Astronomers think gamma-ray bursts may be linked to black holes but aren't sure of the exact circumstances of their creation. One idea is that gamma-ray bursts are produced after a massive star explodes and leaves a black hole in its place. Another idea is that they're produced when two neutron stars collide to form a black hole. The appearance of a gamma-ray burst is unpredictable, but one appears about once per day.
ESA / ECF