Thermal evolution of massive compact objects with dense quark cores

TL;DR

This paper investigates how the presence and type of quark pairing in dense stellar cores influence the thermal cooling behavior of massive compact stars, providing insights into their internal composition through observable temperature data.

Contribution

It introduces a detailed modeling of quark pairing effects on neutron star cooling, including inhomogeneous gapless phases, and compares these models with observational data.

Findings

Massive stars with unpaired blue quarks cool faster in the neutrino era.

Cooling curves vary significantly with star mass and core composition.

Fast neutrino cooling stars become hotter than slow cooling ones at late times.

Abstract

We examine the thermal evolution of a sequence of compact objects containing low-mass hadronic and high-mass quark-hadronic stars constructed from a microscopically motivated equation of state. The dependence of the cooling tracks in the temperature versus age plane is studied on the variations of the gaplessness parameter (the ratio of the pairing gap for red-green quarks to the electron chemical potential) and the magnitude of blue quark gap. The pairing in the red-green channel is modeled assuming an inhomogeneous superconducting phase to avoid tachionic instabilities and anomalies in the specific heat; the blue colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor. We find that massive stars containing quark matter cool faster in the neutrino-cooling era if one of the colors (blue) is unpaired and/or the remaining colors (red-green) are paired in a inhomogeneous gapless superconducting state. The cooling curves show significant variations along the sequence, as the mass (or the central density) of the models is varied. This feature provides a handle for fine-tuning the models to fit the data on the surface temperatures of same-age neutron stars. In the late-time photon cooling era we observe inversion in the temperature arrangement of models, i.e., stars experiencing fast neutrino cooling are asymptotically hotter than their slowly cooling counterparts.