An international team of astronomers has explained why colliding neutron stars continue to emit X-rays, even though models predict the radiation should have stopped long ago. This is reported in an article published in the Monthly Notices of the Royal Astronomical Society.
The researchers studied the neutron star merger GW170817, which was identified by gravitational waves, as well as a burst of light and gamma radiation on August 17, 2017. Seconds after the gravitational waves were recorded, scientists detected a gamma-ray burst, and then a kilonon, a giant flash formed by an expanding cloud of gas, appeared. The light from the kilonova lasted three weeks and then went out.
However, scientists discovered a mysterious phenomenon: X-rays continued to be emitted for several years after the registration of gravitational waves. Theoretical models predict that when the initial jet from the collision moves through outer space, it creates its own shock wave, emitting X-rays, radio waves and light. This afterglow in the case of GW170817 lasted 160 days and went out, but the X-ray radiation remained.
Researchers have proposed several explanations for the phenomenon at once. For example, X-rays are the result of some unknown mechanism that is not included in the afterglow model. Another possibility is that the kilonova created its own shock wave, which took longer to reach Earth. Finally, after the collision of neutron stars, something remains that continues to emit X-rays.
