A new quarkhadron hybrid equation of state for astrophysics. I. Highmass twin compact stars
Abstract
Aims: We present a new microscopic hadronquark hybrid equation of state model for astrophysical applications, from which compact hybrid star configurations are constructed. These are composed of a quark core and a hadronic shell with a firstorder phase transition at their interface. The resulting massradius relations are in accordance with the latest astrophysical constraints.
Methods: The quark matter description is based on a quantum chromodynamics (QCD) motivated chiral approach with higherorder quark interactions in the Dirac scalar and vector coupling channels. For hadronic matter we select a relativistic meanfield equation of state with densitydependent couplings. Since the nucleons are treated in the quasiparticle framework, an excluded volume correction has been included for the nuclear equation of state at suprasaturation density which takes into account the finite size of the nucleons.
Results: These novel aspects, excluded volume in the hadronic phase and the higherorder repulsive interactions in the quark phase, lead to a strong firstorder phase transition with large latent heat, i.e. the energydensity jump at the phase transition, which fulfils a criterion for a disconnected thirdfamily branch of compact stars in the massradius relationship. These twin stars appear at high masses (~2 M_{☉}) that are relevant for current observations of highmass pulsars.
Conclusions: This analysis offers a unique possibility by radius observations of compact stars to probe the QCD phase diagram at zero temperature and large chemical potential and even to support the existence of a critical point in the QCD phase diagram.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 May 2015
 DOI:
 10.1051/00046361/201425318
 arXiv:
 arXiv:1411.2856
 Bibcode:
 2015A&A...577A..40B
 Keywords:

 stars: neutron;
 stars: interiors;
 dense matter;
 equation of state;
 Astrophysics  High Energy Astrophysical Phenomena;
 High Energy Physics  Phenomenology;
 Nuclear Theory
 EPrint:
 Accepted for publication in Astron. &