Illustration of a gamma-ray burst (GRB, white jet) during the collapse of a massive star. Gamma-ray bursts are extremely high-energy events. The burst is a flash of radiation which may be as bright as the rest of the universe combined for a few seconds. Most observed GRBs are thought to be generated during a supernova, or superluminous supernova, as a high-mass star collapses to form a neutron star or, as here, a black hole.