Deformed crystals and torsional oscillations of neutron star crust

TL;DR

This paper investigates the breaking stress of Coulomb crystals in neutron star crusts considering electron screening, and derives analytic formulas for torsional oscillation frequencies, aiding modeling of neutron star phenomena.

Contribution

It provides a new calculation of breaking stress including electron screening effects and exact formulas for torsional mode frequencies in neutron star crusts.

Findings

Breaking stress depends on electron screening parameter.

Torsional oscillation frequencies are unaffected by the outer crust.

Analytic expressions for fundamental frequencies are derived.

Abstract

We study breaking stress of deformed Coulomb crystals in a neutron star crust, taking into account electron plasma screening of ion-ion interaction; calculated breaking stress is fitted as a function of electron screening parameter. We apply the results for analyzing torsional oscillation modes in the crust of a non-magnetic star. We present exact analytic expression for the fundamental frequencies of such oscillations and show that the frequencies of all torsional oscillations are insensitive to the presence of the outer neutron star crust. The results can be useful in theoretical modeling of processes involving deformed Coulomb crystals in the crust of neutron stars, such as magnetic field evolution, torsional crustal or thermo-elastic quasi-periodic oscillations of flaring soft gamma-ray repeaters, pulsar glitches. The applicability of the results to soft gamma-ray repeaters is discussed.