A powerful
stellar explosion that has shattered the record for the most distant object
visible to the naked eye was detected by NASA's Swift satellite on Wednesday.
The
explosion, known as a gamma-ray
burst, also ranks as the most intrinsically bright object in the universe
ever observed by humans.
"It's
amazing — we've been waiting for a flash this bright from a gamma-ray burst
ever since Swift began observing the sky three years ago, and now we've got one
that is so bright that it was visible to the naked eye even though its source
is half-way across the universe," said David Burrows of Penn State
University, who directs the continuing operation of Swift's X-ray telescope and
the analysis of the data it collects.
Gamma-ray
bursts are the most luminous explosions in the universe since the Big
Bang and occur when massive stars run out of nuclear fuel. The stars' cores
collapse to form black holes or neutron stars and release an intense burst of
high-energy gamma-rays and jets of energetic particles.
The jets
rip through space at nearly the speed of light, heating the surrounding
interstellar gas like turbocharged cosmic blowtorches, often generating a
bright afterglow.
"These
optical flashes from gamma-ray bursts are the most extreme such phenomena that
we know of," said Swift science team member Derek Fox, also of Penn State. "If this burst had happened in our galaxy, it would have been shining
brighter than the Sun for almost a minute — sunglasses would definitely be
advised."
Penn State astronomer and Swift
team member Peter Meszaros said an unusual combination of circumstances may
have made the burst's afterglow so exceptionally bright in the visible
wavelengths of light.
"When
the jet that formed during the explosion of the star slammed into the
surrounding gas clouds, shock waves were generated that heated the jet,"
he explained. "The exceptional brightness of this burst requires the jet
to have just the right combination of magnetic fields and velocity, which
occurs very rarely."
Astronomers
don't know for sure what made the burst, dubbed GRB 080319B, so bright, but
further analysis of the event is under way. The burst could possibly have been
more energetic than others, or the burst's energy may have been concentrated in
a jet aimed directly at Earth.
The
afterglow of GRB 080319B was 2.5 million times more luminous than the most
luminous supernova ever recorded, making it the most intrinsically bright
object ever recorded.
Astronomers
have placed the star in the constellation Boötes. They have estimated it to be
7.5 billion light years away from Earth, meaning the explosion took place when
the universe was less than half its current age and before Earth formed.
The most
distant previous object that could be seen by the naked eye is the galaxy M33,
a relatively short 2.9 million light-years from Earth.
The burst
was detected by Swift at 2:12 EDT on March 19 and was one of five gamma-ray
bursts detected that day, the same day that famed science fiction writer Arthur C.
Clarke died.
"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, a Penn State graduate student.
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