Influence of the nuclear symmetry energy on the structure and composition of the outer crust

Abstract

We review and extend with nonrelativistic nuclear mean field calculations a previous study of the impact of the nuclear symmetry energy on the structure and composition of the outer crust of nonaccreting neutron stars. First, we develop a simple "toy model" to understand the most relevant quantities determining the structure and composition of the outer crust: the nuclear symmetry energy and the pressure of the electron gas. While the latter is a well determined quantity, the former ---specially its density dependence--- still lacks an accurate characterization. We thus focus on the influence of the nuclear symmetry energy on the crustal composition. For that, we employ different nuclear models that are accurate in the description of terrestrial nuclei. We show that those models with stiffer symmetry energies ---namely, those that generate thicker neutron skins in heavy nuclei and have smaller symmetry energies at subnormal nuclear densities--- generate more exotic isotopes in the stellar crust than their softer counterparts.