Cooling properties of Cloudy Bag strange stars

Abstract

As the chiral symmetry is widely recognized as an important driver of the strong interaction dynamics, current strange stars models based on MIT bag models do not obey such symmetry. We investigate properties of bare strange stars using the Cloudy Bag model, in which a pion cloud coupled to the quark-confining bag is introduced such that chiral symmetry is conserved. The parameters in the model, namely the bag constant and strange quark mass are determined self-consistently by fitting the mass spectrum of baryons. Then the equation of state is obtained by evaluating the energy–momentum tensor of the system. We find that the stellar properties of the Cloudy Bag strange stars are similar to those of MIT Bag models. However, the decay of pions is a very efficient cooling way. In fact it can carry out most the thermal energy in a few milliseconds and directly convert them into 100 MeV photons via pion decay. This may be a very efficient γ-ray burst mechanism. Numerical results indicate that temperature of a Cloudy Bag strange star is sufficiently lower than a MIT one for the small gap energy of color superconductivity ( Δ=1 MeV). On the other hand, large gap energy ( Δ=100 MeV) can suppress the pion emissivity and hence the cooling curves of Cloudy model and MIT model are almost identical. The long term cooling behaviors of both MIT model and Cloudy model are determined by the color–flavor locked phase. The surface luminosity of a bare strange star is higher than that of a neutron star until 10 6 and 10 8 s for ( Δ=100 MeV) and ( Δ=1 MeV) respectively. After this period, the surface luminosity of a bare strange star becomes lower than that of a neutron star even rapidly cooling mechanisms, e.g. direct URCA process or pion condensation, exist in the neutron stars. Hence, the cooling behavior may provide a possible way to distinguish a compact object between a neutron star, MIT strange star and Cloudy Bag strange star in observations.