Merger of two neutron stars: predictions from the two-families scenario

TL;DR

This paper compares the outcomes of neutron star mergers under single-family and two-families models, predicting different collapse probabilities that can be tested with gravitational wave observations.

Contribution

It introduces the two-families scenario for neutron stars and predicts distinct merger outcomes, providing a way to differentiate models through gravitational wave data.

Findings

In the single-family scenario, less than 18% of mergers result in immediate black hole formation.

In the two-families scenario, at least 34% of mergers lead to prompt collapse.

The gravitational wave signals from mergers can distinguish between the two scenarios.

Abstract

If only one family of "neutron stars" exists, their maximum mass must be equal or larger than $2 M_\odot$ and then only in less than about $18\%$ of cases the outcome of the merger of two neutron stars is a direct 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 $1.5-1.6 M_\odot$, 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 neutron stars 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.