Thermal Evolution of Neutron Stars in 2 Dimensions

TL;DR

This paper models the thermal evolution of rotating, deformed neutron stars in two dimensions using general relativity, revealing how rotation influences cooling patterns, hot spot formation, and core-crust thermal coupling times.

Contribution

It introduces a self-consistent 2D general relativistic framework for neutron star cooling that accounts for rotation-induced deformation and thermal effects, advancing beyond previous 1D models.

Findings

Rotation causes hot spots on neutron star poles.

Rotation increases thermal coupling times between core and crust.

Thermal evolution depends primarily on star frequency, not microscopic core properties.

Abstract

There are many factors that contribute to the breaking of the spherical symmetry of a neutron star. Most notably is rotation, magnetic fields, and/or accretion of matter from companion stars. All these phenomena influence the macroscopic structures of neutron stars, but also impact their microscopic compositions. The purpose of this paper is to investigate the cooling of rotationally deformed, two-dimensional (2D) neutron stars in the framework of general relativity theory, with the ultimate goal of better understand the impact of 2D effects on the thermal evolution of such objects. The equations that govern the thermal evolution of rotating neutron stars are presented in this paper. The cooling of neutron stars with different frequencies is computed self-consistently by combining a fully general relativistic 2D rotation code with a general relativistic 2D cooling code. We show that rotation can significantly influence the thermal evolution of rotating neutron stars. Among the major new aspects are the appearances of hot spots on the poles, and an increase of the thermal coupling times between the core and the crust of rotating neutron stars. We show that this increase is independent of the microscopic properties of the stellar core, but depends only on the frequency of the star.