Cooling of neutron stars with quark-hadron continuity

Tsuneo Noda,Nobutoshi Yasutake,Masa-Aki Hashimoto,Toshiki Maruyama,Toshitaka Tatsumi,W Liu,Y Wang,X Tang,S Zeng,B Guo

doi:10.1051/epjconf/202226011024

Abstract

Neutron stars are high-density objects formed by the gravitational collapse of massive stars, and the whole star can be likened to a giant nucleus. The interior of a neutron star is considered to contain exotic particles and states which do not appear in a normal nucleus. The internal states are constrained by observations of masses and radii via the equation of state of highly dense nuclear matter. Within these constraints, a variety of exotic states have been discussed. The internal state of neutron stars is closely related to its neutrino emission process, which cools the star from the inside. This effect can be compared with observations of the surface temperature of neutron stars. However, despite the wide range of observations of neutron stars, the nature of the neutron star matter remains uncertain. We consider quark matter as an exotic state and perform cooling calculations for neutron stars, incorporating the effects of nucleon superﬂuidity and quark colour superconductivity.We take into account the “quark-hadron continuity”, in which the neutron superﬂuidity is succeeded by thedquark pairing. Furthermore, we obtained the range of the neutron star cooling curve, taking into account the difference in surface temperature due to the composition of the surface layer. We found that the existence of quark matter causes strong neutrino emission from quarks, which is moderately suppressedbysuperﬂuidity and superconductivity, and canexplain the cold surface temperature of neutron stars.

Highlights

Neutron stars are extremely dense objects, which can be likened to giant atomic nuclei
Exotic states are explored in the terrestrial experiments, but the internal states of neutron stars are relatively cold compared to their density, and it is very difficult to reproduce them in heavy-ion collisions
We investigate the thermal evolution of neutron stars by constructing a model of the neutron star cooling, considering the equation of state (EoS) in which nucleons decay into quark matter at high densities

Summary

Introduction

Neutron stars are extremely dense objects, which can be likened to giant atomic nuclei. Neutrino emission is strongly dependent on the state of the dense nuclear matter inside, and there is a strong relationship between the cooling of the neutron star and the state of the dense nuclear matter. To account for the observed temperatures of neutron stars, we would need a strong neutrino emission process, such as the DU process, or an exotic state with similar strong cooling which are only valid for some stars.

Results

Conclusion