Hadron-quark deconfinement phase transition in hybrid stars

Abstract

Astronomical statistics shows that the mass of neutron star is of the order of the solar mass, but the radius is only about ten kilometers. Therefore, the neutron star is highly condensed and there may be a variety of competing material phases inside the compact star. Hadron-quark deconfinement phase transition that is poorly understood at high density can be studied by the matter properties of hybrid star. The hybrid star contains many kinds of material phases, which cannot be described uniformly by one theory. So, different material phases are described by different theories. The hadronic phase is described by the relativistic mean-field theory with parameter set FSUGold including <i>ω</i><sup>2</sup><i>ρ</i><sup>2</sup> interaction term, and the quark phase is described by an effective mass bag model in which the quark mass is density-dependent. The hadron-quark mixed phase is constructed by the Gibbs phase transition, and the properties of hybrid star in <i>β</i> equilibrium is studied in this model. It is found that the bag constant <i>B</i> has a great influence on the starting point and ending point of the hadron-quark deconfinement phase transition and the particle composition in the hybrid star. Comparing with the starting point of phase transition, the influence of <i>B</i> on the ending point of phase transition is very obvious. For the hybrid star, the equation of state of matter becomes stiffer at low density and softer at high density as <i>B</i> increases. The overall effect is that the slope of the mass-radius curve increases with <i>B</i> increasing. The calculated results show that the maximum mass of hybrid star is between 1.3 solar mass and 1.4 solar mass (<i>M</i><sub>☉</sub>), and the radius is between 9 km and 12 km. In addition, the influence of attractive and repulsive <i>Σ</i> potential on the properties of hybrid stars are studied. The results show that the <i>Σ</i> potential has a great influence on the particle composition in the hybrid star. We also find that the repulsive <i>Σ</i> potential makes the hybrid star have a greater maximum mass then an attractive <i>Σ</i> potential. For the attractive <i>Σ</i> potential, the maximum mass of hybrid star is 1.38<i>M</i><sub>☉</sub>, while for the repulsive <i>Σ</i> potential, the maximum mass of hybrid stars is 1.41<i>M</i><sub>☉</sub>.