Merger of Two Neutron Stars: Predictions from the Two-families Scenario

If only one family of "neutron stars" exists, their maximum mass must be equal to or larger than $2M_{\odot }$ and then, only in less than about 18% of cases, the outcome of the merger of two neutron stars is a prompt collapse to a black hole, since the newly formed system can avoid the collapse at least until differential rotation is present. In the so-called two-families scenario, stars made of hadrons are stable only up to about $\left(1.5\text{--}1.6\right)M_{\odot }$, while the most massive compact stars are entirely made of strange quark matter. We show that in this scenario the outcome of the merger of two compact stars, entirely composed by hadrons, is a prompt collapse in at least 34% of the cases. It will therefore be easy to discriminate between the two scenarios once the gravitational waves emitted at the moment of the merger are detected. Finally, we shortly discuss the implications of GW170817−GRB 170817A.