Internal Heating of Old Neutron Stars: Contrasting Different Mechanisms

TL;DR

This paper investigates various internal heating mechanisms in old neutron stars, especially millisecond pulsars, to explain observed thermal emissions, highlighting rotochemical heating and vortex creep as significant contributors.

Contribution

The study compares different internal heating mechanisms in neutron stars, emphasizing the importance of rotochemical heating and vortex creep in thermal evolution models.

Findings

Crust cracking does not produce detectable heating.

Rotochemical heating and vortex creep significantly affect neutron star temperatures.

Heating mechanisms depend on pulsar spin-down parameters.

Abstract

The thermal emission detected from the millisecond pulsar J0437-4715 is not explained by standard cooling models of neutron stars without a heating mechanism. We investigated three heating mechanisms controlled by the rotational braking of the pulsar: breaking of the solid crust, superfluid vortex creep, and non-equilibrium reactions ('rotochemical heating'). We find that the crust cracking mechanism does not produce detectable heating. Given the dependence of the heating mechanisms on spin-down parameters, which leads to different temperatures for different pulsars, we study the thermal evolution for two types of pulsars: young, slowly rotating 'classical' pulsars and old, fast rotating millisecond pulsars (MSPs). We find that the rotochemical heating and vortex creep mechanism can be important both for classical pulsars and MSPs.