Physics of strongly magnetized neutron stars

TLDR

Recent observations of radio pulsars with extreme spin‑down rates and magnetars provide evidence that some neutron stars possess magnetic fields exceeding the quantum critical value of 4.4 × 10¹³ G. This review examines the exotic physics that emerges in such ultra‑strong magnetic fields, highlighting observational signatures and outstanding theoretical questions. The authors survey the behavior of particles, atoms, plasma, and condensed matter in strong fields, photon propagation and radiative processes, interior physics, field evolution, and decay, and discuss how these processes are applied to models of rotation‑powered pulsars, soft gamma‑ray repeaters, anomalous X‑ray pulsars, and accreting X‑ray pulsars.

Abstract

There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of 4.4 × 1013 G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting gamma-ray sources termed magnetars. This paper will discuss the exotic physics of this high-field regime, where a new array of processes becomes possible and even dominant and where familiar processes acquire unusual properties. We review the physical processes that are important in neutron star interiors and magnetospheres, including the behaviour of free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, free-particle radiative processes, the physics of neutron star interiors and field evolution and decay mechanisms. Application of such processes in astrophysical source models, including rotation-powered pulsars, soft gamma-ray repeaters, anomalous x-ray pulsars and accreting x-ray pulsars will also be discussed. Throughout this review, we will highlight the observational signatures of high magnetic field processes, as well as the theoretical issues that remain to be understood.