1,720,992 research outputs found
Two-meson exchange hyperonic three-body forces and consequences for neutron stars
No full textWe construct two-meson exchange three-baryon potentials between two nucleons and one hyperon (NNY) consistent with the two body nucleon-hyperon (NY) J04 potential of the Jülich group. In particular, we focus on the NNΛ and N Nσ - forces since Λ and σ - are the first hyperons expected to appear in microscopic calculations of neutron star matter. Brueckner-Hartree-Fock calculations of the hyperonic matter are then performed including the effect of these three-body forces. Our results show that at high densities the total contribution of the NNY force is repulsive making the resulting equation of state stiffer, as required from neutron star mass observations. © 2013 Elsevier B.V
Formation of hybrid stars from metastable hadronic stars
No full textWe study the consequences of quark matter nucleation in cold hadronic matter employing three relativistic-mean-field models to describe the hadronic phase and the Nambu-Jona-Lasinio (NJL) model for the quark one. We explore the effect of a vector interaction in the NJL Lagrangian and of a phenomenological bag constant on neutron stars metastability. We delineate the region of parameters of the quark phase that allow for the formation of stable hybrid stars with mass compatible with the almost 2MâŠTM pulsars PSR J1614-2230 (1.97±0.04MâŠTM) and PSR J0348+0432 (2.01±0.04MâŠTM). It is shown, however, that not all hybrid star configurations with ∼2M ŠTM are populated after nucleation. © 2013 American Physical Society
Chiral model approach to quark matter nucleation in neutron stars
No full textThe nucleation process of quark matter in both cold and hot dense hadronic matter is investigated using a chiral approach to describe the quark phase. We use the Nambu-Jona-Lasinio and the chromo dielectric models to describe the deconfined phase and the nonlinear Walecka model for the hadronic one. The effect of hyperons on the transition phase between hadronic and quark matter is studied. The consequences of the nucleation process for neutron star physics are outlined
Evolution of proto-neutron stars with hadron-quark phase transition
No full textWe investigate the consequences of the quark deconfinement phase transition on the evolution of proto-neutron stars. Assuming a first order phase transition, we calculate the nucleation time due to thermal and quantum nucleation mechanisms. We introduce the concepts of critical mass Mcr and limiting conversion temperature for proto-hadronic stars. We show that proto-hadronic stars with a mass M < Mcr could survive the early stages of their evolution without decaying to quark stars
Quark matter nucleation with a microscopic hadronic equation of state
No full textThe nucleation process of quark matter in cold (T = 0) stellar matter is investigated using the microscopic Brueckner-Hartree-Fock approach to describe the hadronic phase and using the MIT bag model, the Nambu-Jona-Lasinio, and the chromodielectric models to describe the deconfined phase of quark matter. The consequences of the nucleation process for neutron star physics are outlined. Hyperonic stars are metastable only for some of the quark matter equations of state considered. The effect of a hyperonic three-body force on the metastability of compact stars is estimated, and it is shown that, except for the Nambu-Jona-Lasinio model and the MIT bag model with a large bag pressure, the other models predict the formation of hybrid stars with a maximum mass not larger than similar to 1.62 M-circle dot
Metastability of hadronic compact stars
No full textPure hadronic compact stars, above a threshold value of their gravitational mass (central pressure), are metastable to the conversion to quark stars (hybrid or strange stars). In this paper, we present a systematic study of the metastability of pure hadronic compact stars using different relativistic models for the equation of state. In particular, we compare results for the quark-meson coupling model with those for the Glendenning-Moszkowski parametrization of the nonlinear Walecka model. For the quark-meson coupling model, we find large values (M(cr)=1.6-1.9M) for the critical mass of the hadronic star sequence and we find that the formation of a quark star is only possible with a soft quark matter equation of state. For the Glendenning-Moszkowski parametrization of the nonlinear Walecka model, we explore the effect of different hyperon couplings on the critical mass and on the stellar conversion energy. We find that increasing the value of the hyperon coupling constants shifts the bulk transition point for quark deconfinement to higher densities, increases the stellar metastability threshold mass and the value of the critical mass, and thus makes the formation of quark stars less likely. For the largest values of the hyperon couplings we find a critical mass which may be as high as 1.9-2.1M. These stellar configurations, which contain a large central hyperon fraction (f(Y,cr) similar to 30%), would be able to describe highly massive compact stars, such as the one associated with the millisecond pulsar PSR B1516 + 02B with a mass M = 1.94(-0.19)(+0.17)M(circle dot)
Nucleation of Quark Matter in Proto-Neutron Stars
No full textWe investigate the consequences of the quark deconfinement phase transition on the evolution of proto-neutron stars. Assuming a first order phase transition, we calculate the nucleation time due to thermal and quantum nucleation mechanisms. We introduce the concepts of critical mass M(cr) and limiting conversion temperature for proto-hadronic stars. We show that proto-hadronic stars with a mass M < M(cr) could survive the early stages of their evolution without decaying to quark stars
Estimation of the effect of hyperonic three-body forces on the maximum mass of neutron stars
No full textA model based on a microscopic Brueckner-Hartree-Fock approach of hyperonic matter supplemented with additional simple phenomenological density-dependent contact terms is employed to estimate the effect of hyperonic three-body forces on the maximum mass of neutron stars. Our results show that although hyperonic three-body forces can reconcile the maximum mass of hyperonic stars with the current limit of 1.4-1.5M(circle dot), they are unable to provide the repulsion needed to make the maximum mass compatible with the observation of massive neutron stars, such as the recent measurements of the unusually high masses of the millisecond pulsars PSR J1614-2230 (1.97 +/- 0.04M(circle dot)) and PSR J1903+0327 (1.667 +/- 0.021M(circle dot))
Evolution of newborn neutron stars: role of quark matter nucleation
No full textA phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We study the quark deconfinement phase transition in cold (T = 0) and hot beta-stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) is metastable to the conversion to a quark star (QS) (i.e. hybrid star or strange star). 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
Effects of quark matter nucleation on the evolution of proto-neutron stars
No full textContext. A phase of strong interacting matter with deconfined quarks is expected in the core of a massive neutron star. If this deconfinement phase transition is of the first order, as suggested by many models inspired by quantum chromodynamics, then it will be triggered by the nucleation of a critical size drop of the (stable) quark phase in the metastable hadronic phase. Within these circumstances it has been shown that cold (T = 0) pure hadronic compact stars above a threshold value of their gravitational mass (central pressure) are metastable with respect to the "decay" (conversion) to quark stars (i.e., compact stars made at least in part of quark matter). This stellar conversion process liberates a huge amount of energy (a few 10(53) erg), and it could be the energy source of some of the long gamma ray bursts.
Aims. The main goal of the present work is to establish whether a newborn hadronic star (proto-hadronic star) could survive the early stages of its evolution without "decaying" to a quark star. To this aim, we study the nucleation process of quark matter in hot (T not equal 0) beta-stable hadronic matter, with and without trapped neutrinos, using a finite temperature equation of state (EOS) for hadronic and quark matter.
Methods. The finite-temperature EOS for the hadronic and for the quark phases were calculated using the nonlinear Walecka model and the MIT bag model, respectively. The quantum nucleation rate was calculated making use of the Lifshitz & Kagan nucleation theory. The thermal nucleation rate was calculated using the Langer nucleation theory.
Results. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences of quark matter nucleation for the physics and the evolution of proto-neutron stars. We introduce the new concept of limiting conversion temperature and critical mass M-cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M < M-cr could survive the early stages of their evolution without decaying to a quark star. We extend the concept of maximum mass of a "neutron star" with respect to the classical one introduced by Oppenheimer & Volkoff to account for the existence of two distinct families of compact stars (hadronic stars and quark stars) as predicted by the present scenario
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