Quark Matter in Compact Stars: Astrophysical Implications and Possible Signatures (original) (raw)
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Nuclear Physics A, 2003
In a theoretical interpretation of observational data from the neutron star EXO 0748-676,Özel concluded that quark matter probably does not exist in the center of neutron stars [1]. However, this conclusion was based on a limited set of possible equations of state (EoS) for quark matter. Here we compareÖzel's observational limits with predictions based on a more comprehensive set of proposed quark matter equations of state from the existing literature, and conclude that the presence of quark matter in EXO 0748-676 is not ruled out.
Quark Deconfinement and Implications for the Radius and the Limiting Mass of Compact Stars
The Astrophysical Journal, 2004
We study the consequences of the hadron-quark deconfinement phase transition in stellar compact objects when finite size effects between the deconfined quark phase and the hadronic phase are taken into account. We show that above a threshold value of the central pressure (gravitational mass) a neutron star is metastable to the decay (conversion) to a hybrid neutron star or to a strange star. The mean-life time of the metastable configuration dramatically depends on the value of the stellar central pressure. We explore the consequences of the metastability of "massive" neutron stars and of the existence of stable compact quark stars (hybrid neutron stars or strange stars) on the concept of limiting mass of compact stars. We discuss the implications of our scenario on the interpretation of the stellar mass and radius extracted from the spectra of several X-ray compact sources. Finally, we show that our scenario implies, as a natural consequence a two step-process which is able to explain the inferred "delayed" connection between supernova explosions and GRBs, giving also the correct energy to power GRBs.
Quark Matter in Neutron Stars: An Aperçu
Modern Physics Letters A, 2006
The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.
Quark matter nucleation in neutron stars and astrophysical implications
The European Physical Journal A, 2016
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 (T = 0) and hot β-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 10 53 erg, 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 M cr for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M < M cr could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.
Metastable strange matter and compact quark stars
Journal of Physics G: Nuclear and Particle Physics, 2003
Strange quark matter in beta equilibrium at high densities is studied in a quark confinement model. Two equations of state are dynamically generated for the same set of model parameters used to describe the nucleon: one corresponds to a chiral restored phase with almost massless quarks and the other to a chiral broken phase. The chiral symmetric phase saturates at around five times the nuclear matter density. Using the equation of state for this phase, compact bare quark stars are obtained with radii and masses in the ranges R ∼ 5 − 8 km and M ∼ M ⊙. The energy per baryon number decreases very slowly from the center of the star to the periphery, remaining above the corresponding values for the iron or the nuclear matter, even at the edge. Our results point out that strange quark matter at very high densities may not be absolutely stable and the existence of an energy barrier between the two phases may prevent the compact quarks stars to decay to hybrid stars.
Quark matter in light neutron stars
Physical Review D, 2020
Higher-order repulsive interactions are included in the three-flavor NJL model in order to describe the quark phase of an hybrid star. The effect of 4-quark and 8-quark vector-isoscalar interactions in the stability of hybrid star configurations is analyzed. The presence of a 8-quark vector-isoscalar channel is seen to be crucial in generating large quark branches in the M (R) diagram. This is due to its stiffening effect on the quark matter equation of state which arises from the non-linear density dependence of the speed of sound. This additional interaction channel allows for the appearance of a quark core at moderately low NS masses, ∼ 1M , and provides the required repulsion to preserve the star stability up to ∼ 2.1M. Furthermore, we show that both the heaviest NS mass generated, Mmax, and its radii, Rmax, are quite sensitive to the strength of 8-quark vector-isoscalar channel, leading to a considerable decrease of Rmax as the coupling increases. This behavior imprints a considerable deviation from the purely hadronic matter equation of state in the Λ(M) diagram, which might be a possible signature of the quark matter existence, even for moderately low NS masses, ∼ 1.4 M. The resulting M (R) and Λ(R) relations are in accordance with the latest astrophysical constraints from NICER and Ligo/VIRGO observations, respectively.
Astrophysics of dense quark matter in compact stars
2009
Massive neutron stars may harbor deconfined quark matter in their cores. I review some recent work on the microphysics and the phenomenology of compact stars with cores made of quark matter. This includes the equilibrium and stability of non-rotating and rapidly rotating stars, gravitational radiation from deformations in their quark cores, neutrino radiation and dichotomy of fast and slow cooling, and pulsar radio-timing anomalies.
EMMI rapid reaction task force meeting on quark matter in compact stars
Journal of Physics G: Nuclear and Particle Physics, 2014
The recent measurement of two solar mass pulsars has initiated an intense discussion on its impact on our understanding of the high-density matter in the cores of neutron stars. A task force meeting was held from October 7-10, 2013 at the Frankfurt Institute for Advanced Studies to address the presence of quark matter in these massive stars. During this meeting, the recent observational astrophysical data and heavy-ion data was reviewed. The possibility of pure quark stars, hybrid stars and the nature of the QCD phase transition were discussed and their observational signals delineated.