Studying VLOCV twin compact stars with binary mergers

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≈30-100 MeV/fm 3 and the energy density discontinuity ∆ε < ∼ 300 MeV/fm 3 are preferable.