Landau quantization and neutron emissions by nuclei in the crust of a magnetar

TL;DR

This paper investigates how strong magnetic fields in magnetar crusts influence neutron emissions and Landau quantization effects, using various nuclear models to analyze the shifts in neutron-drip transition densities.

Contribution

It provides a comprehensive analysis of the impact of magnetic fields on neutron-drip transition densities in magnetar crusts using multiple microscopic nuclear models.

Findings

Landau quantization shifts neutron-drip transition densities.

Quantum oscillations of threshold density are universal across models.

Nuclear uncertainties affect equilibrium composition predictions.

Abstract

Magnetars are neutron stars endowed with surface magnetic fields of the order of $10^{14}-10^{15}$~G, and with presumably much stronger fields in their interior. As a result of Landau quantization of electron motion, the neutron-drip transition in the crust of a magnetar is shifted to either higher or lower densities depending on the magnetic field strength. The impact of nuclear uncertainties is explored considering the recent series of Brussels-Montreal microscopic nuclear mass models. All these models are based on the Hartree-Fock-Bogoliubov method with generalized Skyrme functionals. They differ in their predictions for the symmetry energy coefficient at saturation, and for the stiffness of the neutron-matter equation of state. For comparison, we have also considered the very accurate but more phenomenological model of Duflo and Zuker. Although the equilibrium composition of the crust of a magnetar and the onset of neutron emission are found to be model dependent, the quantum oscillations of the threshold density are essentially universal.