Neutron Star Cooling Within the Equation of State With Induced Surface Tension

Stefanos Tsiopelas,Violetta Sagun

doi:10.3390/particles3040045

Abstract

We study the thermal evolution of neutron stars described within the equation of state with induced surface tension (IST) that reproduces properties of normal nuclear matter, fulfills the proton flow constraint, provides a high-quality description of hadron multiplicities created during the nuclear-nuclear collision experiments, and it is equally compatible with the constraints from astrophysical observations and the GW170817 event. The model features strong direct Urca processes for the stars above 1.91M⊙. The IST equation of state shows very good agreement with the available cooling data, even without introducing nuclear pairing. We also analysed the effect of the singlet proton/neutron and triplet neutron pairing on the cooling of neutron stars of different mass. We show that the description of the compact object in the center of the Cassiopeia A does not necessarily require an inclusion of neutron superfluidity and/or proton superconductivity. Our results indicate that data of Cassiopeia A can be adequately well reproduced by a 1.66M⊙ star with an atmosphere of light elements. Moreover, the IST EoS reproduces each of the observational datasets for the surface temperature of Cassiopeia A either by a rapidly cooling ∼1.955M⊙ star with paired and unpaired matter or by a 1.91M⊙ star with the inclusion of neutron and proton pairings in the singlet channel.

Highlights

Born out of supernova explosions, neutron stars (NSs) are considered to start their life having very high internal temperatures and cool down through a combination of thermal radiation from their surface and neutrino emission from their interior
We focused on the thermal evolution of NSs without any sort of pairing between the nucleons
In order to model the uncertainties of the heat-blanketing effect of the envelope, we compare the thermal evolution of NSs with a non-accreted envelope containing heavy elements with the envelope containing light elements

Summary

Introduction

Born out of supernova explosions, neutron stars (NSs) are considered to start their life having very high internal temperatures and cool down through a combination of thermal radiation from their surface and neutrino emission from their interior. From the first day of their lives, when the temperature of their interior has already dropped from ∼1011 K to ∼109−10 K making it transparent to neutrinos, up until the first million years of their existence, thermal energy is mainly carried away in the form of neutrino radiation During this time, measurements of surface temperature and luminosity of the stars can provide significant information about the properties of matter in their depth, since the thermal evolution depends on factors, such as the internal composition and the thermodynamic properties of matter, are defined by the Equation of State (EoS), the chemical abundances of the envelope, and the type of pairing between the constituent particles.

Equation of State

Cooling Processes

Results

Conclusions