Eur. Phys. J. A (2016) 52: 58
https://doi.org/10.1140/epja/i2016-16058-5

Review

Quark matter nucleation in neutron stars and astrophysical implications

¹ Dipartimento di Fisica “E. Fermi”, Università di Pisa, Largo B. Pontecorvo, 3, I-56127, Pisa, Italy
² INFN, Largo B. Pontecorvo, 3, I-56127, Pisa, Italy
³ European Gravitational Observatory, Via E. Amaldi, I-56021, Cascina, Italy
⁴ CFisUC, Department of Physics, University of Coimbra, PT-3004-516, Coimbra, Portugal

^* e-mail: ignazio.bombaci@unipi.it

Received: 2 October 2015
Accepted: 14 December 2015
Published online: 18 March 2016

Abstract

A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We investigate the quark deconfinement phase transition in cold ( and hot -stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates an enormous amount of energy, of the order of 10⁵³erg, which causes a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the Universe two coexisting families of compact stars: pure hadronic stars and quark stars. We introduce the concept of critical mass for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.