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Observations link gamma-ray bursts to black hole formation

2 October 2001

Over recent years, astronomers have detected numerous short, intense bursts
of gamma rays coming from all over the sky. For a brief instant, these flashes of
radiation are more energetic than anything else in the universe. However, their origin
remains a mystery. New observations of these gamma-ray bursts (GRBs) and their
X-ray afterglow support the theory of electromagnetic black hole formation.

As a giant star collapses into a black hole, an extremely strong
electromagnetic field can form. This energy could accumulate matter and antimatter,
which generate an enormous pulse of energy, expanding with ultrarelativistic
velocities. This produces the observed burst of gamma rays when the expanding
fireball ceases to be opaque.

Using the GRO/BATSE gamma-ray observatory
archive, the Chandra X-ray observatory, the Beppo-Sax satellite and the Rossi-XTE
satellite, a team of Italian and French researchers compared detailed observations of
GRB 991216 with the predictions made by their model. They say that the timing and
intensity of the burst as well as the extended X-ray afterglow can be explained.

The model also explains the association of some GRBs with supernovae
explosions, say the researchers. The impact of the expanding fireball on a nearby star
could, under certain conditions, induce a supernova explosion in that star. Other
GRB theories include the hypernova model ( CERN Courier June).

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