Astrophysics

One Pulse Leads to Another

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Science  27 Jul 2001:
Vol. 293, Issue 5530, pp. 575
DOI: 10.1126/science.293.5530.575a

A gamma ray burst (GRB) is an extremely energetic and short-lived fireball, whose origin is not understood. In a series of three papers, Ruffini et al. describe a new model for GRB formation based on an electromagnetic black hole. They propose that a massive star collapses because of gravity and forms a black hole with a strong electric field. Electron and positron pairs are created in the condensing material, and these pairs collide, releasing a pulse of plasma outward. This pulse expands at nearly the speed of light and collides with the baryonic matter left over from the progenitor star, creating a second pulse containing electron and positron pairs as well as photons, baryons, and electrons. Eventually, the density of the material in the pulse reaches a level where the gamma ray radiation can be detected by dobservers.

The baryonic matter continues to accelerate outward, reaching ultrarelativistic speeds, into the interstellar medium, and a high-speed collision with any structure in the interstellar medium would then create an afterglow. If a second star is lurking near the electromagnetic black hole, the accelerated baryonic matter would trigger a supernova upon collision.

Thus, this model, without positing unusual physical properties of the progenitor, can account for many of the recent observations of GRBs, particularly their afterglows and the correlation with some supernovae. If GRBs do form from electromagnetic black holes, then astronomers will be able to use GRBs as standard candles to estimate cosmic distances and probe the properties of the early universe. — LR

Astrophys. J.555, L107; L113; L117 (2001).

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