HESS J1731-347 and the existence of exotic matter: Kaon condensation in neutron stars

¹ Department of Physics, Faculty of Science, University of Zagreb, Bijenicˇka cesta 32, 10000 Zagreb, Croatia
² Department of Theoretical Physics, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
³ Institute of Experimental and Applied Physics, Czech Technical University, Prague, 110 00, Czechia

^* e-mail: pkoliogi@auth.gr

Published online: 8 October 2024

Abstract

The recent observation of a compact star with the lowest observable mass of 0.77^{+0.20 –0.17} M_⊙ within the supernova remnant HESS J1731-347 has redefined our understanding for the dense nuclear matter equation of state and enhances the existence of exotic matter. In the present work, we investigate the possible existence of kaon condensation in hadronic neutron stars through the framework of the Momentum-Dependent Interaction nuclear model describing the dense nuclear matter. We concentrate on the strangeness content of the proton and its implications on both the microscopic and macroscopic properties of neutron stars. The aforementioned quantity is of interest as it is also directly related to the location of the phase transition to kaons. The simultaneous description of the compact object within the HESS J1731-347 and the maximum observable neutron star mass imposes severe constraints on the strangeness content of the proton and the critical density for kaon condensation. The present study along with observations of neutron stars, may help to provide tighter constraints on the equation of state of dense nuclear matter and, even more, to shed light to the existence of an exotic core in neutron stars.