The spin evolution of neutron stars with the superfluid core

TL;DR

This paper models the spin evolution of neutron stars with superfluid cores, revealing that superfluidity accelerates inclination angle changes and influences pulsar alignment, with implications for understanding neutron star behavior.

Contribution

It introduces a two-component model including superfluid neutrons and analyzes their impact on neutron star spin evolution, which was not thoroughly explored before.

Findings

Superfluid core accelerates inclination angle evolution.

Neutron stars tend to evolve to orthogonal or coaxial states.

Rapid evolution may conflict with observational data.

Abstract

We investigate the neutron stars spin evolution (breaking, inclination angle evolution and radiative precession), taking into account the superfluidity of the neutrons in the star core. The neutron star is treated as a two-component system consisting of a "charged" component (including the crust and the core protons, electrons and normal neutrons) and a core superfluid neutron component. The components are supposed to interact through the mutual friction force. We assume that the "charged" component rotates rigidly. The neutron superfluid velocity field is calculated directly from linearized hydrodynamical equations. It is shown that the superfluid core accelerates the evolution of inclinaton angle and makes all pulsars evolve to either orthogonal or coaxial state. However, rapid evolution seems to contradict the observation data. Obtained results together with the observations may allow to examine the superfluid models.