Speaker
Description
Thermal evolution of neutron stars, as well as mass and radius observations, brings about important astrophysical information on properties of highly dense matter in inner core of a neutron star. As a candidate of novel hadronic phase, a coexistent phase of kaon condensation and hyperon-mixed matter [abbreviated to (Y+K) phase] has been extensively studied from both theoretical and observational viewpoints. In the previous studies, however, the (Y+K) phase had a problem that it significantly softens the equation of state (EOS) , so that it cannot give massive neutron stars as large as two solar mass. The problem has been recently solved with inclusion of universal three-body forces between baryons. It has been shown that sufficiently stiff EOS including the (Y+K) phase has been obtained, being enough to be consistent with the observations of masses and radii of massive neutron stars.
In the presence of the (Y+K) phase, the rapid cooling mechanisms via neutrino emissions, i.e., the kaon-induced Urca (KU) processes, become possible.
Recently we have obtained the cooling history of compact stars with the KU processes with use of the EOS including the (Y+K) phase ; The effects of the KU processes on the time evolution of surface temperature have been investigated on the assumption of the density dependence of the proton $^1$S$_0$ pairing strengths.
In this talk, we further discuss in detail main neutrino emission mechanisms unique to the (Y+K) phase by obtaining the density-dependence of neutrino emissivities for the KU processes associated with both nucleons and hyperons ($\Lambda$ and $\Xi^-$ hyperons). We clarify the role of such extra neutrino emission processes on the cooling of neutron stars by comparing with the recently detected cold neutron stars.
| Category | Theory |
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