Rotational evolution of young pulsars due to superfluid decoupling

TL;DR

This paper presents a model explaining the observed braking indices of young pulsars by considering superfluid decoupling in their cores, linking rotational evolution to neutron star internal physics.

Contribution

The study introduces a simple model connecting pulsar spin-down behavior with superfluid decoupling, providing explanations for observed braking indices below 3.

Findings

Model explains braking index n=2.51 of Crab pulsar

Decreasing effective moment of inertia due to superfluidity

Future observations can reveal neutron star properties

Abstract

Pulsars are rotating neutron stars that are seen to slow down, and the spin-down rate is thought to be due to magnetic dipole radiation. This leads to a prediction for the braking index n, which is a combination of spin period and its first and second time derivatives. However, all observed values of n are below the predicted value of 3. Here we provide a simple model that can explain the rotational evolution of young pulsars, including the n=2.51 of the 958-year-old pulsar in the Crab nebula. The model is based on a decrease in effective moment of inertia due to an increase in the fraction of the stellar core that becomes superfluid as the star cools via neutrino emission. The results suggest that future large radio monitoring campaigns of pulsars will yield measurements of the neutron star mass, nuclear equation of state, and superfluid properties.