We used the equations of state of dense nuclear matter to construct the macroscopic properties of neutron stars and test them using available observational results. The Dirac-Brueckner-Hartree-Fock mean field calculations approximated by their parameterized form are the basis of our calculations. We calculated the central pressure and density and correspondingly the possible radius and mass both with and without allowance for hyperons first, and compared these results with recent astronomical observations, and, finally, we included effect of deformation and rotation.
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We used the equations of state of dense nuclear matter to construct the
macroscopic properties of neutron stars and test them using available
observational results. The Dirac-Brueckner-Hartree-Fock mean field
calculations approximated by their parameterized form are the basis of
our calculations. We calculated the central pressure and density and
correspondingly the possible radius and mass both with and without
allowance for hyperons first, and compared these results with recent
astronomical observations, and, finally, we included effect of
deformation and rotation.
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The appearance of corotating Keplerian discs orbiting Kerr superspinars has been shown to be strongly dependent on the value of the superspinar spin in both their shape and frequency shift profile, demonstrating clear distinctions from the corotating discs around black holes. However, it has to be modified in the innermost parts of the disc by the self-illumination effect caused by the photons trapped in the strong gravitational field near the superspinars with spin a < 9. Here we demonstrate that self-illumination is irrelevant for counter-rotating Keplerian discs orbiting in the field of all Kerr superspinars since such discs are located at the regions where none of the radiated photons can be trapped. Therefore, the results obtained by considering the escaping photons only are quite relevant for the appearance of the counter-rotating Keplerian discs orbiting Kerr superspinars. The appearance and spectral continuum of such discs differ from those of counter-rotating discs in the field of Kerr black holes. The differences are of quantitative character except the existence of the disc images located inside the image of the inner edge of the disc that are created by photons reaching regions close to the surface of Kerr superspinars. Their observational relevance is realistic in the near future for accretion phenomena in the vicinity of Sgr A*.
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We summarize influence of the tidal charge parameter of the braneworld models onto some optical phenomena in rotating black hole spacetimes. The shape of an equatorial thin accretion disk and profiled spectral lines of thin keplerian rings around the black holes are given and classified in terms of the black hole rotational and tidal parameters. It is shown that rising of negatively-valued tidal parameter, with rotational parameter fixed, generally strengthens the relativistic effects and suppresses the rotation induced asymmetries in the optical phenomena.
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Humpy profile of the LNRF-related orbital velocity was found for accretion discs orbiting rapidly rotating Kerr black holes with a spin a > 0.9953 (Keplerian discs) and a > 0.99979 (marginally stable thick discs). Maximal positive rate of change of the orbital velocity in terms of the proper radial distance is used to define a local frequency characterising possible physical processes in the disc connected with the velocity hump. Comparing the "humpy frequency" related to distant observers with epicyclic frequencies of perturbed orbital motion, it was shown that in Keplerian discs orbiting near-extreme Kerr black holes (a > 0.998) the the ratio of radial epicyclic frequency and humpy frequency (both evaluated at the same radius) is in terms of small integers asymptotically going to the ratio 3:2 for a → 1. The Extended Orbital Resonance Model with non-linear hump-induced oscillations was applied to two X-ray variable sources GRS 1915+105 and XTE J1650-500. In the case of GRS 1915+105, the model is able to address the whole set of reported QPOs, giving the mass and spin of the central black hole: a = 0.9998; M = 14:8M⊙. For XTE J1650-500, similar ideas give values a = 0.9982; M = 5:1M⊙.
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Using known frequencies of the twin peak quasiperiodic oscillations (QPOs) and the known mass of the central black hole, the black hole dimensionless spin a can be determined, assuming a concrete version of the orbital resonance model. However, because of large range of observationally limited values of the black hole mass, its spin can be estimated with a low precision only. Higher precision of the black hole dimensionless spin measurement is possible in the framework of multi-resonance model of QPOs inspired by complex high-frequency QPO patterns observed in some black hole and neutron star systems.
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We investigate the role of the tidal charge in orbital models of high-frequency quasiperiodic oscillations (QPOs) observed in neutron star binary systems. We show how the standard relativistic precession (RP) model modified by the tidal charge fits the observational data, giving estimates of the allowed values of the tidal charge and the brane tension based on the processes going in the vicinity of neutron stars. We compare our strong field regime restrictions with those given in the weak field limit of solar system experiments.
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We present estimates on the efficiency of neutrino trapping in brany extremely compact stars, using the simplest model with uniform distribution of energy density, assuming massless neutrinos and uniform distribution of neutrino emissivity. Computation have been done for two different uniform-density stellar solution in the Randall-Sundrum II type braneworld, namely with the Reissner-Nordström-type of geometry and the second one, derived by Germani and Maartens.1 Read More
We present equation of state of dense nuclear matter based on relativistic Brueckner—Hartree—Fock theory. The models of static neutron stars are calculated. The results are compared with neutron star models based on Skyrme equations of state and with models of strange stars following MIT bag model.
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Rotating black holes in the brany universe of the Randall—Sundrum type with infinite additional dimension are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b < 0 rotating black holes with dimensionless spin a > 1 are allowed. We investigate the role of the tidal charge in the orbital resonance model of quasiperiodic oscillations (QPOs) in black hole systems.
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