We still do not know for certain what these gamma ray bursts are caused by, but astronomers are learning more about them each year as the evidence continues to mount. As of the final end of mission count, the NASA Gamma Ray Observatory called BATSE has now seen 2704 of them from all over the sky.
There are still two camps of astronomers who describe them either as 'local phenomena related to some unknown class of objects in the halo of the Milky Way galaxy', or that they are 'cosmological' phenomena produced by objects over a billion light years from the earth'. Because a number of these bursts have now been tracked to distant galaxies, it is now becoming clearer that they are produced by cosmologically very distant galaxies. I haven't heard any other 'local arguments' so I think that that entire discussion has now ended. The bursts can be grouped into bright and faint ones, and the distribution of the energy from the pulses shows that there is a distinct shift between the two groups of the kind you would expect if the faint group were statistically farther away in the universe than the bright ones. Both groups are at billions of light years distance.
Because the bursts last less than a second, one popular mechanism involves the collision of two neutron stars in a binary system. The binary system continued to shrink in size due to the loss of gravitational energy until the two stars came within their mutual tidal influences and literally tore each other apart. The only problem is that this is believed to be a messy process that would last longer than a few minutes -- a typical orbital time, and leave behind lots of hot matter capable of being observed via its X-ray signature. Gamma ray bursts, however, leave behind very little X-ray energy after the burst so this doesn't seem to add up.
Neutron stars can also collide with black holes, and this could also produce a brilliant pulse of energy.
At the present time, enough bursts have now been detected to all but rule out the possibility that they originate in the vast halo of our Milky, and strengthens the argument that they are 'cosmological'. One possibility is that they are produced in very distant galaxies by the black hole - neutron star collision scenario. Because there isn't much of a range in brightness for these pulses, they are believed to come from a rather limited range of distances; similar to a large sphere of space with a rather distinct outer boundary. It is very peculiar to say the least!
Copyright 1997 Dr. Sten Odenwald
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