Light clusters as a possible source of crustal impurities: a quasi-particle approach

TL;DR

This paper investigates whether light clusters like Hydrogen and Helium can serve as impurities in neutron star crusts, using a quasi-particle model to assess their impact on crustal properties.

Contribution

It introduces a quasi-particle approach with in-medium effects to evaluate light cluster impurities in neutron star crusts, considering various relativistic mean field models.

Findings

Impurity factor from light clusters is very small.

Model dependence affects impurity estimates.

Light clusters can be neglected in transport calculations.

Abstract

The presence of impurities in the neutron star crust is known to affect in an important way the thermal and electrical conductivity of the star. In this work, we explore the possibility that such impurities might arise from the simultaneous presence of heavy ions together with Hydrogen and Helium isotopes formed during the cooling process of the star. We consider an equilibrium population of such light particles at temperatures close to the crystallization of the crust within an effective quasi-particle approach including in-medium binding energy shifts, and using different versions of the relativistic mean field approach for the crustal modeling. Thermal effects are consistently included also in the dominant ion species present in each crustal layer described in the compressible liquid drop approximation. We find that the impurity factor associated to light clusters is comparatively very small and can be neglected in transport calculations, even if a strong model dependence is observed.