Since beginning operation, gravitational-wave observatories have observed several mergers involving neutron stars and black holes. Both black holes and neutron stars are the result of supernovae, so is it possible for us to identify a pair of these objects pre-merger?
An artist’s impression of a black hole–neutron star binary. [Carl Knox, Arc Centre Of Excellence For Gravitational Wave Discovery (Ozgrav) At Swinburne University Of Technology]
Some Go Supernova First
The first black hole–black hole (BH–BH) merger was detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015. Since then, LIGO and the Virgo interferometer have observed several BH–BH and neutron star–neutron star (NS–NS) mergers. Interestingly, the two observatories have also found candidates for BH–NS mergers. So how are the progenitors of these mergers formed?
One possibility is that black holes and neutron stars encounter each other in densely populated areas of space and just happen to pair off. Another possibility is that these pairs of dense objects start off as massive stars in a binary and evolve until they reach their pre-merger form.
Both scenarios involve supernovae, as the stars evolve to become neutron stars or black holes. But there’s an interesting consideration for the latter scenario, if one star ...