Properties of the mixed phase core in maximum mass neutron stars

In the context of observed massive neutron stars (NSs), we examine the internal structure, phase transitions, and the impacts of the equation of state (EOS) in maximum NSs. We investigate the stiffness changes in the EOS during the hadron-quark phase transition within the NSs. The relativistic mean-field (RMF) model and RMF model with a density-dependent isovector coupling, known as the RMFL model, are used to describe hadronic matter, while to the represent quark matter, the Nambu-Jona-Lasinio (NJL) model is applied. We explore the strength of vector coupling in quark matter, which delayed the onset density and reduced the maximum mass of NS, but does not exhibit a clear correlation with the NS central density. A considerable size of the mixed phase core could exist in the maximum mass NS but with corresponding small mixed phase mass.