Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust

TL;DR

This paper analyzes how neutron degeneracy and plasma effects significantly enhance radiative neutron capture rates in neutron star crusts, providing analytical formulas and discussing implications for astrophysical processes.

Contribution

It introduces simple analytical expressions for reaction rates considering neutron degeneracy and plasma effects, improving accuracy over standard models.

Findings

Neutron degeneracy can increase reaction rates by orders of magnitude.

Plasma effects on radiative transitions also significantly enhance reaction rates.

Reaction rates depend strongly on temperature and neutron chemical potential.

Abstract

We consider the astrophysical reaction rates for radiative neutron capture reactions ($n,\gamma$) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse ($\gamma,n$) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.