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The Question

(Submitted May 19, 1997)

Could gamma-ray bursts be due to evaporating mini-black holes as suggested by Stephen Hawking (1974)?

The Answer

This is a very good question, one that gamma-ray astronomers have thought seriously about. They have concluded that evaporating mini-black holes are unlikely to be the origin of (at least the majority of) gamma-ray bursts (GRBs).

Here are some of the reasons:

Every GRB is different: some are complex, some are simple, some are long, some are short, some are hard, some are soft. But every decaying black hole is the same (except for angular momentum and surrounding material).

Decaying black holes have well predicted time and energy behavior. What is expected from a black hole decay is a brief, rapidly hardening flash which would be most observable by Comptel or EGRET. Comptel and EGRET have looked for such, and not found any.

Decaying black holes don't decay unless they are relatively small, so they don't have very much energy, thus they must be in our immediate neighborhood to be seen. In contrast, the distribution of observed GRBs on the sky implies that they are either at cosmological distances or at least rather far out in the Galactic halo.

David Palmer and Koji Mukai
for Ask an Astrophysicist

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