Strangeness in Neutron Star Cooling

Abstract

Neutron star is a stellar object that can provide us information on the extreme dense matter. At the central part of neutron stars, the exotic states of matter with strangeness are expected to exist due to the fermionic nature of protons and neutrons that are mainly composed of up and down quarks. Strangeness, if exists, softens the neutron star equation of state and reduces the maximum mass of neutron stars. However, due to the recent observations of 2M ⊙ neutron stars, the maximum mass of neutron stars has to be bigger than 2M ⊙ . These recent observations raised questions on the existence of hyperons inside neutron stars, so-called hyperon puzzle. In this talk, we discuss the role of strangeness to the neutron star equation of state and the possibilities of the existence of Λ-hyperons and kaons. We also discuss the cooling behaviours of neutron stars in the presence of strangeness.