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, MustaphaSubject: search.filters.subject.GEODESIC MOTION

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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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    Orbital mechanics and quasiperiodic oscillation resonances of black holes in Einstein-AEther theory
    (2020) Azreg-Ainou, Mustapha; Chen, Zihang; Deng, Bojun; Jamil, Mubasher; Zhu, Tao; Wu, Qiang; Lim, Yen-Kheng
    In this paper, we study the motion of test particles around two exact charged black hole solutions in Einstein-AEther theory. Specifically, we first consider the quasiperiodic oscillations (QPOs) and their resonances generated by the particle moving in the Einstein-AEther black hole and then turn to study the periodic orbits of the massive particles. For QPOs, we drop the usually adopted assumptions nu(U) = nu(theta), nu(L) = nu(r), and nu(U)/nu(L) = 3/2 with nu(U) (nu(L)) and nu(r) (nu(theta)) being the upper (lower) frequency of QPOs and radial (vertical) epicyclic frequency of the orbiting particles, respectively. Instead, we put-forward a new working ansatz for which the Keplerian radius is much closer to that of the innermost stable circular orbit and explore in detail the effects of the aether field on the frequencies of QPOs. We then realize good curves for the frequencies of QPOs, which fit to data of three microquasars very well by ignoring any effects of rotation and magnetic fields. The innermost stable circular orbits (isco) of timelike particles are also analyzed, and we find the isco radius increases with increasing c(13) for the first type black hole while decreases with increasing c(14) for the second one. We also obtain several periodic orbits and find that they share similar taxonomy schemes as the periodic equatorial orbits in the Schwarzschild/Kerr metrics, in addition to exact solutions for certain choices of the Einstein-AE ther parameters. The equations for null geodesics are also briefly considered, where we study circular photon orbits and bending angles for gravitational lensing.
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    Shadow, quasinormal modes, and quasiperiodic oscillations of rotating Kaluza-Klein black holes
    (2020) Ghasemi-Nodehi, M.; Azreg-Ainou, Mustapha; Jusufi, Kimet; Jamil, Mubasher
    In this paper we study the shadow of rotating Kaluza-Klein (KK) black holes and the connection between the shadow radius and the real part of quasinormal modes (QNMs) in the eiokonal limit. In addition we have explored the quasiperiodic oscillations (QPOs) in the rotating KK black hole.