Cosmic explosions: detecting the highest-energy light

The most energetic form of light has been detected from a distant but powerful cosmic explosion known as a 'gamma-ray burst' for the first time, by an international team including UCL physicists using a UCL-built space telescope onboard NASA's Neil Gehrels Swift Observatory. The discovery and in particular, the unknown mechanisms that cause extremely high-energy light to be emitted in the afterglow of a gamma-ray burst (GRB). Study co-author, Dr Paul Kuin (UCL Mullard Space Science Laboratory, UCL Space & Climate Physics), said: "Since launching in 2004, Swift has greatly increased our understanding of gamma-ray bursts which occur almost daily in the sky and are characterised by brief, but intense, flashes followed by an afterglow which fades over time. We've now seen that extremely high-energy light is released in the afterglow period - something that was only predicted before in models - and comparative studies suggest that this is not an unusual feature." GRBs are the most violent explosions in the Universe since the Big Bang and are thought to follow the collapse of massive stars or the merging of neutron stars or black holes in distant galaxies. In only a few seconds, these events release an energy comparable to that emitted by our Sun during its whole life, blasting jets of particles outward at nearly the speed of light. They produce an initial pulse of gamma rays - the most energetic form of light - that typically lasts about a minute. As the jets race outward, they interact with surrounding gas and emit light across the spectrum, from radio to gamma rays.