Studying VLOCV twin compact stars with binary mergers

TL;DR

This study models twin compact stars with phase transitions using VLOCV equations of state, constrained by gravitational wave and NICER observations, revealing conditions for the existence of twin star configurations.

Contribution

It introduces a VLOCV-based EoS with phase transition considerations that predict twin star configurations consistent with recent astrophysical observations.

Findings

VLOCV EoS predicts stiff neutron star matter requiring phase transition.

Twin star configurations are possible with specific transition pressures.

Models align with constraints from GW and NICER data.

Abstract

GW170817 has provided valuable constraints on the equations of state of merging binary neutron stars, which can be considered as the most probable candidate for the source of gravitational waves. On the other hand, these natural laboratories of extreme temperature and density may lead to the estimation of some exotic matter like {deconfined quark matter in their cores}. In this paper, we investigate the neutron star matter equation of state (EoS) with the lowest order constrained variational (LOCV) method considering the excluded volume effect (VLOCV) for nucleons {to} compute the tidal deformability of binary neutron star mergers (BNSMs). Within this approach, the size of nucleons makes the EoS {so} stiff that requires a phase transition in order to avoid causality violation. Therefore, this phase transition {may lead} to the appearance of the third family of compact stars {including} ``twin star'' configurations. {Our EoS models are confronted with observations from GW170817, GW190814, GW190425, and also NICER. We find out that regarding all these constraints, the EoS models having the {transition} pressure$\approx$30-100 MeV/fm$^{3}$ and the energy density discontinuity $\Delta\varepsilon$$\lesssim$300 MeV/fm$^{3}$ are preferable.