Properties of the neutron star crust: Quantifying and correlating uncertainties with improved nuclear physics

TL;DR

This study uses a compressible liquid-drop model combined with chiral effective field theory to analyze uncertainties in neutron star crust properties, revealing how nuclear physics uncertainties influence crust composition, transition points, and global neutron star characteristics.

Contribution

It introduces a unified approach linking crust and core properties of neutron stars with nuclear Hamiltonian uncertainties, improving understanding of crust composition and transition uncertainties.

Findings

Finite-size effects impact crust composition but not isospin asymmetry.

Uncertainties in nuclear Hamiltonians strongly affect crust-core transition location.

Unified modeling tightens correlations between neutron star global properties and nuclear physics uncertainties.

Abstract

A compressible liquid-drop model (CLDM) is used to correlate uncertainties associated with the properties of the neutron star (NS) crust with theoretical estimates of the uncertainties associated with the equation of state (EOS) of homogeneous neutron and nuclear matter. For the latter, we employ recent calculations based on Hamiltonians constructed using Chiral Effective Field theory. Fits to experimental nuclear masses are employed to constrain the CLDM further, and we find that they disfavor some of the Chiral Hamiltonians. The CLDM allows us to study the complex interplay between bulk, surface, curvature, and Coulomb contributions, and their impact on the NS crust. It also reveals how the curvature energy alters the correlation between the surface energy and the bulk symmetry energy. Our analysis quantifies how the uncertainties associated with the EOS of homogeneous matter implies significant uncertainties for the composition of the crust, its proton fraction, and the volume fraction occupied by nuclei. We find that the finite-size effects impact the crust composition, but have a negligible effect on the net isospin asymmetry of matter. The isospin asymmetry is largely determined by the bulk properties and the isospin dependence of the surface energy. The most significant uncertainties associated with matter properties in the densest regions of the crust, the precise location of the crust-core transition, are found to be strongly correlated with uncertainties associated with the Hamiltonians. By adopting a unified model to describe the crust and the core of NSs, we tighten the correlation between their global properties such as their mass-radius relationship, moment of inertia, crust thickness, and tidal deformability with uncertainties associated with the nuclear Hamiltonians.