Artist’s visualization of a merging binary system: Shorter Gamma-Ray Bursts (less than two seconds in duration) are believed to be separate phenomena from longer GRBs. They are thought to be caused by mergers of binary systems with black holes or neutron stars.
Credit: NASA/Dana Berry, Skyworks Digital
We know a little more, yes. But there are still questions about the origins of GRBs. At the present time, there are two prevalent theories explaining the origin of gamma-ray bursts: the merging of two neutron stars and a collapsar/hypernova. The first has been associated with short bursts, while the latter with their longer brethren (those with more than about 2 seconds duration). The truth, however, may lie somewhere between these two theories -- for example, short bursts may be collapsar/hypernovae, or a different model can be employed to explain some of the events. The bottom line is that there are way too many members in the GRB club, and there is no a priori reason why they can all be explained by the same origin. It may well be that GRBs originate from something that astronomers haven't considered yet. We're still waiting to see more to be sure. If a short GRB is due to merging neutron stars, then it should produce powerful bursts of gravitational radiation. Although Albert Einstein included gravitational waves in his 1916 General Theory of Relativity, these waves have never been measured directly. Short GRBs, apparently 10 times closer to Earth than long GRBs, likely emit gravitational waves that will be detectable for the first time by future instruments, such as the Advanced-LIGO (Laser Interferometer Gravitational-Wave Observatory).