is 12 billion years old,
this is about nine billion years old."
That also makes it nine billion light years away -- a light
year being equal to the distance light travels in one year at a
speed of 189,000 miles (300,000 km) a second, or a total of
about 5.9 trillion miles (9.5 trillion km).
This alarmed astronomers. "The object would be so bright
that for the 100 seconds it was on, it outshone the whole
universe, which to me is an amazing concept," Kulkarni said.
"We were stunned," Caltech's George Djorgovski added in a
statement. "This was much further than we expected."
But the idea is not so alarming if the energy was
concentrated in a beam, like a laser. And other teams found
evidence of this.
Alberto Castro-Tirado of the Laboratorio de Astrofisica
Espacial y Fisica Fundamental in Madrid, Spain and an
international team of colleagues found the light faded in a way
that did not look like a fireball-type burst.
Jens Hjorth and colleagues at the University of Copenhagen
in Denmark found that the light from the burst, dubbed GRB
990123, was hardly polarized at all -- surprising if it had
passed through the magnetic field created by a fireball but not
surprising if it came in a beam.
In turn, this fits in with the idea of a super massive star
collapsing on itself to form a black hole, Kulkarni said.
"We think that when very massive stars die, they form a
black hole and when the debris rains in on the black hole, you
get a gamma-ray burst," he said.
"It's not an unreasonable assumption," Akerlof said in a
separate interview. But it could be something else.
"The first thing that came to mind when it was obviously
cosmological is that this would be a binary pair of neutron
stars that would spiral into each other," he added.
"If you have something spinning, it is easier for it to go
out from the axis of spin than from the sides."
The only way to know more, he said, will be to look for
more gamma-ray bursts and study them.
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