Back in February, scientists from the Laser Interferometer Gravitational Wave Observatory (LIGO) announced they had finally detected gravitational waves, ripples in space-time caused by a black hole merger that confirmed one of the last predictions of Einstein's theory of general relativity. Now, NASA claims that it has detected a gamma-ray burst near the vicinity of the source of these waves, shedding light on the mysterious black hole merger and calling our knowledge of these events into question.
The brief, weak burst of X-rays was discovered by NASA's Fermi Gamma-ray Space Telescope and is consistent with the characteristics of a short gamma-ray burst (GRB). Furthermore, the burst was detected less than half a second after the LIGO picked up the first gravitational waves, an event dubbed GW150914.
The findings are surprising because researchers previously thought that black hole collisions were "clean," with no electromagnetic traces left behind. If the gamma-ray burst stems from the same event as GW150914, which looks to be the case, then it will alter our current perception of black hole mergers.
"This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks, we'll need to see more bursts associated with gravitational waves from black hole mergers," said Valerie Connaughton, a member of the Gamma-ray Burst Monitor (GBM) team at the National Space, Science and Technology Center in Huntsville, Ala.
GRBs are believed to stem from the implosion of massive stars after they run out of fuel, leading to the formation of black holes. However, these gamma rays are known as "long GRBs," contrary to the current signal that looks to belong to the more mysterious class of "short GRBs," which possess a period of less than two seconds.
"With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB," said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "There is an incredible synergy between the two observations, with gamma rays revealing details about the source's energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event."
Black hole mergers aren't thought to create much electromagnetic energy unless there is a source of gas nearby, which doesn't look to be the case for the collision that led to GW150914. Future research should focus on determining if this faint GRB is actually connected to the merger that created the first detected gravitational waves and if we need to rethink our current understanding of black hole dynamics.
