NASA Satellite
Detects Record Gamma Ray Burst Explosion Halfway Across Universe
(20 March 2008) A powerful stellar
explosion detected March 19 by NASA's Swift satellite has shattered the record
for the most distant object that could be seen with the naked
eye.
The explosion was a gamma ray burst. Most gamma ray bursts
occur when massive stars run out of nuclear fuel. Their cores collapse to form
black holes or neutron stars, releasing an intense burst of high-energy gamma
rays and ejecting particle jets that rip through space at nearly the speed of
light like turbocharged cosmic blowtorches. When the jets plow into surrounding
interstellar clouds, they heat the gas, often generating bright afterglows.
Gamma ray bursts are the most luminous explosions in the universe since the big
bang.
"This burst was a whopper," said Swift principal investigator Neil
Gehrels of NASA's Goddard Space Flight Center in Greenbelt, Md. "It blows away
every gamma ray burst we've seen so far."
Swift's Burst Alert Telescope
picked up the burst at 2:12 a.m. EDT, March 19, and pinpointed the co-ordinates
in the constellation Boates. Telescopes in space and on the ground quickly
moved to observe the afterglow. The burst is named GRB 080319B, because it was
the second gamma ray burst detected that day.
Swift's other two
instruments, the X-ray Telescope and the Ultraviolet/Optical Telescope, also
observed brilliant afterglows. Several ground-based telescopes saw the
afterglow brighten to visual magnitudes between 5 and 6 in the logarithmic
magnitude scale used by astronomers. The brighter an object is, the lower its
magnitude number. From a dark location in the countryside, people with normal
vision can see stars slightly fainter than magnitude 6. That means the
afterglow would have been dim, but visible to the naked eye.
Later that
evening, the Very Large Telescope in Chile and the Hobby-Eberly Telescope in
Texas measured the burst's redshift at 0.94. A redshift is a measure of the
distance to an object. A redshift of 0.94 translates into a distance of 7.5
billion light years, meaning the explosion took place 7.5 billion years ago, a
time when the universe was less than half its current age and Earth had yet to
form. This is more than halfway across the visible universe.
"No other
known object or type of explosion could be seen by the naked eye at such an
immense distance," said Swift science team member Stephen Holland of Goddard.
"If someone just happened to be looking at the right place at the right time,
they saw the most distant object ever seen by human eyes without optical
aid."
GRB 080319B's optical afterglow was 2.5 million times more
luminous than the most luminous supernova ever recorded, making it the most
intrinsically bright object ever observed by humans in the universe. The most
distant previous object that could have been seen by the naked eye is the
nearby galaxy M33, a relatively short 2.9 million light-years from
Earth.
Analysis of GRB 080319B is just getting underway, so astronomers
don't know why this burst and its afterglow were so bright. One possibility is
the burst was more energetic than others, perhaps because of the mass, spin, or
magnetic field of the progenitor star or its jet. Or perhaps it concentrated
its energy in a narrow jet that was aimed directly at Earth.
GRB 080319B
was one of four bursts that Swift detected, a Swift record for one day.
"Coincidentally, the passing of Arthur C. Clarke seems to have set the universe
ablaze with gamma ray bursts," said Swift science team member Judith Racusin of
Penn State University in University Park, Pa.
Swift is managed by
Goddard. It was built and is being operated in collaboration with Penn State,
the Los Alamos National Laboratory, and General Dynamics in the U.S.; the
University of Leicester and Mullard Space Sciences Laboratory in the United
Kingdom; Brera Observatory and the Italian Space Agency in Italy; plus partners
in Germany and Japan.
(source: NASA)
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