Illustration of a long gamma-ray burst (GRB). GRBs are high energy explosions that can either be long burst, lasting two seconds or more, or short burst, lasting less than two seconds. This GRB has formed from the collapse of a massive star into a black hole (black dot, centre). Some of the matter accelerating towards a black hole is emitted as jets of high-speed particles, drilling through the star and producing gamma-rays when they emerge. GRBs can only be detected if one of these jets is pointed towards Earth.