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In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. They occur at random positions in the sky several times each day. As of summer 2003, one of the more promising but still highly speculative ideas is that they are the result of the creation of a black hole from a dying star. The black hole, surrounded by a rotating disk of matter falling into it, somehow emits energetic beams parallel to the axis of rotation.

However, the astrophysical community is still some distance away from coming to a consensus on the mechanism for GRBs, although most are optimistic that the puzzle will be solved by 2010.

1 The Discovery of GRBs

Cosmic gamma-ray bursts were discovered in the late 1960s by the US " Vela" nuclear test detection satellites. The Velas were launched to detect radiation emitted by weapons tests, but they picked up occasional bursts of gamma rays from unknown sources. While the sensors on the Vela satellites had low angular resolution, in 1973 researchers at the US Los Alamos National Laboratory in New Mexico were able to use the data from the satellites to determine that the bursts came from deep space.

Gamma ray bursts can only be observed directly from space, as the atmosphere blocks gamma rays. Astronomers believed that once better gamma-ray detectors were put in orbit, they would be able to quickly pin down the locations of the GRBs. After all, that is what happened with X-ray sources. However, when such improved detectors were sent into space in the 1970s, optical searches of the regions where the bursts originated showed nothing of interest. The sensors were not accurate enough to pinpoint the location of the bursts for detailed study.

Further information on the burst sources proved hard to obtain, and led to more questions than answers. The first question posed by the GRBs was: are they local to our own Galaxy, or do they occur in the distant reaches of the Universe? The second question was: what mechanism causes the bursts? If they do occur in the distant Universe, the mechanism must be producing enormous amounts of energy.

Little progress was made on the matter through the 1980s, but in April 19911991 like 2002, is a palindromic year. It also has the same calendar as 2002, including Easter on March 31. It is a common year starting on Tuesday. Events January January 2 Sharon Pratt Dixon is sworn in as mayor of Washington, DC becoming the first blac, the US National Aeronautics and Space Administration (NASA) launched the " Compton Gamma Ray ObservatoryThe Compton Gamma Ray Observatory CGRO) was the second of the NASA " Great Observatories" to be launched to space, following the Hubble Space Telescope. Compton was: launched on the Space Shuttle Atlantis mission STS-37, on 5 April 1991; de-orbited and en" on board the space shuttle. One of the instruments on board Compton was the "Burst & Transient Source Experiment ( BATSE )", which could detect gamma-ray bursts and locate their positions in the sky with reasonable accuracy. BATSE established that there were at least two categories of gamma ray burst: hard gamma ray burst and soft gamma ray repeaters.

Within a year, BATSE detected two or three GRBs each day, and found that they are randomly distributed over the entire sky. If they were events occurring in our own Galaxy, they would be preferentially distributed in the plane of the Milky WayThe galactic plane is the plane in which the majority of a flattened galaxy's mass lies. The most commonly discussed example is the plane on which the Earth's galaxy, the Milky Way, lies, which is also called the Milky Way's plane or plane of the Milky Wa. Even if they were associated with the galactic haloThe galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. The galactic halo is believed to consist largely of stars, gas and dark matter. Halo stars The bulk of the stars in a spiral galaxy are located either, they would still be preferentially distributed towards the galactic center, 30,000 light yearA light year abbreviated ly is the distance light travels in one year: roughly 9. 46 × 1012 kilometres (9. 46 petametres, or about 5. 88 × 1012 miles). More specifically, a light year is defined as the distance that a photon would travel, in free space ans away, unless the halo were truly enormous. Besides, if that were the case, nearby galaxies would be expected to have similar haloes, but they did not show up as "hot spots" of faint gamma-ray bursts.

To many astronomers, this implied that the GRBs originated in the distant Universe, but that led to the problem of finding a mechanism that could generate so much energy. Other theorists were also still able to come up with "local" models for the GRBs, and BATSE couldn't resolve the issue.

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