Hyperons, deconfinement and the speed of sound in neutron stars

Abstract

The effects of the presence of hyperons and a phase transition to deconfined quark matter on the speed of sound in neutron stars is investigated. For this purpose a composite description consisting of a model of the covariant field theory of hadrons and one for unbound quarks are used. A phase transition with continuous and monotonous variation of the equation of state is assumed. The predictions are contrasted with recent observational data on isolated neutron stars as well as on binary systems. Only one candidate is finally obtained from six different descriptions. According to the present calculations the onset of the hyperons causes the equilibrium speed of sound to exceed the conformal limit. Qualitative agreement with recent work about the influence of the speed of sound on the g-modes of oscillation in neutron stars is obtained.