ESA Science & Technology30-Jun-2005 16:32:26

Background Science

Cosmic Gamma-Ray Bursts

Cosmic gamma-ray bursts are the most powerful explosions in the known universe. They appear to be generated by the collapse of very massive stars (~100 solar masses). The distances to about a dozen sources have now been measured, showing that they are at cosmological distances comparable to those of quasars. If the bursts emit their energy uniformly into space, their output is 1053 erg in gamma-rays alone. In addition to being interesting in their own right, gamma-ray bursts are being used by cosmologists as probes of the early universe.

Hubble Space
Telescope image of
the galaxy where the
gamma-ray burst of
March 1 2000
originated. This burst
came from a distance
of 11 billion light-years.
Ulysses and the Rossi
X-Ray Timing Explorer
determined its position.


The following instrument measures cosmic gamma-ray bursts on board Ulysses:
GRB (Gamma-Ray Burst detector)

GRB (Gamma-Ray Burst detector)
GRB is a key member of the 3rd Interplanetary Network (IPN) of gamma-ray burst detectors, which locates bursts precisely by comparing their arrival times at widely separated spacecraft. In the course of studying gamma-ray bursts, GRB has played a major role in the study of so-called soft gamma repeaters, or 'magnetars'.

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