Impact of the symmetry energy on the outer crust of non-accreting neutron stars

TL;DR

This study investigates how the symmetry energy influences the composition and structure of the outer crust of non-accreting neutron stars, revealing that stiffer symmetry energy models lead to more neutron-rich crustal nuclei.

Contribution

It demonstrates the correlation between symmetry energy stiffness and crust composition using realistic nuclear mass tables and a simplified model.

Findings

Stiffer symmetry energy models predict more neutron-rich crustal nuclei.

A correlation exists between neutron skin thickness of 208Pb and crust composition.

Models with large neutron skins produce more exotic crust compositions.

Abstract

The composition and equation of state of the outer crust of non-accreting neutron stars is computed using accurate nuclear mass tables. The main goal of the present study is to understand the impact of the symmetry energy on the structure of the outer crust. First, a simple "toy model" is developed to illustrate the competition between the electronic density and the symmetry energy. Then, realistic mass tables are used to show that models with a stiff symmetry energy - those that generate large neutron skins for heavy nuclei - predict a sequence of nuclei that are more neutron-rich than their softer counterparts. This result may be phrased in the form of a correlation: the larger the neutron skin of 208Pb, the more exotic the composition of the outer crust.