The role of $r$-mode damping in the thermal evolution of neutron stars

TL;DR

This paper models neutron star thermal evolution by coupling it with r-mode instability dynamics, showing that damping effects can explain observed temperatures without exotic matter, and revealing a complex interplay of heating and cooling.

Contribution

It introduces a second order model coupling r-mode evolution with thermal history, demonstrating that damping effects can account for high temperatures without superfluidity or exotic particles.

Findings

Shear viscous damping explains high temperatures of young pulsars.

Predicted light curves can cover all young and middle-aged pulsars.

Radiative viscous damping can cause additional cooling effects.

Abstract

The thermal evolution of neutron stars (NSs) is investigated by coupling with the evolution of $\textit{r}$-mode instability that is described by a second order model.The heating effect due to shear viscous damping of the $\textit{r}$-modes enables us to understand the high temperature of two young pulsars (i.e., PSR B0531+21 and RX J0822-4300) in the framework of the simple $npe$ NS model, without superfluidity or exotic particles.Moreover, the light curves predicted by the model within an acceptable parameter regime may probably cover all of the young and middle-aged pulsars in the $\lg T_s^{\infty}-\lg t$ panel, and an artificially strong $p$ superfluidity invoked in some early works is not needed here. Additionally, by considering the radiative viscous damping of the $\textit{r}$-modes, a surprising extra cooling effect is found, which can even exceed the heating effect sometimes although plays an ignorable role in the thermal history.