Astrophysicists at the LIGO laser interferometric gravitational-wave observatory and the Virgo gravitational wave detector have traced the mergers of neutron stars and black holes for the first time.
We are talking about two gravitational events GW200105 and GW200115. The first is the collision of a black hole with a mass of about nine solar masses and a neutron star with 1.9 solar masses and occurred at a distance of about 900 million light-years from Earth. The second is the merger of a black hole with a mass six times that of a solar and a neutron star with 1.5 times the mass of the Sun – this happened about one billion light-years from Earth.
Further observations of the regions of the sky where these pairs of black holes and neutron stars were supposed to be located indicated that the merger of these objects did not lead to the appearance of visible flashes of light.
Therefore, astronomers concluded that the black holes involved in the merger were large enough to swallow neutron stars entirely, rather than tear them apart.
Gravitational waves allowed us to detect the merging of pairs of black holes and pairs of neutron stars, but the mixed merger of a black hole with a neutron star was an elusive event. This piece of the big picture is crucial for many astrophysical models of the formation of compact objects and the evolution of binary systems.
Chase Kimball, one of the study participants
In theory, a small fraction of this matter might not get past the event horizon, which could result in a flash of light. Since astronomers did not notice such traces, it can be concluded that this happens relatively rarely.