About once a day, a flash of gamma-ray radiation reaches Earth from far out in space. Some of these gamma-ray bursts occur within our own Milky Way galaxy; others occur in galaxies far, far away. Some gamma-ray bursts have been detected more than ten billion light-years away! Gamma rays are the most energetic type of electromagnetic radiation, and stars rarely emit large amounts of them.

Some gamma-ray bursts—especially those within our galaxy—appear to be caused by explosive detonations of some kind in binary star systems. Usually, one or both of the stars in these systems are dense, massive stellar end-products like white dwarfs, neutron stars, or black holes. The gamma-ray bursts observed in distant galaxies could be caused by the collision of neutron stars and/or black holes. Alternately, when a massive star explodes as a supernova just as it is spinning rapidly, the combination of stellar collapse and stellar rotation can emit two super-powerful, tightly focused beams of gamma rays outward into space. These beams are carrying more radiation than the Sun makes in millions, even billions, of years.