Towards a better understanding of the symmetry energy within neutron stars

TL;DR

This paper investigates the symmetry energy within neutron stars by combining gravitational wave data with nuclear experiments, aiming to better understand the microscopic origins of neutron star pressure and improve constraints on the equation of state.

Contribution

It introduces a method to connect nuclear measurements with gravitational wave data to extract the symmetry pressure's density dependence in neutron stars.

Findings

Neutron star radii and tidal deformabilities strongly correlate with pressure at twice saturation density.

Combining GW data with nuclear experiments constrains the symmetry pressure from 1.2 to 4.5 times saturation density.

Uncertainties in symmetry pressure can be reduced with future experimental and astrophysical data.

Abstract

The LIGO-Virgo collaboration ground-breaking detection of the binary neutron-star merger event, GW170817, has expanded efforts to understand the Equation of State (EoS) of nuclear matter. These measurements provide new constraints on the overall pressure, but do not, by itself, elucidate its microscopic origins, including the pressure arising from the symmetry energy, that governs much of the internal structure of a neutron star. To correlate microscopic constraints from nuclear measurements to the GW170817 constraints, we calculate neutron star properties with more than 200 Skyrme energy density functionals that describe properties of nuclei. Calculated neutron-star radii (R) and the tidal deformabilities which show a strong correlation with pressure at twice saturation density. By combining the neutron star EoS extracted from the GW170817 event and the EoS of symmetric matter from nucleus-nucleus collision experiments, we extract the density dependence of the symmetry pressure from 1.2 to 4.5 times saturation density. While the uncertainties in the symmetry pressure are large, they can be reduced with new experimental and astrophysical results.