Origin of neutron star magnetic fields

TL;DR

This paper explores the origins and evolution of neutron star magnetic fields, emphasizing core collapse dynamo mechanisms and the importance of magnetic stability and helicity in their long-term configuration.

Contribution

It proposes that differential rotation and magnetorotational instability during core collapse are key to magnetic field generation in neutron stars, especially magnetars.

Findings

Differential rotation likely drives magnetic field amplification during core collapse.

Magnetic instabilities pose a risk of field decay after formation.

Stable magnetic configurations may result from magnetic helicity conservation.

Abstract

Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritance is not sufficient to explain the fields of magnetars. Energetic considerations point to differential rotation in the final stages of core collapse process as the most likely source of field generation, at least for magnetars. A runaway phase of exponential growth is needed to achieve sufficient field amplification during relevant phase of core collapse; it can probably be provided by a some form of magnetorotational instability. Once formed in core collapse, the field is in danger of decaying again by magnetic instabilities. The evolution of a magnetic field in a newly formed neutron star is discussed, with emphasis on the existence of stable equilibrium configurations as end products of this evolution, and the role of magnetic helicity in their existence.