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Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R ~ 8 km. PACS: 26.60+c, 21.65+f, 97.60.Gb, 97.60.Jd
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars is investigated. We find that the equation of state exhibits a second stable minimum at large hyperon contents which is in accord with existing hypernuclear data. This second solution gives rise to new effects for neutron star properties which are similar to the ones proposed for the deconfinement transition to strange quark matter and absolutely stable strange stars. We find that the corresponding hyperstars can have rather small radii of R=6-8 km independent of the mass. PACS: 26.60+c, 21.65+f, 97.60.Gb, 97.60.Jd
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated.We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R 8 km.
The effects of internal quark structure of baryons on the composition and structure of neutron star matter with hyperons are investigated in the quark- meson coupling (QMC) model. The QMC model is based on mean-field description of nonoverlapping spherical bags bound by self-consistent exchange of scalar and vector mesons. The predictions of this model are compared with quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear matter saturation properties. By employing a density dependent bag constant through direct coupling to the scalar field, the QMC model is found to exhibit identical properties as QHD near saturation density. Furthermore, this modified QMC model provides well-behaved and continuous solutions at high densities relevant to the core of neutron stars. Two additional strange mesons are introduced which couple only to the strange quark in the QMC model and to the hyperons in the QHD model. The constitution and structure of stars with hyperons in the QMC and QHD models reveal interesting di erences. This suggests the importance of quark structure e ects in the baryons at high densities. PACS number(s): 26.60.+c, 21.65.+f, 12.39.Ba, 24.85.+p
We study in detail the nuclear aspects of a neutron-star merger in which deconfinement to quark matter takes place. For this purpose, we make use of the Chiral Mean Field (CMF) model, an effective relativistic model that includes self-consistent chiral symmetry restoration and deconfinement to quark matter and, for this reason, predicts the existence of different degrees of freedom depending on the local density/chemical potential and temperature. We then use the out-of-chemical-equilibrium finite-temperature CMF equation of state in full general-relativistic simulations to analyze which regions of different QCD phase diagrams are probed and which conditions, such as strangeness and entropy, are generated when a strong first-order phase transition appears. We also investigate the amount of electrons present in different stages of the merger and discuss how far from chemical equilibrium they can be and, finally, draw some comparisons with matter created in supernova explosions and heavy-ion collisions.
We study properties of compact stars with the deconfinement phase transition in their interiors. The equation of state of cold baryon-rich matter is constructed by combining a relativistic mean-field model for the hadronic phase and the MIT Bag model for the deconfined phase. In a narrow parameter range two sequences of compact stars (twin stars), which differ by the size of the quark core, have been found. We demonstrate the possibility of a rapid transition between the twin stars with the energy release of about 10 ^52 ergs. This transition should be accompanied by the prompt neutrino burst and the delayed gamma-ray burst.
We study properties of compact stars with the deconfinement phase transition in their interiors. The equation of state of cold baryon-rich matter is constructed by combining a relativistic mean-field model for the hadronic phase and the MIT Bag model for the deconfined phase. In a narrow parameter range two sequences of compact stars (twin stars), which differ by the size of the quark core, have been found. We demonstrate the possibility of a rapid transition between the twin stars with the energy release of about 1052 ergs. This transition should be accompanied by the prompt neutrino burst and the delayed gamma-ray burst.
We investigate various properties of neutron star matter within an e ective chiral SU(3)L × SU(3)R model. The predictions of this model are compared with a Walecka-type model. It is demonstrated that the importance of hy- peron degrees are strongly depending on the interaction used, even if the equation of state near saturation density is nearly the same in both models. While the Walecka-type model predicts a strange star core with strangeness fraction fS 4/3, the chiral model allows only for fS 1/3 and predicts that 0, + and 0 will not exist in star, in contrast to the Walecka-type model. PACS: 26.60+c, 21.65+f, 24.10Jv
n this article we will focus on the appearance of the hadron-quark phase transition and the formation of strange matter in the interior region of the hypermassive neutron star and its conjunction with the spectral properties of the emitted gravitational waves (GWs). A strong hadron-quark phase transition might give rise to a mass-radius relation with a twin star shape and we will show in this article that a twin star collapse followed by a twin star oscillation is feasible. If such a twin star collapse would happen during the postmerger phase it will be imprinted in the GW-signal.
Hypermassive hybrid stars (HMHS) are extreme astrophysical objects that could be produced in the merger of a binary system of compact stars. In contrast to their purely hadronic counterparts, hypermassive neutron stars (HMNS), these highly differentially rotating objects contain deconfined strange quark matter in their slowly rotating inner region. HMHS and HMNS are both mestastable configurations and can survive only shortly after the merger before collapsing to rotating black holes. The appearance of the phase transition from hadronic to quark matter in the interior region of the HMHS and its conjunction with the emitted GW will be addressed in this article by focussing on a specific case study of the delayed phase-transition scenario that takes place during the post-merger evolution of the remnant. The complicated dynamics of the collapse from the HMNS to the more compact HMHS will be analysed in detail. In particular, we will show that the interplay between the spatial density/temperature distributions and the rotational profiles in the interior of the wobbling HMHS after the collapse generates a high-temperature shell within the hadron-quark mixed phase region of the remnant.