Towards mitigation of apparent tension between nuclear physics and astrophysical observations by improved modeling of neutron star matter

Abstract

Observations of neutron stars (NSs) by the LIGO-Virgo and NICER collaborations have provided reasonably precise measurements of their various macroscopic properties. In this paper, we employ a Bayesian framework to combine them and place improved joint constraints on the properties of the NS equation of state (EOS). We use a hybrid EOS formulation that employs a parabolic expansion-based nuclear empirical parametrization around the nuclear saturation density augmented by a generic 3-segment piecewise polytrope model at higher densities. Within the 90% credible level this parametrization predicts ${R}_{1.4}={12.57}_{\ensuremath{-}0.92}^{+0.73}\text{ }\text{ }\mathrm{km}$ and ${\mathrm{\ensuremath{\Lambda}}}_{1.4}={550}_{\ensuremath{-}225}^{+223}$ for the radius and dimensionless tidal deformability, respectively, of a $1.4\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ NS. Finally, we show how the construction of the full NS EOS based solely on the nuclear empirical parameters at saturation density leads to certain tension with the astrophysical data, and how the hybrid approach provides a resolution to it.