Mühendislik Fakültesi / Faculty of Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11727/1401

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Author: search.filters.author.Azreg-Ainou, Mustapha

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    Hamiltonian Formulation Of Relativistic Magnetohydrodynamic Accretion On A General Spherically Symmetric And Static Black Hole: Quantum Effects On Shock States
    (EUROPEAN PHYSICAL JOURNAL C, 2024-11-19) Azreg-Ainou, Mustapha; Jamil, Mubasher; Noda, Sousuke
    In this paper, our aim is to extend our earlier work [Ahmed et al. in Eur. Phys. J. C 76:280, 2016], investigating an axisymmetric plasma flow with angular momentum onto a spherical black hole. To accomplish that goal, we focus on the case in which the ideal magnetohydrodynamic approximation is valid, utilizing certain conservation laws which arise from particular symmetries of the system. After formulating a Hamiltonian of the physical system, we solve the Hamilton equations and look for critical solutions of (both in and out) flows. Reflecting the difference from the Schwarzschild spacetime, the positions of sonic points (fast magnetosonic point, slow magnetosonic point, Alfv & eacute;n point) are altered. We explore several kinds of flows including critical, non-critical, global, magnetically arrested and shock induced. Lastly, we analyze the shock states near a specific quantum corrected Schwarzschild black hole and determine that quantum effects do not favor shock states by pushing the shock location outward.
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    Traversable Morris-Thorne-Buchdahl Wormholes in Quadratic Gravity
    (2023) Nguyen, Hoang Ky; Azreg-Ainou, Mustapha; 0000-0002-3244-7195
    The special Buchdahl-inspiredmetric obtained in a recent paper [Phys. Rev. D 107, 104008 (2023)] describes asymptotically flat spacetimes in pure R-2 gravity. The metric depends on a new (Buchdahl) parameter (k) over tilde of higher-derivative characteristic, and recovers the Schwarzschild metric when (k) over tilde = 0. It is shown that the special Buchdahlinspired metric supports a two-way traversable MorrisThorne wormhole for (k) over tilde is an element of (-1, 0) in which case the Weak Energy Condition is formally violated, a naked singularity for (k) over tilde is an element of (-infinity,-1). (0,+infinity), and a non-Schwarzschild structure for (k) over tilde = -1.
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    Constraining Wormhole Geometries Using The Orbit Of S2 Star And The Event Horizon Telescope
    (2022) Jusufi, Kimet; Kumar, Saurabh; Azreg-Ainou, Mustapha; Jamil, Mubasher; Wu, Qiang; Bambi, Cosimo
    In this paper we study the possibility of having a wormhole (WH) as a candidate for the Sgr A(star) central object and test this idea by constraining their geometry using the motion of S2 star and the reconstructed shadow images. In particular, we consider three WH models, including WHs in Einstein theory, brane-world gravity, and Einstein-Dirac-Maxwell theory. To this end, we have constrained the WH throat using the motion of S2 star and shown that the flare out condition is satisfied. We also consider the accretion of infalling gas model and study the accretion rate and the intensity of the electromagnetic radiation as well as the shadow images.
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    Constraining the generalized uncertainty principle through black hole shadow, S2 star orbit, and quasiperiodic oscillations
    (2022) Jusufi, Kimet; Azreg-Ainou, Mustapha; Jamil, Mubasher; Zhu, Tao
    In this paper, we study the effect of the Generalized Uncertainty Principle (GUP) on the shadow of GUP-modified Kerr black hole and the correspondence between the shadow radius and the real part of the quasinormal modes (QNMs). We find that the shadow curvature radius of the GUP-modified Kerr black hole is bigger compared to the Kerr vacuum solution and increases linearly monotonically with the increase of the GUP parameter. We then investigate the characteristic points of intrinsic curvature of the shadow from a topological point of view to calculate the angular size for these curvature radii of the shadow. To this end, we have used the EHT data for the M87* black hole to constrain the upper limits of the GUP parameter and our result is beta < 10(95). Finally, we have explored the connection between the shadow radius and the scalar/electromagnetic/gravitational QNMs. Using the orbit of S2 star we have obtained a bound for the GUP parameter beta < 10(87). The GUP-modified Kerr black hole is also used to provide perfect curve fitting of the particle oscillation upper and lower frequencies to the observed frequencies for three microquasars and to restrict the values of the correction parameter in the metric of the modified black hole to very reasonable bound beta < 10(77).
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    Constraints on Barrow Entropy from M87* and S2 Star Observations
    (2022) Jusufi, Kimet; Azreg-Ainou, Mustapha; Jamil, Mubasher; Saridakis, Emmanuel N.
    We use data from M87* central black hole shadow, as well as from the S2 star observations, in order to extract constraints on Barrow entropy. The latter is a modified entropy arising from quantum-gravitational effects on the black hole horizon, quantified by the new parameter & UDelta;. Such a change in entropy leads to a change in temperature, as well as to the properties of the black hole and its shadow. We investigate the photon sphere and the shadow of a black hole with Barrow entropy, and assuming a simple model for infalling and radiating gas we estimate the corresponding intensity. Furthermore, we use the radius in order to extract the real part of the quasinormal modes, and for completeness we investigate the spherical accretion of matter onto the black hole, focusing on isothermal and polytropic test fluids. We extract the allowed parameter region, and by applying a Monte-Carlo-Markov Chains analysis we find that & UDelta;& SIME; 0.0036(-0.0145)(+0.0792). Hence, our results place the upper bound & UDelta;& LSIM;0.0828 at 1 sigma, a constraint that is less strong than the Big Bang Nucleosynthesis one, but significantly stronger than the late-time cosmological constraints.
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    Quasinormal modes, quasiperiodic oscillations, and the shadow of rotating regular black holes in nonminimally coupled Einstein-Yang-Mills theory
    (2021) Jusufi, Kimet; Azreg-Ainou, Mustapha; Jamil, Mubasher; Wei, Shao-Wen; Wu, Qiang; Wang, Anzhong; AAZ-1598-2021
    In this paper, we obtain an effective metric describing a regular and rotating magnetic black hole (BH) solution with a Yang-Mills electromagnetic source in Einstein-Yang-Mills (EYM) theory using the Newman-Janis (NJ) algorithm via the noncomplexification radial coordinate procedure. We then study the BH shadow and the quasinormal modes (QNMs) for massless scalar and electromagnetic fields and the quasiperiodic oscillations (QPOs). To this end, we also study the embedding diagram for the rotating EYM BH. The energy conditions, shadow curvature radius, topology, and the dynamical evolution of scalar and electromagnetic perturbations using the time domain integration method are investigated. We show that the shadow radius decreases by increasing the magnetic charge, while the real part of QNMs of scalar and electromagnetic fields increases by increasing the magnetic charge. This result is consistent with the inverse relation between the shadow radius and the real part of QNMs. In addition, we have studied observational constraints on the EYM parameter. via frequency analysis of QPOs and the EHT data of shadow cast by the M87 central black hole. We also find that the decaying rate of the EYM BH is slower than that of the neutral and ends up with a tail. We argue that the rotating EYM black hole can be distinguished from the Kerr-Newman black hole with a magnetic charge based on the difference between the angular diameters of their shadows.
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    Rotating Cosmological Cylindrical Wormholes in GR and TEGR Sourced by Anisotropic Fluids
    (2021) Azreg-Ainou, Mustapha; AAZ-1598-2021
    Given an anisotropic fluid source, we determine in closed forms, upon solving the field equations of general relativity (GR) and teleparallel gravity (TEGR) coupled to a cosmological constant, cylindrically symmetric four-dimensional cosmological rotating wormholes, satisfying all local energy conditions, and cosmological rotating solutions with two axes of symmetry at finite proper distance. These solutions have the property that their angular velocity is proportional to the cosmological constant. (C) 2021 Elsevier B.V. All rights reserved.
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    Axion-plasmon or magnetized plasma effect on an observable shadow and gravitational lensing of a Schwarzschild black hole
    (2021) Atamurotov, Farruh; Jusufi, Kimet; Jamil, Mubasher; Abdujabbarov, Ahmadjon; Azreg-Ainou, Mustapha; AAZ-1598-2021
    In this paper, we study the influence of the axion-plasmon, as proposed in [Phys. Rev. Lett. 120, 181803 (2018)] on the optical properties of the Schwarzschild black hole. Our aim is to provide a test to detect the effects of a fixed axion background using black holes. To accomplish our goal, we explore the effect of the axion-plasmon coupling on the motion of photons around the Schwarzschild black hole and check the possibility of observing those effects upon the black hole shadow, the gravitational deflection angle, Einstein rings and shadow images obtained by radially infalling gas on a black hole within a plasma medium. We find that these quantities are indeed affected by the axion-plasmon coupling parameters which consequently generalize some of the well-known results in the literature. It is shown that the size of the black hole shadow decreases with increasing axion-plasmon if observed from a sufficiently large distance.
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    Shadow and quasinormal modes of a rotating loop quantum black hole
    (2020) Liu, Cheng; Zhu, Tao; Wu, Qiang; Jusufi, Kimet; Jamil, Mubasher; Azreg-Ainou, Mustapha; Wang, Anzhong
    In this paper, we construct an effective rotating loop quantum black hole (LQBH) solution, starting from the spherical symmetric LQBH by applying the Newman-Janis algorithm modified by Azreg-Ainou's noncomplexification procedure, and study the effects of loop quantum gravity (LQG) on its shadow. Given the rotating LQBH, we discuss its horizon, ergosurface, and regularity as r -> 0. Depending on the values of the specific angular momentum a and the polymeric function P arising from LQG, we find that the rotating solution we obtained can represent a regular black hole, a regular extreme black hole, or a regular spacetime without horizon (a non-black-hole solution). We also study the effects of LQG and rotation, and show that, in addition to the specific angular momentum, the polymeric function also causes deformations in the size and shape of the black hole shadow. Interestingly, for a given value of a and inclination angle theta(0), the apparent size of the shadow monotonically decreases, and the shadow gets more distorted with increasing P. We also consider the effects of P on the deviations from the circularity of the shadow, and find that the deviation from circularity increases with increasing P for fixed values of a and theta(0). Additionally, we explore the observational implications of P in comparing with the latest Event Horizon Telescope observation of the supermassive black hole, M87*. The connection between the shadow radius and quasinomial modes in the eikonal limit as well as the deflection of massive particles are also considered.
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    Cylindrically symmetric static n-dimensional (un)charged (anti-)de Sitter black holes in generic f(T) gravity
    (2020) Azreg-Ainou, Mustapha
    Given a generic function f(T) we construct in closed forms cylindrically symmetric static n-dimensional uncharged and charged de Sitter and anti-de Sitter solutions (including black holes, wormholes and possibly other regular solutions) in f(T) gravity. Applications to some known models are considered. Copyright (C) EPLA, 2020