But a team including Zhang has a suggestion for what might have caused it: the merger of a neutron star not with another neutron star, as is common for short gamma ray bursts, but with a white dwarf. White dwarfs are larger than neutron stars, but not nearly as big as the massive stars that cause supernovae, which would account for the length and intensity of the unusual burst.
Since there are lots of white dwarf-neutron star binaries and events like this are rare enough that it’s the first to be observed in half a century of looking, he suggests it needs some qualifications: first, the white dwarf needs to be “close to the upper mass limit,” and afterwards the two need to merge into a rapidly-spinning magnetar, which would “inject additional energy into the kilonova.”
