Eur. Phys. J. A (2016) 52: 232
https://doi.org/10.1140/epja/i2016-16232-9

Regular Article - Theoretical Physics

Neutron star mass limit at 2M_⊙ supports the existence of a CEP

¹ Bogoliubov Laboratory of Theoretical Physics, JINR Dubna, Dubna, Russia
² Department of Physics, University of Zagreb, Zagreb, Croatia
³ National Research Nuclear University (MEPhI), Moscow, Russia
⁴ Institute of Theoretical Physics, University of Wroclaw, Wroclaw, Poland
⁵ Department of Physics and Astronomy, University of Tennessee, 37996, Knoxville, TN, USA
⁶ Physics Division, Oak Ridge National Laboratory, 37831, Oak Ridge, TN, USA
⁷ GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany

^* e-mail: alvarez@theor.jinr.ru

Received: 20 July 2015
Accepted: 25 July 2016
Published online: 19 August 2016

Abstract

We point out that the very existence of a “horizontal branch” in the mass-radius characteristics for neutron stars indicates a strong first-order phase transition and thus supports the existence of a critical endpoint (CEP) of first-order phase transitions in the QCD phase diagram. This branch would sample a sequence of hybrid stars with quark matter core, leading to the endpoint of stable compact star configurations with the highest possible baryon densities. Since we know of the existence of compact stars with , this hypothetical branch has to lie in the vicinity of this mass value, if it exists. We report here a correlation between the maximal radius of the horizontal branch and the pressure at the onset of hadron-to-quark matter phase transition, which is likely to be a universal quantity of utmost relevance to the upcoming experiments with heavy-ion collisions at NICA and FAIR.