Relativistic mechanics of neutron superfluid in (magneto) elastic star crust

TL;DR

This paper develops a unified relativistic framework combining elasticity and superfluidity to model neutron star crusts, accounting for superfluid neutrons penetrating the solid lattice at high densities.

Contribution

It introduces a novel combined relativistic model for neutron star crusts that incorporates both elastic and superfluid behaviors within a single Lagrangian formalism.

Findings

Unified relativistic elasticity and superfluidity models developed

Models include both vortex-free and vortex-pinned scenarios

Applicable to high-density neutron star crusts

Abstract

At densities below the neutron drip threshold, a purely elastic solid model (including, if necessary, a frozen-in magnetic field) can provide an adequate description of a neutron star crust, but at higher densities it will be necessary to allow for the penetration of the solid lattice by an independently moving current of superfluid neutrons. In order to do this, the previously available category of relativistic elasticity models is combined here with a separately developed category of relativistic superfluidity models in a unified treatment based on the use of an appropriate Lagrangian master function. As well as models of the purely variational kind, in which the vortices flow freely with the fluid, such a master function also provides a corresponding category of non-dissipative models in which the vortices are pinned to the solid structure.