Strangeness in Neutron Star Cooling

TL;DR

This paper investigates how hyperons and kaons in neutron star cores influence their thermal evolution, highlighting the roles of direct Urca processes in fast cooling and compatibility with observational data.

Contribution

It demonstrates that hyperons enable fast cooling mechanisms and that hyperon or kaon presence in the EOS can align with observed neutron star masses and temperatures.

Findings

Hyperons facilitate faster neutron star cooling via direct Urca processes.

Hyperon presence reduces neutron Fermi momentum, enabling nucleon direct Urca.

EOS with hyperons or kaons can match observational data on neutron star mass and temperature.

Abstract

We study the thermal evolution of neutron stars in the presence of hyperons or kaons in the core. Our results indicate that the nucleon and hyperon direct Urca processes play crucial roles for the cooling of neutron stars. The presence of hyperons drives fast cooling mechanisms in two ways: 1) it allows the hyperon direct Urca prior to the nucleon direct Urca, 2) and it makes the nucleon direct Urca more feasible by reducing the neutron Fermi momentum. We found that the neutron star equation of state (EOS) with hyperons can be consistent with both mass and temperature observations. We also found that the neutron star EOS with kaon condensation can be consistent with observations, even though the cooling behavior is seldom useful to identify or isolate the effect of kaon condensation.