Metastable strange matter and compact quark stars

Abstract

Strange quark matter in beta equilibrium at high densities is studied in a quark confinement model. Two equations of state are dynamically generated for the same set of model parameters used to describe the nucleon: one corresponds to a chiral restored phase with almost massless quarks and the other to a chiral broken phase. The chiral symmetric phase saturates at around five times the nuclear matter density. Using the equation of state for this phase, compact bare quark stars are obtained with radii and masses in the ranges R ∼ 5–8 km and M ∼ M⊙. The energy per baryon number decreases very slowly from the centre of the star to the periphery, remaining above the corresponding values for iron or nuclear matter, even at the edge. Our results point out that strange quark matter at very high densities may not be absolutely stable and the existence of an energy barrier between the two phases may prevent the compact quark stars from decaying to hybrid stars.