Symmetry energy effect on the secondary component of GW190814 as a neutron star

TL;DR

This study investigates how the symmetry energy influences the equation of state of neutron star matter, assessing if the secondary of GW190814 could be a massive neutron star supported by specific nuclear physics constraints.

Contribution

It introduces a density-dependent relativistic mean-field model to explore the symmetry energy's role in supporting massive neutron stars like the secondary of GW190814.

Findings

Symmetry energy slope L ≤ 50 MeV supports a 2.6 M_sun neutron star

Constraints from tidal deformability are compatible with a neutron star origin

Massive neutron star possibility remains viable under current EOS constraints

Abstract

The secondary component of GW190814 with a mass of 2.50-2.67 $M_{\odot}$ may be the lightest black hole or the heaviest neutron star ever observed in a binary compact object system. To explore the possible equation of state (EOS), which can support such massive neutron star, we apply the relativistic mean-field model with a density-dependent isovector coupling constant to describe the neutron-star matter. The acceptable EOS should satisfy some constraints: the EOS model can provide a satisfactory description of the nuclei; the maximum mass $M_\textrm{TOV}$ is above 2.6 $M_{\odot}$; the tidal deformability of a canonical 1.4 $M_{\odot}$ neutron star $\Lambda_{1.4}$ should lie in the constrained range from GW170817. In this paper, we find that the nuclear symmetry energy and its density dependence play a crucial role in determining the EOS of neutron-star matter. The constraints from the mass of 2.6 $M_{\odot}$ and the tidal deformability $\Lambda_{1.4}=616_{-158}^{+273}$ (based on the assumption that GW190814 is a neutron star-black hole binary) can be satisfied as the slope of symmetry energy $L \leq 50$ MeV. Even including the constraint of $\Lambda_{1.4}=190_{-120}^{+390}$ from GW170817 which suppresses the EOS stiffness at low density, the possibility that the secondary component of GW190814 is a massive neutron star cannot be excluded in this study.