A phenomenological study of hybrid stars in which the crossover transition from quark to hadron makes the EOS stiffer in contrast to the hybrid EOS based on Maxwell condition

In this paper, we make a phenomenological study of the mass–radii relationship of hybrid stars from the point of view of the smooth crossover phase transition. We find a way to construct stiff hybrid equations of state (EOSs) with soft EOSs of both the quark matter and the hadronic matter. For the hadron phase, we adopt the EOS softened by introducing hyperons that are considered to exist in the core of a neutron star. For the quark phase, we introduce a quark EOS based on the Dyson–Schwinger equation (DSE) that is calculated in our previous work, and it is also a soft EOS. In contrast to the hybrid EOS based on Maxwell condition, we find that the resulting EOS is stiff and the maximum mass of the hybrid stars is still about two times of solar mass. This result indicates the rich possibilities of the crossover model.