Models of crustal heating in accreting neutron stars

TL;DR

This study reevaluates crustal heating in accreting neutron stars by considering recent neutrino loss suppression, different initial compositions, and reaction uncertainties, showing consistent results with previous models and weak dependence on reaction details.

Contribution

It introduces a simplified model for crustal heating that aligns with complex simulations and explores the effects of composition and reaction uncertainties.

Findings

Total crustal heat per nucleon ranges from 1.5 to 1.9 MeV.

Results agree with multicomponent plasma simulations.

Crustal heat is insensitive to reaction distribution details.

Abstract

Heating associated with non-equilibrium nuclear reactions in accreting neutron-star crusts is reconsidered, taking into account suppression of neutrino losses demonstrated recently by Gupta et al. Two initial compositions of the nuclear burning ashes, A=56 and A=106, are considered. Dependence of the integrated crustal heating on uncertainties plaguing pycnonuclear reaction models is studied. One-component plasma approximation is used, with compressible liquid-drop model of Mackie and Baym to describe nuclei. Evolution of a crust shell is followed from 10^8 g/cm^3 to 10^(13.6) g/cm^3 The integrated heating in the outer crust agrees nicely with results of self-considtent multicomponent plasma simulations of Gupta et al.; their results fall between our curves obtained for A=56 and A=106. Total crustal heat per one accreted nucleon ranges between 1.5 MeV to 1.9 MeV for A=106 and A=56, respectively. The value of total crustal heat per nucleon depends weakly on the presence of pycnonuclear reactions at densities 10^(12)-10^(13) g/cm^3. Remarkable insensitivity of the total crustal heat on the details of the distribution of nuclear processes in accreted crust is explained.