Journal Article

A highly resistive layer within the crust of X-ray pulsars limits their spin periods

Pons, José A., Rea, Nanda, Viganò, Daniele

2013

Overview

The lack of isolated X-ray pulsars with spin periods longer than 12 s raises the question of where the population of evolved high-magnetic-field neutron stars has gone. Unlike canonical radiopulsars, X-ray pulsars are not subject to physical limits to the emission mechanism nor observational biases against the detection of sources with longer periods. Here we show that a highly resistive layer in the innermost part of the crust of neutron stars naturally limits the spin period to a maximum value of about 10–20 s. This highly resistive layer is expected if the inner crust is amorphous and heterogeneous in nuclear charge, possibly owing to the existence of a nuclear ‘pasta’ phase. Our findings suggest that the maximum period of isolated X-ray pulsars may be the first observational evidence for an amorphous inner crust, whose properties can be further constrained by future X-ray timing missions combined with more detailed models. A pulsar is a rotating neutron star that beams out electromagnetic waves. The absence of isolated X-ray pulsars with periods longer than 12 s could be a clue to the structural composition of a neutron star’s crust, as simulations show that an amorphous layer would prevent a pulsar from spinning down.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/766/33/34/867 / Astrophysics / Atomic / Charge / Classical and Continuum Physics / Complex Systems / Condensed Matter Physics / Crusts / Emissions / Emissions control / Mathematical and Computational Physics / Molecular / Neutron stars / Optical and Plasma Physics / Pasta / Physics / Pulsars / Stars & galaxies / Theoretical / Time measurements / X-rays