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The possibility of quark deconfinement in the interiors of neutron stars is investigated within the physics-informed Bayesian analysis of the observational data on neutron stars, which allows for distinguishing between the scenarios with quark cores and without them [1]. For this the recently proposed three-flavor nonlocal NJL model of quark matter with the scalar attractive, vector repulsive and diquark pairing interaction channels is used to construct a large set of asymptotically conformal hybrid quark-hadron equations of state with CFL color superconductivity [2]. Independent of the analyzed set of observational data the most probable hybrid equations of state are statistically preferred over the purely hadronic baseline on the level of one-two orders of magnitude. This suggests that quark cores may exist in all observed neutron stars with the most probable onset density below 1.5 saturation densities and the onset mass well below one solar mass. Such small values are explained using a simple model of quark confinement, which shows that the onset density of deconfinement strongly depends on isospin asymmetry: in symmetric matter it is at least three times larger than in neutron stars [3]. This answers the question why in neutron stars deconfinement occurs at rather small densities, while under the conditions of heavy ion collisions its traces are not reliably detected up to the highest densities of the proton flow data of Denielewicz et al. [4].
[1] A. Ayriyan, O. Ivanytskyi, D. Blaschke, arXiv:2509.02554 [nucl-th] (2025).
[2] O. Ivanytskyi, Phys.Rev.D 111, 3 (2025).
[3] P. Panasiuk, O. Ivanytskyi, V. Sagun, D. Blaschke, A. Ayriyan, inpreparation (2026).
[4] P. Danielewicz, R. Lacey and W. G. Lynch, Science 298, 1593 (2002).
