Astronomers Detect Most Powerful Explosion Since Big Bang
The energy released in a cosmic gamma-ray burst detected in
December 1997 is the most energy ever detected from an explosion in the
Universe, perhaps 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 burst was detected on Dec. 14, 1997, by the
Italian/Dutch BeppoSAX satellite
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
"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, which until now
was 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
milli second (1/1,000 of a second) after the Big Bang," said
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 durations exacerbate 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
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 Milky Way Galaxy, but rather are associated with
extremely distant galaxies. The faint galaxy from which
GRB 971214 originated is estimated to be about 12 billion light years
from the Earth. The galaxy is about as faint as an ordinary 100 watt light
bulb would be as seen from a distance of a million miles.
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.
The cause of the observed explosion is unknown. Scientists have several
models, such as a neutron star falling into a black hole (see the movie
below) or two black holes
colliding, which may account for such an explosion. However, only
future, better observations will permit researchers to choose among competing
theories for the origin of gamma-ray bursts.