Metastable strange matter and compact quark stars.pdf

a r X i v : a s t r o - p h / 0 3 0 4 0 9 6 v 1 4 A p r 2 0 0 3 Metastable strange matter and compact quark stars M. Malheiro? ?, M. Fiolhais§ and A. R. Taurines? ? Instituto de F??sica, Universidade Federal Fluminense, 24210-340 Nitero?i, Brazil § Departamento de F??sica and Centro de F??sica Computacional, Universidade de Coimbra, P-3004-516 Coimbra, Portugal ? Instituto de F??sica, Universidade Federal do Rio Grande do Sul CP 15051, 91501-970 Porto Alegre, Brazil 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 center of the star to the periphery, remaining above the corresponding values for the iron or the 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 quarks stars to decay to hybrid stars. Submitted to: J. Phys. G: Nucl. Phys. ? Email: mane@if.uff.br Metastable strange matter and compact quark stars 2 1. Introduction The recent discoveries of X-ray sources, whose origin may be attributed to strange stars [1, 2, 3], is stimulating theoretical research on the structure, composition, dynamics and evolution of such objects. It is believed that the innermost region of compact stars, such as neutron stars, can be made out of hyperons, meson condensates or quark matter [4, 5, 6, 7, 8], whose thermodynamical behavior can be expr