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April
28, 2009: NASA's Swift satellite and an international
team of astronomers have found a gamma-ray burst from a star
that died when the universe was only 630 million years old--less
than five percent of its present age. The event, dubbed GRB
090423, is the most distant cosmic explosion ever seen.
"The
incredible distance to this burst exceeded our greatest expectations
-- it was a true blast from the past," says Swift lead
scientist Neil Gehrels at NASA's Goddard Space Flight Center.
Above:
GRB 090423 as seen by NASA's Swift satellite. The image is
a composite of data from Swift's UV/Optical and X-Ray telescopes.
Credit: NASA/Swift/Stefan Immler [Larger
image]
The
burst occurred at 3:55 a.m. EDT on April 23rd. Swift quickly
pinpointed the explosion, allowing telescopes on Earth to
target the burst before its afterglow faded away. Astronomers
working in Chile and the Canary Islands independently measured
the explosion's redshift.
It was 8.2, smashing the previous record of 6.7 set by an
explosion in September 2008. A redshift of 8.2 corresponds
to a distance of 13.035 billion light years.
"We're
seeing the demise of a star -- and probably the birth of a
black hole -- in one of the universe's earliest stellar generations,"
says Derek Fox at Pennsylvania State University.
Gamma-ray
bursts are the most luminous explosions in the Universe. Most
occur when massive stars run out of nuclear fuel. As their
cores collapse into a black hole or neutron star, jets of
matter punch through the star and blast into space. There,
they strike gas previously shed by the star and heat it, which
generates short-lived afterglows in many wavelengths.
For
years, astronomers have been hunting for gamma-ray bursts
from the earliest generations of stars--and mysteriously failing
to find them. The detection of GRB 090423 is an important
milestone in the quest to locate bursts in the redshift range
10 to 20. More information: "The
Case of the Missing Gamma-ray Bursts."
Within
three hours of the April 23rd burst, Nial Tanvir at the University
of Leicester, U.K., and his colleagues reported detection
of an infrared source at the Swift position using the United
Kingdom Infrared Telescope on Mauna Kea, Hawaii.
 At
the same time, Fox led an effort to obtain infrared images
of the afterglow using the Gemini North Telescope on Mauna
Kea. The source appeared in longer-wavelength images but was
absent in an image taken at the shortest wavelength of 1 micron.
This "drop out" corresponded to a distance of about
13 billion light-years.
Right:
An artist's concept of a gamma-ray burst in action. Click
on the image for animations.
Credit: NASA/Swift/Cruz deWilde.
As
Fox spread the word about the record distance, telescopes
around the world turned to observe the afterglow before it
faded away.
At
the Galileo National Telescope on La Palma in the Canary Islands,
a team including Guido Chincarini at the University of Milan-Bicocca,
Italy, determined that the afterglow's redshift was 8.2. Tanvir's
team, gathering nearly simultaneous observations using one
of the European Southern Observatory's Very Large Telescopes
on Cerro Paranal, Chile, arrived at the same number.
"It's
an incredible find," Chincarini says. "What makes
it even better is that a telescope named for Galileo made
this measurement during the year in which we celebrate the
400th anniversary of Galileo's first astronomical use of the
telescope."
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Editor: Dr.
Tony Phillips | Credit: Science@NASA
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information |
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home page: Swift
Credits:
NASA's Goddard Space Flight Center manages Swift. It
was built and is being operated in collaboration with
Pennsylvania State University, the Los Alamos National
Laboratory in New Mexico, and General Dynamics of Gilbert,
Ariz., in the United States. International collaborators
include the University of Leicester and Mullard Space
Sciences Laboratory in the United Kingdom, Brera Observatory
and the Italian Space Agency in Italy, and additional
partners in Germany and Japan.
NASA's
Future: US
Space Exploration Policy |
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