Equations of state for mixed stars

Abstract

We investigate the properties of mixed stars formed by hadronic and quark matter in β-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. We use the non-linear Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio models for the quark matter. The calculations were performed for T = 0 and for finite temperatures in order to describe neutron and proto-neutron stars. The star properties are discussed. Both the Bag model and the NJL model predict a mixed phase in the interior of the star.

Strange Star Equations of State Revisited

“…Actually, the radius can increase up to huge values if densities as low as 10 −15 fm −3 are considered. In order to plot this figure for the hadronic and hybrid stars, we choose the EOS derived in , 2004c, where the hybrid stars were obtained by the enforcement of Gibbs criterion for phase coexistence. In this case, the EOS is smooth and no discontinuities are present.…”

“…Strange matter is composed of deconfined quarks, including up, down, and strange quarks, plus the leptons necessary to ensure charge neutrality (Bodmer 1971;Witten 1984). This possibility arises because at the high densities present in the interior of neutron stars, a phase transition from hadronic to quark phase is possible (Glendenning 2000;Menezes & Providência 2003, 2004c. Approximately one-third of the quarks are strange quarks, with the exact fraction depending on the model used to describe the quark phase.…”

“…In hybrid stars low-density regions are composed of hadronic matter, but in high-density regions a deconfinement of the quarks from the hadrons occurs, leading to a quark phase. Many different EOS have been built, including EOS for the phase immediately after the formation of the neutron star when the neutrinos are still trapped (Panda et al 2004a; and for the subsequent (deleptonized) phase after the neutrinos escape (Menezes & Providência 2003, 2004cPanda et al 2004b).…”

On the anomalous mass defect of strange stars in the Field Correlator Method

“…Another well known model is the Nambu-Jona-Lasinio model [16,17] used to investigate quark matter properties in compact stars in Refs. [18,19]. It exhibits chiral symmetry breaking, but the quark confinement is not explicitly included.…”

Strange stars properties calculated in the framework of the Field Correlator Method

“…The current treatments have led to theoretical results which are unable to fully explain the observed phenomena of compact astrophysical objects. Among these treatments, the Nambu-Jona-Lasinio (NJL) model [1,2] and MIT Bag model [3] have been used in the study of compact stars to describe quark matter at nonzero temperature and density [4][5][6]. However, in both the NJL and MIT Bag models, quarks enter in the respective EOS as a free quark gas with Fermi-Dirac distribution.…”