Unified Equation of State for Neutron Stars Based on the Gogny Interaction

TL;DR

This paper develops new Gogny interaction parametrizations that produce a stiffer neutron star equation of state, enabling accurate predictions of neutron star maximum masses around two solar masses while maintaining good finite nuclei properties.

Contribution

The authors introduce modified Gogny parametrizations with adjusted symmetry energy density dependence, resulting in a stiffer EoS suitable for neutron star modeling and consistent finite nuclei predictions.

Findings

New Gogny parametrizations predict neutron star maximum masses around two solar masses.

The Gogny-based EoS aligns with other models in properties like moment of inertia and tidal deformability.

Core-crust transition properties are consistent with observational constraints.

Abstract

The most popular Gogny parametrizations, namely D1S, D1N and D1M, describe accurately the ground-state properties of spherical and deformed finite nuclei all across the mass table obtained with Hartree--Fock--Bogoliubov (HFB) calculations. However, these forces produce a rather soft equation of state (EoS) in neutron matter, which leads to predict maximum masses of neutron stars well below the observed value of two solar masses. To remove this limitation, we built new Gogny parametrizations by modifying the density dependence of the symmetry energy predicted by the force in such a way that they can be applied to the neutron star domain and can also reproduce the properties of finite nuclei as good as their predecessors. These new parametrizations allow us to obtain stiffer EoS's based on the Gogny interactions, which predict maximum masses of neutron stars around two solar masses. Moreover, other global properties of the star, such as the moment of inertia and the tidal deformability, are in harmony with those obtained with other well tested EoSs based on the SLy4 Skyrme force or the Barcelona--Catania--Paris--Madrid (BCPM) energy density functional. Properties of the core-crust transition predicted by these Gogny EoSs are also analyzed. Using these new Gogny forces, the EoS in the inner crust is obtained with the Wigner--Seitz approximation in the Variational Wigner--Kirkwood approach along with the Strutinsky integral method, which allows one to estimate in a perturbative way the proton shell and pairing corrections. For the outer crust, the EoS is determined basically by the nuclear masses, which are taken from the experiments, wherever they are available, or by HFB calculations performed with these new forces if the experimental masses are not known.