A complementary way to investigate the Hadron-Quark-Gluon Phase transition in heavy ion collisions is to analyze properties of dense astrophysical objects, i.e. neutron stars. A neutron star can be simply described as a giant nucleus. However, due to the enormous gravitational contraction, it can reach densities up to several times the density found in the Pb nucleus. This property allows the formation of a core made up of free quarks and gluons. Once this new phase is formed, the new state drastically changes the neutron star macroscopic properties, such as its mass and radius. In the present work, we follow a route opposite to the common sense, investigating the properties of the phase transition by analyzing neutron star properties of mass and radius. This observations can determine the density where the transition can occur or the order of the transition using some sort of reverse engineering. As a consequence, the values of the bag constant or the strong coupling constant can be inferred.

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We analyze the implications of quantum hadrodynamics (QHD) and quantum chromodynamics (QCD) to model, respectively, two distinct phases of nuclear matter, a baryon–meson phase and a quark–gluon phase. We develop an equation of state (EoS) in the framework of a quark–meson coupling model for the hadron–meson phase using a new version of the fuzzy bag model with scalar–isoscalar, vector–isoscalar and vector–isovector meson–quark couplings and leptonic degrees of freedom as well as the constrains from chemical equilibrium, baryon number and electric charge conservation. We model the EoS for the QGP phase for asymptotically free massless quarks and gluons using the MIT approach and a temperature and baryon chemical potential dependent bag constant, B(T,μ), which allows an isentropic equilibrium phase transition from a QGP to a hadron gas as determined by thermodynamics. Our predictions yield the EoS and static global properties of neutron stars and protoneutron stars at low and moderate values of temperature. Our results are slightly modified in comparison to predictions based on the standard MIT bag model with a constant bag pressure B.

We study two distinct phases of nuclear matter, a baryon-meson phase and a quarkgluon phase (QGP). For the baryon-meson phase we develop an equation of state (EoS) using a quark-meson formulation based on a new version of the fuzzy bag model with scalar-isoscalar, vector-isoscalar and vector-isovector meson-quark couplings and leptonic degrees of freedom as well as the constraints of chemical equilibrium, baryon number and electric charge conservation. For the QGP phase we model an EoS for asymptotically free massless quarks and gluons using the MIT approach and a temperature and baryon chemical potential dependent bag constant, B(T, µ), which allows an isentropic equilibrium phase transition from a QGP to a hadron gas. Our main results indicate the EoS and static global properties of neutron stars and protoneutron stars at low and moderate values of temperature are slightly modified in comparison to the predictions based on the MIT bag model with a constant B.