Probing the universe with gamma-ray bursts

The long-soft class of GRBs is believed to be produced during the final stages of the evolution of some massive stars, when an accretion disk forms around a new black hole and enormous energy releases in the vicinity of the black hole drive ultra-relativistic jets through the star along its rotation axis. The short-hard class of GRBs is also believed to be associated with a black hole - accretion disk -jet system, but with merging binary systems of compact stars (e.g., a neutron star binary) as progenitors. Both of these source classes trace, more or less directly, the cosmic star formation history, and thus offer a unique probe of the high redshift Universe. Regardless of the nature of their central engines, and their progenitors, their high luminosities allow easy detection even at very large distances, and their optical afterglows provide a (rapidly decaying) light source that offers unique opportunities for spectroscopic studies of interstellar gas in the evolving Universe.