Nonequilibrium thermodynamics of accreted neutron-star crust

TL;DR

This paper introduces a new thermodynamic potential for modeling the inner crust of accreting neutron stars, enabling better predictions of heat release and aiding in the interpretation of observational data.

Contribution

It proposes using a different thermodynamic potential, $\Psi$, instead of Gibbs free energy, for accurate crust modeling of accreting neutron stars.

Findings

Derived the thermodynamic potential $\Psi$ for neutron-star crusts.

Calculated heat-release distribution due to nuclear reactions.

Enhanced understanding of accreted crust thermodynamics.

Abstract

We show that, in order to determine the equation of state of the inner crust of an accreting neutron star, one should minimize not the Gibbs free energy, as it is generally assumed in the literature, but a different thermodynamic potential $\Psi$, which tends to the minimum at fixed pressure and neutron chemical potential. Once this potential is specified, one can calculate the heat-release distribution in the stellar crust due to nonequilibrium nuclear reactions induced by accretion of matter onto the neutron-star surface. The results are important for adequate modeling of the accreted crust and interpretation of the observations of accreting neutron stars in low-mass X-ray binaries.