Not an Oxymoron: Some X-ray Binary Pulsars with Enormous Spinup Rates Reveal Weak Magnetic Fields

TL;DR

This paper proposes that some X-ray binary pulsars with high spinup rates have weak magnetic fields, challenging traditional models and suggesting a new theory of extreme accretion phenomena far from equilibrium.

Contribution

It introduces a novel scenario where weak magnetic fields allow magnetospheres to be crushed, explaining enormous spinup rates without requiring unphysically high magnetic fields.

Findings

Weak magnetic fields in certain pulsars allow magnetospheres to be crushed by inflowing matter.

Enormous spinup rates occur before matter reaches the pulsar surface, via angular momentum transfer in the inner disk.

The mechanism can also cause pulsar spin-down when the magnetosphere expands beyond corotation.

Abstract

Three high-mass X-ray binaries have been discovered recently exhibiting enormous spinup rates. Conventional accretion theory predicts extremely high surface dipolar magnetic fields that we believe are unphysical. Instead, we propose quite the opposite scenario: some of these pulsars exhibit weak magnetic fields, so much so that their magnetospheres are crushed by the weight of inflowing matter. The enormous spinup rate is achieved before inflowing matter reaches the pulsar's surface as the penetrating inner disk transfers its excess angular momentum to the receding magnetosphere which, in turn, applies a powerful spinup torque to the pulsar. This mechanism also works in reverse: it spins a pulsar down when the magnetosphere expands beyond corotation and finds itself rotating faster than the accretion disk which then exerts a powerful retarding torque to the magnetic field and to the pulsar itself. The above scenaria cannot be accommodated within the context of neutron-star accretion processes occurring near spin equilibrium, thus they constitute a step toward a new theory of extreme (far from equilibrium) accretion phenomena.