Constraining twin stars with cold neutron star cooling data

Abstract

We investigate the influence of a phase transition from hadronic matter to a deconfined quark phase inside a neutron star on its cooling behavior including the appearance of twin star solutions in the mass-radius diagram. We find that while the inferred neutrino luminosity of cold transiently accreting star in MXB 1659-29 is reproduced in all of the constructed twin star models, the luminosity of a colder source, the neutron star in SAX J1808.4-3658, cannot be described by equations of state with quark-hadron transition densities below 1.7 saturation density, suggesting that twin stars with such low density transitions to the quark phase are not realized in nature. We also discuss how constraints to the quark-hadron phase transition density are strongly dependent on the cooling effectiveness of neutrino reactions in the quark phase. Published by the American Physical Society 2025