Comprehensive survey of hybrid equations of state in neutron star mergers and constraints on the hadron-quark phase transition

TL;DR

This comprehensive survey analyzes how different hadron-quark phase transition models in neutron star mergers influence gravitational-wave signals, aiming to constrain the properties of such phase transitions through simulation results.

Contribution

It systematically explores a wide range of hybrid EoS models to identify gravitational-wave signatures indicative of phase transitions in neutron star mergers.

Findings

Density jump at transition significantly affects GW frequencies.

Quark matter stiffness has a smaller impact on GW signals.

Certain phase transition properties can be constrained by future GW detections.

Abstract

We perform an extensive study of equation of state (EoS) models featuring a phase transition from hadronic to deconfined quark matter in neutron star merger simulations. We employ three different hadronic EoSs, a constant speed of sound parameterization for the quark phase and a Maxwell construction to generate a large sample of hybrid EoS models. We systematically vary the onset density and density jump of the phase transition as well as the quark matter stiffness and simulate binary neutron star mergers to infer how the properties of the phase transition affect the gravitational-wave signal. In total we simulate mergers with 245 different hybrid EoS models. In particular, we explore in which scenarios a phase transition would be detectable by a characteristically increased postmerger gravitational-wave frequency compared to an estimate from the inspiral signal assuming a purely hadronic EoS. We find that the density jump at the transition (latent heat) has the largest impact on the gravitational-wave frequencies, while the influence of the stiffness of quark matter is smaller. We quantify which range of phase transition properties would be compatible with a certain magnitude or absence of the gravitational-wave postmerger frequency shift. By means of these dependencies, a future detection will thus directly yield constraints on the allowed features of the hadron-quark phase transition.