Understand
The promise by the LIGO/Virgo/Kagra (LVK) collaboration to detect black hole--neutron star (BH--NS) mergers via gravitational wave (GW) emission has recently been fulfilled with the detection of GW200105 and GW200115.
- Mergers of BH--NS binaries are particularly exciting for their multi-messenger potential, since the GW detection can be followed by an electromagnetic (EM) counterpart (kilonova, gamma-ray burst, afterglow) that can reveal important information on the equation of state (EOS) of NSs and the nature of the BH spin.
- We carry out a statistical study of the binary stars that evolve to form a BH--NS binary and compute the rate of merger events that can be followed by an EM counterpart.
- We find that $\gtrsim 50\%$ of the mergers can lead to an EM counterpart only in the case BHs are born highly spinning ($\chi_{\rm BH}\gtrsim 0.7$), while this fraction does not exceed about $30\%$ for stiff NS EOSs and a few percent for soft NS EOSs for low-spinning BHs ($\chi_{\rm BH}\lesssim 0.2$), suggesting that a high rate of EM counterparts of BH--NS would provide support for high natal BH spins.