August 17, 2017 was a watershed moment for multimessenger astronomy when the gravitational waves and photons from a kilonova were detected for the first time. And GW170817 continues to surprise. A kilonova results from the merger of neutron stars and is thought to be the source of heavy elements such as gold.
Our colleague, Prof. Jon Zrake, was part of team that has monitored the evolution of X-rays from this source. Initially the source was fading, but in 2020 the fading stopped and has remained relatively constant since. This provides intriguing insight to the physics of neutron star mergers and the subsequent explosion. The behavior of the X-rays is somewhat puzzling, and this team has proffered two explanations to account for the behavior – one possibility is that we are seeing the afterglow of the kilonova. Another possibility is that we seeing the accretion signature of material falling into a blackhole formed by the merger of these neutron stars. If the constant brightness is due to an afterglow, we should see the source brighten again. If the result is due to accretion into the black hole, then the source should remain constant or fade away over the next few years. Either result will provide valuable insight to the physics of kilonova. This work was published in the Astrophysical Journal Letters and can be accessed here.
