Effect of the symmetry energy on the secondary component of GW190814 as a neutron star
Xuhao Wu, Shishao Bao, Hong Shen, Renxin Xu
Abstract
The secondary component of GW190814 with a mass of 2.50--2.67 ${M}_{\ensuremath{\bigodot}}$ 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 a 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 ${M}_{\text{TOV}}$ is above 2.6 ${M}_{\ensuremath{\bigodot}}$; the tidal deformability of a canonical 1.4 ${M}_{\ensuremath{\bigodot}}$ neutron star ${\mathrm{\ensuremath{\Lambda}}}_{1.4}$ should lie in the constrained range from GW170817. In this paper, we find that 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 ${M}_{\ensuremath{\bigodot}}$ and the tidal deformability ${\mathrm{\ensuremath{\Lambda}}}_{1.4}={616}_{\ensuremath{-}158}^{+273}$ (based on the assumption that GW190814 is a NS-BH binary) can be satisfied for the slope of symmetry energy $L\ensuremath{\le}50$ MeV. Even including the constraint ${\mathrm{\ensuremath{\Lambda}}}_{1.4}={190}_{\ensuremath{-}120}^{+390}$ 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.