Signals in the tidal deformability for phase transitions in compact stars with constraints from GW170817

TL;DR

This paper investigates how phase transitions in neutron stars affect their tidal deformabilities during mergers, suggesting future gravitational wave observations could reveal evidence of such phase transitions.

Contribution

It introduces a method to identify strong first order phase transitions in neutron star matter through analysis of tidal deformability data from mergers.

Findings

Up to three separate branches in the $\Lambda_1$-$\Lambda_2$ plane can occur.

All three pairs of neutron star branches can be present at a total mass of 2.7 solar masses.

Future detections with the same $\Lambda_1$ but different $\Lambda_2$ can signal phase transitions.

Abstract

We compute the tidal deformabilities for neutron star merger for equations of state with a strong first order phase transition producing a new separate branch in the mass-radius diagram. A case is found where all three possible pairs of combinations between these two neutron star branches are present for the total mass of $M=2.7M_\odot$ of the observed merger event GW170817. It is demonstrated that the plot of the two tidal deformabilities $\Lambda_1$ and $\Lambda_2$ of the binary neutron star can show up to three separate branches. We propose that the future detections of neutron star merger events with the same value for $\Lambda_1$ but different values of $\Lambda_2$ serve as a signal for the existence of a strong first order phase transition in neutron star matter.