The apparent decay of pulsar magnetic fields

TL;DR

This study investigates the decay of magnetic fields in neutron stars by analyzing 76 pulsars, finding a slow power-law decay that suggests crusts are nearly impurity-free, leading to minimal magnetic field decay over time.

Contribution

The paper introduces a novel method to estimate pulsar magnetic fields and provides the first empirical evidence for a slow, power-law decay of magnetic fields in neutron stars.

Findings

Magnetic field decay follows a power-law with index approximately 0.19.

The decay rate is consistent with neutron star crusts being nearly impurity-free.

Observational selection effects set an upper limit on the intrinsic decay rate.

Abstract

Neutron stars are extremely strong cosmic magnets which fields are expected to decay with time. Here we report on the simple test of this process. Adopting a novel approach, we have estimated surface magnetic fields $B$ for 76 radiopulsars (the most numerous subclass of the known isolated neutron stars) which ages $t$ are known independently. Focusing on the accurate evaluation of the precision of both quantities, we determined a significant power-law trend $B(t) \propto t^{-\beta}$ with index $\beta = 0.19^{+0.05}_{-0.06}$ at 95\% C.L. The effects of the observational selection turn this value into the upper limit for the intrinsic field decay rate. If so, then neutron star crusts are close to the "impurity-free crystals", which results in a relatively slow magnetic fields decay.