Astronomers might have found evidence for a violent stellar merger that can potentially explain one of the most energetic events in the universe: gamma-ray bursts.
Gamma-ray bursts (GRBs) – the brightest events in the cosmos – are sudden and quick flashes of gamma-ray light from very distant galaxies. One of these GRBs was detected by NASA’s Swift observatory on September 3, 2014, and the analysis of this event has now been released.
It lasted for less than two seconds and released 2x1043 joules of energy, which is about 15 percent of the lifetime energy output of the Sun. The brevity of this GRB suggests that it was caused by a collision of either neutron stars or a neutron star and a black hole.
Such an event requires special attention, and researchers quickly followed up the first detection with several other instruments, trying to identify the cause of the GRB.
The observation with Chandra, NASA’s X-ray telescope, delivered the most interesting information regarding the event. For 21 days, the source was monitored and the way the emission decreased over time provided important information on the source. Their findings are reported in the Astrophysical Journal and they can be read online at arXiv.
The GRB is located in a galaxy 3.9 billion light-years away. The afterglow indicated that the collision produced a narrow jet of gamma rays, which astronomers were only able to detect because it was pointing right at Earth. This implies that only 0.4 percent of these GRBs can be detected.
But that doesn’t mean that there are no other ways to observe neutron star collisions. Mergers between either two neutron stars or a neutron star and black hole are expected to produce a large number of gravitational waves, so LIGO could observe these events without the need to see a GRB first.
Soon, gravitational wave observatories will be capable of pinpointing the precise location in the sky of an event, and when that happens, GRBs will finally reveal their secrets.