Unified Interacting Quark Matter and its Astrophysical Implications

We investigate interacting quark matter (IQM), including the perturbative QCD correction and color superconductivity, for both up-down quark matter ($ud$QM) and strange quark matter (SQM). We first derive an equation of state (EOS) unifying all cases by a simple reparametrization and rescaling, through which we manage to maximally reduce the number of degrees of freedom. We find, in contrast to the conventional EOS $p=1/3(\rho-4B_{\rm eff})$ for non-interacting quark matter, that taking the extreme strongly interacting limit on the unified IQM EOS gives $p=\rho-2B_{\rm eff}$, where $B_{\rm eff}$ is the effective bag constant. We employ the unified EOS to explore the properties of pure interacting quark stars (IQSs) composed of IQM. We describe how recent astrophysical observations, such as the pulsar-mass measurements, the NICER analysis, and the binary merger gravitational-wave events GW170817, GW190425, and GW190814, further constrain the parameter space. An upper bound for the maximum allowed mass of IQSs is found to be $M_{\rm TOV}\lesssim 3.23 M_{\odot}$. Our analysis indicates a new possibility that the currently observed compact stars, including the recently reported GW190814's secondary component ($M=2.59^{+0.08}_{-0.09}\, M_{\odot}$), can be quark stars composed of interacting quark matter.