Scientists believe they have found an explanation for an “impossible” blast of energy that hit Earth.

Last year, scientists reported that they had seen evidence that gamma-ray bursts could come out of mergers between neutron stars and another compact object, in the form of a neutron star or black hole. That was previously thought not to be possible.

Scientists had initially thought that the 50-second blast came when a massive star collapsed, but further work looking at the afterglow of the emission showed that it was in fact a “kilonova”, which happens when neutron stars merge with other compact objects. Previously, it was thought that only a supernova could make a long gamma-ray burst of that kind.