Signals of the QCD Phase Transition in Core-Collapse Supernovae

Abstract

We explore the implications of the QCD phase transition during the postbounce evolution of corecollapse supernovae. Using the MIT bag model for the description of quark matter and assuming small bag constants, we find that the phase transition occurs during the early postbounce accretion phase. This stage of the evolution can be simulated with general relativistic three-flavor Boltzmann neutrino transport. The phase transition produces a second shock wave that triggers a delayed supernova explosion. If such a phase transition happens in a future galactic supernova, its existence and properties should become observable as a second peak in the neutrino signal that is accompanied by significant changes in the energy of the emitted neutrinos. In contrast to the first neutronization burst, this second neutrino burst is dominated by the emission of anti-neutrinos because the electrondegeneracy is lifted when the second shock passes through the previously neutronized matter. In search of the phase transition from hadronic to deconfined matter, heavy ion experiments at RHIC and at LHC at CERN explore the QCD phase diagram for large temperatures and small baryochemical potentials. For these conditions, which were also present in the early universe, lattice QCD calculations predict a crossover transition between the deconfined chirally symmetric phase and the confined phase with broken chiral symmetry. For high chemical potentials and low temperatures a first order chiral phase transition is expected and will be tested at the FAIR facility at GSI Darmstadt.Due to their large central densities, compact stars can also serve as laboratories for nuclear matter beyond saturation density and may contain quark matter [1]. The formation of quark matter in compact stars is mainly discussed in two scenarios, in protoneutron stars (PNS) after the supernova explosion [2] and in old accreting neutron stars [3,4]. For the first case, deleptonization leads to the loss of lepton pressure and therefore to an increase in the central density so that the phase transition takes place. Possible observables are the emission of gravitational waves [3,4] due to the contraction of the neutron star or delayed γ-ray bursts [5].In this article we want to follow a third and less discussed case. The phase transition from hadronic to quark matter can already occur in the early postbounce phase of a core-collapse supernova [6,7,8,9,10]. This requires a phase transition onset close to saturation density, which can be realized for high temperatures and low proton fractions. For such a scenario Ref. [8] found the formation of a second shock as a direct consequence of the phase transition. However, the lack of neutrino transport in their model allowed them to investigate the dynamics only for a few ms after bounce. Very recently, a quark matter phase transition has been considered with Boltzmann neutrino transport for a 100 M ⊙ progenitor [11]. The appearance of quark matter shortened the time until black hole formation due to the softening of the equation o...

A new quark-hadron hybrid equation of state for astrophysics

“…Pons et al 2001;Popov et al 2006;Blaschke et al 2013b) and simulations of core-collapse supernovae (cf. Sagert et al 2009;Fischer et al 2011;Nakazato et al 2014). It is therefore of paramount interest to develop quark-hadron hybrid models from which it is possible to deduce observables that allow us to further constrain the as yet highly uncertain QCD phase diagram, e.g.…”

Soft nuclear equation-of-state from heavy-ion data and implications for compact stars

“…At these densities, hyperons, kaons, and quarks, if they appear at all, should not play a dominant role [46]. However, their possible appearance in a first order phase transition could be probed in the neutrino signal of a galactic supernova explosion [47,48]. In Fig.…”

Neutrino and Gravitational-Wave Signatures of Quark Stars

“…Several groups have previously studied the possibility of forming a quark core in CCSNe [9][10][11]. These studies typically make use of spherically symmetric general relativistic radiation hydrodynamics and Boltzmann neutrino transport.…”

“…The nuclear matter equation of state (EOS) is modified to include a quark phase -a hybrid EOS such as the combination of HShen and Bag Model EOS's. For example, it was reported that for a progenitor mass of 10.8 M⊙ and Bag constant B 1/4 = 162 MeV, the quark phase transition occurs at relatively low density, resulting in a second collapse of the core triggering a delayed shock, at hundreds of ms after the prompt collapse [10,11].…”