THE FOLLOWING RELEASE WAS RECEIVED FROM NASA HEADQUARTERS, IN WASHINGTON,
DC, AND IS FORWARDED FOR YOUR INFORMATION. NOTE THAT DATA ON IMAGE
AVAILABILITY ARE GIVEN AT THE END. Steve Maran, American Astronomical
EMBARGOED UNTIL 2:00 P.M. EDT, MAY 6, 1998
Headquarters, Washington, DC
Goddard Space Flight Center, Greenbelt, MD
California Institute of Technology, Pasadena, CA
MOST POWERFUL EXPLOSION SINCE THE BIG BANG
CHALLENGES GAMMA RAY BURST THEORIES
A recently detected cosmic gamma ray burst released a
hundred times more energy than previously theorized, making it the most
powerful explosion since the creation of the universe in the Big Bang.
"For about one or two seconds, this burst was as luminous as all
the rest of the entire universe," said Caltech professor George
Djorgovski, one of the two principal investigators on the team from the
California Institute of Technology, Pasadena, CA.
The team measured the distance to a faint galaxy from which the
burst originated at about 12 billion light years from the Earth. The
observed brightness of the burst despite this great distance implies an
enormous energy release. The team's findings appear in the May 7 issue
of the journal Nature.
The burst was detected on Dec. 14, 1997, by the Italian/Dutch
BeppoSAX satellite and NASA's Compton Gamma Ray Observatory satellite.
The Compton observatory provided detailed measurements of the total
brightness of the burst, designated GRB 971214, while BeppoSAX provided
its precise location, enabling follow-up observations with
ground-based telescopes and NASA's Hubble Space Telescope.
"The energy released by this burst in its first few seconds
staggers the imagination," said Caltech professor Shrinivas Kulkarni,
the other principal investigator on the team.
The burst appears to have released several hundred times more
energy than an exploding star, called a supernova, until now the most
energetic known phenomenon in the universe. Finding such a large
energy release over such a brief period of time is unprecedented in
astronomy, except for the Big Bang itself.
"In a region about a hundred miles across, the burst created
conditions like those in the early universe, about one millisecond
(1/1,000 of a second) after the Big Bang," said Djorgovski.
This large amount of energy was a surprise to astronomers.
"Most of the theoretical models proposed to explain these bursts cannot
explain this much energy," said Kulkarni. "However, there are recent
models, involving rotating black holes, which can work. On the other
hand, this is such an extreme phenomenon that it is possible we are
dealing with something completely unanticipated and even more exotic."
Gamma-ray bursts are mysterious flashes of high-energy radiation
that appear from random directions in space and typically last a few
seconds. They were first discovered by U.S. Air Force Vela satellites
in the 1960s. Since then, numerous theories of their origin have been
proposed, but the causes of gamma-ray bursts remain unknown. The
Compton observatory has detected several thousand bursts so far.
The principal limitation in understanding the bursts was the
difficulty in pinpointing their direction on the sky. Unlike visible
light, gamma rays are exceedingly difficult to observe with a
telescope, and the bursts' short duration exacerbates the problem.
With BeppoSAX, scientists now have a tool to localize the bursts on the
celestial sphere with sufficient precision to permit follow-up
observations with the world's most powerful ground-based telescopes.
This breakthrough led to the discovery of long-lived
"afterglows" of bursts in X-rays, visible and infrared light, and radio
waves. While gamma-ray bursts last only a few seconds, their
afterglows can be studied for several months. Study of the afterglows
indicated that the bursts do not originate within our own galaxy, the
Milky Way, but rather are associated with extremely distant galaxies.
Both BeppoSAX and NASA's Rossi X-ray Timing Explorer spacecraft
detected an X-ray afterglow. BeppoSAX precision led to the detection
of a visible light afterglow, found by a team from Columbia University,
New York, NY, and Dartmouth College, Hanover, NH, including Professors
Jules Halpern, David Helfand, John Torstensen, and their collaborators,
using a 2.4-meter telescope at Kitt Peak, AZ, but no distance could be
measured from these observations.
As the visible light from the burst afterglow faded, the Caltech
team detected an extremely faint galaxy at its location, using one of
the world's largest telescopes, the 10-meter Keck II telescope at Mauna
Kea, Hawaii. The galaxy is about as faint as an ordinary 100 watt
light bulb would be as seen from a distance of a million miles.
Subsequent images taken with the Hubble Space Telescope
confirmed the association of the burst afterglow with this faint galaxy
and provided a more detailed image of the host galaxy.
The Caltech team succeeded in measuring the distance to this
galaxy, using the light-gathering power of the Keck II telescope. The
galaxy is at a redshift of z=3.4, or about 12 billion light years
distant (assuming the universe to be about 14 billion years old).
From the distance and the observed brightness of the burst,
astronomers derived the amount of energy released in the flash.
Although the burst lasted approximately 50 seconds, the energy released
was hundreds of times larger than the energy given out in supernova
explosions, and it is about equal to the amount of energy radiated by
our entire Galaxy over a period of a couple of centuries. Scientists
say it is possible that other forms of radiation from the burst, such
as neutrinos or gravity waves, which are extremely difficult to detect,
carried a hundred times more energy than that.
NASA is planning two missions to further investigate gamma-ray
bursts: the High Energy Transient Experiment II (HETE II), scheduled
to launch in the fall of 1999, and the Gamma Ray Large Area Space
Telescope (GLAST), scheduled to launch in 2005. HETE II will be able
to precisely locate gamma-ray bursts in near real-time and quickly
transmit their locations to ground-based observatories, permitting
rapid follow-up studies. GLAST will detect only those gamma-ray bursts
that emit the highest energy gamma rays, and will be able to locate
them with sufficient precision to permit coordinated observations from
the ground. Because not much is known about the bursts at these high
energies, the observations may permit researchers to choose among
competing theories for the origin of gamma-ray bursts.
NOTE TO EDITORS: Images of the GRB 971214 field are available at:
Information on the BeppoSAX spacecraft is available at:
Information on the Compton Gamma Ray Observatory is available at:
Information on Gamma Ray Bursts is available at:
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