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March
21, 2008: A powerful gamma ray burst detected March
19th by NASA's Swift satellite has shattered the record for
the most distant object that could be seen with the naked
eye.
"It
was a whopper," says Swift principal investigator Neil
Gehrels of NASA's Goddard Space Flight Center. "This
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
on March 19, 2008, and pinpointed the coordinates in the constellation
Bootes. Telescopes in space and on the ground quickly moved
to observe the afterglow. The burst was named GRB 080319B
and registered between 5 and 6 on the visual magnitude scale
used by astronomers. (A magnitude 6 star is the dimmest visible
to the human eye; magnitude 5 is almost three times brighter.)
Above:
GRB 080319B makes a brief appearance among the stars of Bootes
in a movie made by Pi of the Sky, a Polish group that monitors
the sky for afterglows and other short-lived phenomena. [More]
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," says 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."
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. When the jets plow into surrounding interstellar
clouds, they heat the gas to incandescent visibility. It is
this gaseous "afterglow" which was visible to the
human eye on March 19th.
GRB
080319B's 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.
 Right:
The afterglow of GRB 080319B as recorded by Swift's X-ray
Telescope. [More]
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 on
March 19th, a Swift record for one day. Swift science team
member Judith Racusin of Penn State University comments, "coincidentally,
the passing of Arthur C. Clarke seems to have set the universe
ablaze with gamma ray bursts." A fitting farewell, indeed.
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Editor: Dr.
Tony Phillips | Credit: Science@NASA
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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
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