Beyond the Hadronic Limit: Neutron Star Maximum Mass as a QCD Phase Regime Threshold and Implications for Black Hole Structure

Abstract "The Neutron Star–Black Hole Boundary as a Phase Transition of Strongly Interacting Matter" Recent observationally constrained studies of neutron star equations of state indicate that as stellar mass approaches its maximum stable value, purely hadronic descriptions become increasingly inadequate. Bayesian analyses (Annala et al. 2020, 2023) show that the probability of deconfined quark matter cores rises significantly in the most massive neutron stars. Independent hybrid TOV models further demonstrate that the size and mass fraction of quark matter cores increase monotonically with total stellar mass.These converging results suggest that the neutron star maximum mass is not merely a gravitational instability threshold, but may correspond to a regime in which hadronic matter ceases to be the dominant coherent phase of strongly interacting matter.By drawing a parallel with the QCD phase structure known from early-universe cosmology, we explore the hypothesis that the neutron star–black hole boundary represents a transition into a strongly deconfined regime. Within this framework, black holes may be interpreted not as singular anomalies, but as extreme-density phase configurations of matter and field.We further discuss how such a regime could dynamically favor stratified structures consistent with electron-dominated external plasma behavior, as described in the Multibolla model.