Magnetic fields in non-convective regions of stars

TL;DR

This paper reviews the current understanding of magnetic fields in non-convective stellar regions, focusing on observational properties, theoretical models like fossil fields, and magnetic phenomena in different star types including neutron stars.

Contribution

It synthesizes recent developments in magnetic field theories in radiative zones, discusses observational constraints, and explores magnetic field origins in neutron stars, excluding convective dynamo theories.

Findings

Fossil fields explain strong magnetic fields in some stars.

Ap-type stable fields are absent in stars with convective envelopes.

Neutron star magnetic fields may originate from various mechanisms.

Abstract

We review the current state of knowledge of magnetic fields inside stars, concentrating on recent developments concerning magnetic fields in stably stratified (zones of) stars, leaving out convective dynamo theories and observations of convective envelopes. We include the observational properties of A, B and O-type main-sequence stars, which have radiative envelopes, and the fossil field model which is normally invoked to explain the strong fields sometimes seen in these stars. Observations seem to show that Ap-type stable fields are excluded in stars with convective envelopes. Most stars contain both radiative and convective zones, and there are potentially important effects arising from the interaction of magnetic fields at the boundaries between them. Related to this, we discuss whether the Sun could harbour a magnetic field in its core. Recent developments regarding the various convective and radiative layers near the surfaces of early-type stars and their observational effects are examined. We look at possible dynamo mechanisms that run on differential rotation rather than convection. Finally we turn to neutron stars with a discussion of the possible origins for their magnetic fields.