Flux-Vortex Pinning and Neutron Star Evolution

TL;DR

This paper discusses how flux-vortex pinning in neutron star cores explains the reduction of magnetic dipole moments during binary evolution, particularly in low mass X-ray binaries and millisecond pulsars.

Contribution

It provides a detailed mechanism linking vortex pinning to magnetic field decay, emphasizing its role during neutron star spin-down in binary systems.

Findings

Pinning mechanism reduces magnetic dipole moment during spin-down.

Flux vortex pinning is ineffective in young pulsars but active during binary evolution.

The mechanism operates even with vortex creep present.

Abstract

G. Srinivasan et al. (1990) proposed a simple and elegant explanation for the reduction of the neutron star magnetic dipole moment during binary evolution leading to low mass X-ray binaries and eventually to millisecond pulsars: Quantized vortex lines in the neutron star core superfluid will pin against the quantized flux lines of the proton superconductor. As the neutron star spins down in the wind accretion phase of binary evolution, outward motion of vortex lines will reduce the dipole magnetic moment in proportion to the rotation rate. The presence of a toroidal array of flux lines makes this mechanism inevitable and independent of the angle between the rotation and magnetic axes. The incompressibility of the flux-line array (Abrikosov lattice) determines the epoch when the mechanism will be effective throughout the neutron star. Flux vortex pinning will not be effective during the initial young radio pulsar phase. It will, however, be effective and reduce the dipole moment in proportion with the rotation rate during the epoch of spindown by wind accretion as proposed by Srinivasan et al. The mechanism operates also in the presence of vortex creep.