Combined Constraints on the Equation of State of Dense Neutron-Rich Matter from Terrestrial Experiments and Observations of Neutron Stars

Abstract

Within the parameter space of equation of state (EOS) of dense neutron-rich matter limited by existing constraints mainly from terrestrial nuclear experiments, we investigate how the neutron star maximum mass $M_{\max }>2.01\pm 0.04$ M${}_{\odot }$, radius $10.62<R_{1.4}<12.83$ km and tidal deformability ${\Lambda }_{1.4}\le 800$ of canonical neutron stars all together constrain the EOS of dense neutron-rich nucleonic matter. While the 3-D parameter space of $K_{\mathrm{sym}}$ (curvature of nuclear symmetry energy), $J_{\mathrm{sym}}$ and $J_0$ (skewness of the symmetry energy and EOS of symmetric nuclear matter, respectively) are narrowed down significantly by the observational constraints, more data are needed to pin down the individual values of $K_{\mathrm{sym}}$, $J_{\mathrm{sym}}$ and $J_0$ with quantified uncertainties. The $J_0$ largely controls the maximum mass of neutron stars. While the EOS with $J_0=0$ is sufficiently stiff to support neutron stars as massive as 2.37 M${}_{\odot }$, to support the hyperthetical ones as massive as 2.74 M${}_{\odot }$ (composite mass of GW170817) requires $J_0$ to be larger than its currently known maximum value of about 400 MeV and beyond the causality limit. The upper limit on the tidal deformability of ${\Lambda }_{1.4}=800$ from the recent observation of GW170817 is found to provide upper limits on some EOS parameters consistent with but far less restrictive than the existing constraints of other observables studied.

Comments: More discussions on parameterizing the EOS of dense neutron-rich matter and why we do NOT use the widely used polytropes are added. The Astrophysical Journal in press