Neutron stars and their magnetic fields

TL;DR

This review explains the physics behind neutron stars' extremely strong magnetic fields, emphasizing the role of quantum degeneracy and charged particles in sustaining these fields over time.

Contribution

It provides a pedagogical overview of the physical principles underlying neutron star magnetic fields, including their origin, stability, and relation to observed phenomena.

Findings

Neutron stars' magnetic fields are supported by degenerate charged particles.

Quantum degeneracy prevents rapid decay of magnetic fields.

Charged particles enable long-term magnetic field stability.

Abstract

Neutron stars have the strongest magnetic fields known anywhere in the Universe. In this review, I intend to give a pedagogical discussion of some of the related physics. Neutron stars exist because of Pauli's exclusion principle, in two senses: 1) It makes it difficult to squeeze particles too close together, in this way allowing a mechanical equilibrium state in the presence of extremely strong gravity. 2) The occupation of low-energy proton and electron states makes it impossible for low-energy neutrons to beta decay. A corollary of the second statement is that charged particles are necessarily present inside a neutron star, allowing currents to flow. Since these particles are degenerate, they collide very little, and therefore make it possible for the star to support strong, organized magnetic fields over long times. These show themselves in pulsars and are the most likely energy source for the high X-ray and gamma-ray luminosity ``magnetars''. I briefly discuss the possible origin of this field and some physical constraints on its equilibrium configurations.