Rotating neutron stars with quark cores

The rotating neutron-star properties are studied to investigate a phase transition to quark matter. The density-dependent relativistic mean-field model (DD-RMF) is employed to study the hadron matter, while the vector-enhanced bag (vBag) model is used to study the quark matter. The star-matter properties such as mass, radius, the moment of inertia, rotational frequency, Kerr parameter, and other important quantities are studied to see their effect on quark matter. The maximum mass of a rotating neutron star with the DD-LZ1 and DD-MEX parameter sets is found to be around 3M(circle dot) for pure hadronic phase and decreases to around 2.6M(circle dot) upon phase transitioning to quark matter, which satisfies the recent GW190814 possible maximum mass constraint, implying that the secondary component of GW190814 could be a fast-rotating hybrid star. For DDV, DDVT, and DDVTD parameter sets, the maximum mass decreases to satisfy 2M(circle dot). The moment of inertia calculated for various DD-RMF parameter sets decreases with the increasing mass satisfying constraints from various measurements. Other important quantities calculated also vary with the bag constant and hence show that the presence of quarks inside neutron stars can also allow us to constraint these quantities to determine a proper equation of state. Also, the theoretical study along with the accurate measurement of uniformly rotating neutron-star properties may offer some valuable information concerning the high-density part of the equation of state.