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Aims: We present a new microscopic hadron-quark hybrid equation of statemodel for astrophysical applications, from which compact hybrid starconfigurations are constructed. These are composed of a quark core and ahadronic shell with a first-order phase transition at their interface. Theresulting mass-radius relations are in accordance with the latest astrophysicalconstraints. Methods: The quark matter description is based on a quantumchromodynamics (QCD) motivated chiral approach with higher-order quarkinteractions in the Dirac scalar and vector coupling channels. For hadronicmatter we select a relativistic mean-field equation of state withdensity-dependent couplings. Since the nucleons are treated in thequasi-particle framework, an excluded volume correction has been included forthe nuclear equation of state at suprasaturation density which takes intoaccount the finite size of the nucleons. Results: These novel aspects, excludedvolume in the hadronic phase and the higher-order repulsive interactions in thequark phase, lead to a strong first-order phase transition with large latentheat, i.e. the energy-density jump at the phase transition, which fulfils acriterion for a disconnected third-family branch of compact stars in themass-radius relationship. These twin stars appear at high masses ($\sim$ 2M$_\odot$) that are relevant for current observations of high-mass pulsars.Conclusions: This analysis offers a unique possibility by radius observationsof compact stars to probe the QCD phase diagram at zero temperature and largechemical potential and even to support the existence of a critical point in theQCD phase diagram.

A new quark-hadron hybrid equation of state for astrophysics - I. High-mass twin compact stars