Gamma-ray bursts, whivh can release as much energy in a few minutes as the Sun emits in its 10-billion-year lifetime, are among the most mysterious phenomena in the universe. They are the most powerful explosions the Universe has seen since the Big Bang. They come from all different directions of the sky and last from a few milliseconds to a few hundred seconds. They occur approximately once per day and are brief, but intense, flashes of gamma radiation. Yet what causes these mighty blasts is still unknown.
Gamma-ray bursts were first observed during the Cold War. In the late 1960s, US military satellites designed to look for clandestine nuclear tests picked up powerful bursts of radiation. Some even thought that they might be the product of Soviet nuclear tests on the Moon or on other planets. In fact, they came from deep space.
Scientists think that gamma-ray bursts are generated in two principal scenarios. In one scenario, a star collapses in on itself, giving birth to a black hole. Scientists also think the bursts can form when two neutron stars collide.
Some speculated that gamma-ray bursts could even be implicated in some extinctions in Earth history: Even if a gamma-ray burst went off in the centre of our galaxy, which is 30,000 light years away, it would still rival the Sun in terms of brightness.
As technology improved, astronomers were able to react more swiftly to these fleeting events and turn their telescopes towards them while they lasted, where they sometimes detected a fading optical glow from the same strange object.
On October 2000 four spacecrafts have detected the afterglow of the most distant gamma-ray burst ever recorded. They have revealed that the burst probably came from a gigantic dying star more than 30 times the mass of the Sun and which exploded when the Universe was about one tenth of its present age. The spacecrafts that detected this burst were the Ulysses spacecraft, the Near Earth Asteroid Rendezvous (Near-Shoemaker) craft, the Wind spacecraft, and the Italian Bepposax spacecraft.
The latest breakthrough began on March 2004 when the High-Energy Transient Explorer satellite (Hete) detected one of the brightest and closest gamma-ray bursts ever seen.
Located in the constellation of Leo, the 30-second burst, designated GRB 030329, outshone the entire Universe in gamma rays. Its optical afterglow was still over a trillion times brighter than the Sun over two hours later.
Currently, astronomers see about one or two gamma-ray bursts each month. But it is hoped that after the launch of a space probe called Swift, this could go up to about 100 bursts observed per year.
Swift, The $250m NASA probe with international cooperations, could lift off on 8 November 2004 at the earliest. Swift will orbit Earth in wait for a gamma-ray burst. Within about 20 seconds of a detection, Swift relays the position of the burst to the ground. As it relays this information, the spacecraft veers around to train its two onboard telescopes on the source, enabling precision measurements to be made. The spacecraft gets its name from the speed with which it has to move in order to observe the short-lived phenomena.
During its 2-year mission, Swift is expected to observe more than 200 gamma-ray bursts.