Bobomurat Ahmedov

Institute of Nuclear Physics, Toshkent, Toshkent Shahri, Uzbekistan

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Publications (12)20.27 Total impact

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    ABSTRACT: The particle acceleration mechanism in $S^2 \times\mathbb{R}^1$ topology, namely in the spacetime of the five-dimensional compact black string has been studied. The expression of center-of-mass energy of the colliding neutral particles near static black string has been found. The collision of charged particle moving at the innermost stable circular orbit with neutral particle coming from infinity have been considered when black string is immersed in external uniform magnetic field. It has been shown that the unlimited center-of-mass energy can be approached in case of the extremal rotation of the black string which is similar to the analogous effect in the Kerr spacetime. We have also obtained that the scattering energy of particles in the center-of-mass system can take arbitrary large values not only for extremal black string but also for nonextremal one. It has been derived that the presence of the extra dimension can, in principle, increase the upper limit of efficiency of energy extraction from the extremely rotating black string up to $203\%$ versus to $143\%$ which can be extracted from the extreme Kerr black hole.
    Physical Review D 11/2013; · 4.69 Impact Factor
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    ABSTRACT: The shadow of rotating Hořava-Lifshitz black hole has been studied and it was shown that in addition to the specific angular momentum a, parameters of Hořava-Lifshitz spacetime essentially deform the shape of the black hole shadow. For a given value of the black hole spin parameter a, the presence of a parameter Λ W and KS parameter ω enlarges the shadow and reduces its deformation with respect to the one in the Kerr spacetime. We have found a dependence of radius of the shadow R s and distortion parameter δ s from parameter Λ W and KS parameter ω both. Optical features of the rotating Hořava-Lifshitz black hole solutions are treated as emphasizing the rotation of the polarization vector along null congruences. A comparison of the obtained theoretical results on polarization angle with the observational data on Faraday rotation measurements provides the upper limit for the δ parameter as δ≤2.1⋅10−3.
    Astrophysics and Space Science 11/2013; · 2.06 Impact Factor
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    ABSTRACT: On the lines of the 4-dimensional Kerr black hole we consider the particle acceleration near a 5-dimensional Kerr black hole which has the two rotation parameters. It turns out that the center of mass energy of the two equal mass colliding particles as expected diverges for the extremal black hole and there is a symmetry in the results for $\theta = 0, \pi/2$. Because of the two rotation parameters, $r=0$ can be a horizon without being a curvature singularity. It is shown that the acceleration of particles to high energies near the 5-D extreme rotating black hole avoids fine-tuning of the angular momentum of particles.
    Physical Review D 10/2013; 88(8). · 4.69 Impact Factor
  • Farruh Atamurotov, Bobomurat Ahmedov, Sanjar Shaymatov
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    ABSTRACT: We study mechanism of formation of black holes (BHs) from collisions of particles in the vicinity of the supermassive black hole acting as a particle accelerator trough BSW (Banados-Silk-West) effect. Moreover, we also investigate BH-BH collision, in which stellar black holes colliding near the horizon of a rotating supermassive black hole can reach large values of the center-of-mass energy. This result implies that high arbitrary energy of collisions causes to be transformed into radiation energy and particles, which might bring possible visible signals through the astrophysical observations. We study the radiation energy from a collision of two accelerating stellar black holes and find a maximal value of the radiation energy to be nearly E rad ≈2.5⋅1056 erg for the ultrarelativistic value of v/c=0.99 from BH-BH collisions.
    Astrophysics and Space Science 10/2013; · 2.06 Impact Factor
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    ABSTRACT: The shadow of a rotating non-Kerr black hole has been studied, and it was shown that in addition to the specific angular momentum a, the deformation parameter of non-Kerr spacetime essentially deforms the shape of the black hole shadow. For a given value of the black hole spin parameter a, the presence of a deformation parameter ϵ reduces the shadow and enlarges its deformation with respect to the one in the Kerr spacetime. Optical features of the rotating non-Kerr black hole in terms of rotation of the polarization vector along null congruences have been studied. A comparison of the obtained theoretical results on the polarization angle with the observational data on Faraday rotation measurements provides the upper limit for the dimensionless deformation parameter as ϵ≤19.
    Physical Review D 09/2013; 88(6). · 4.69 Impact Factor
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    ABSTRACT: The stellar magnetic field configuration and solutions of Maxwell equations in the external background spacetime of a magnetized spherical stars in the Hořava-Lifshitz gravity and in modified f(R) gravity are studied. The star is modeled as a sphere consisting of perfect highly magnetized fluid with infinite conductivity and frozen-in magnetic field. With respect to solutions for magnetic fields found in the Schwarzschild spacetime star in modified gravity theories, enhancing corrections are added to the exterior magnetic field. The energy losses through magnetodipolar radiation of the rotating magnetized compact star within alternative gravity theories is also considered. The question of whether these models can be considered as an alternative theory for general relativity is also discussed through astrophysical application of the obtained magnetodipolar energy loss formula. Finally we analyze the role of general relativistic effect on the decay of a neutron star’s magnetic field in modified theories of gravity.
    Physical review D: Particles and fields 07/2013; 88(2).
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    ABSTRACT: We study motion of an electric current-carrying string loop oscillating in the vicinity of the Schwarzschild black hole immersed in an external uniform magnetic field. The dependence of boundaries and different types of motion of the string loop on magnetic field strength is found. The dynamics of the string loop in the Cartesian xy plane depends both on value and direction of the magnetic field and current. It is shown that the magnetic field influence on the behavior of the string loop is quite significant even for weak magnetic field strength. The oscillation of the string loop becomes stronger or weaker in dependence on the direction of the Lorenz force. We illustrate the various regimes of the trajectories of the string loop that can fall down into the black hole, escape to infinity, or be trapped in the finite region near the horizon for the different representative values of the magnetic field. We have also considered the flat spacetime limit as the condition of the escape of the string loop from the neighborhood of the black hole to infinity. We found the expression for the magnetic field strength for which the oscillatory motion of the string loop totally vanishes and the string loop can have maximal acceleration in the perpendicular direction to the plane of the loop.
    Physical review D: Particles and fields 06/2013; 87(12).
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    ABSTRACT: We present analytical solutions of Maxwell’s equations around a rotating non-Kerr black hole immersed in an external uniform magnetic field. The influence of a magnetic field on the effective potential of the radial motion of a charged test particle around a rotating non-Kerr black hole immersed in an external magnetic field are investigated by using the Hamilton-Jacobi equation of motion. The dependence of the minimal radius of the circular orbits rmc and the radius of the innermost stable circular orbits (ISCOs) from the deformation and the magnetic parameters for the motion of charged particles around a rotating non-Kerr black hole are also presented. An increase of the magnetic field decreases the ISCO radius, while the negative deformation parameter may lead to a larger ISCO radius. A comparison of the numerical results of ISCOs around a non-Kerr black hole with the observational data for the ISCO radius of rapidly rotating black holes [R. Shafee et al., Astrophys. J. 636 L113 (2006)] provides the upper limit for the deformation parameter as ϵ≤22.
    Physical review D: Particles and fields 03/2013; 87(6).
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    ABSTRACT: The shadow of a rotating black hole with nonvanishing gravitomagnetic charge has been studied. It was shown that in addition to the angular momentum of black hole the gravitomagnetic charge term deforms the shape of the black hole shadow. From the numerical results we have obtained that for a given value of the rotation parameter, the presence of a gravitomagnetic charge enlarges the shadow and reduces its deformation with respect to the spacetime without gravitomagnetic charge. Finally we have studied the capture cross section for massive particles by black hole with the nonvanishing gravitomagnetic charge.
    Astrophysics and Space Science 12/2012; 344(2). · 2.06 Impact Factor
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    ABSTRACT: Penrose process on rotational energy extraction of the black hole (BH) in the original non-projectable Ho\v{r}ava-Lifshitz gravity is studied. The strong dependence of the extracted energy from the special range of parameters of the Ho\v{r}ava-Lifshitz gravity, such as parameter $\Lambda_W$ and specific angular momentum $a$ has been found. Particle acceleration near the rotating BH in Ho\v{r}ava-Lifshitz gravity has been studied. It is shown that the fundamental parameter of the Ho\v{r}ava-Lifshitz gravity can impose limitation on the the energy of the accelerating particles preventing them from the infinite value.
    Physical review D: Particles and fields 07/2011; 84(4).
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    ABSTRACT: Analytical solutions of Maxwell equations around black hole immersed in external uniform mag-netic field in the background of the Kehagias-Sfetsos (KS) asymptotically flat black hole solution of Hořava-Lifshitz gravity have been found. Influence of magnetic field on effective potential of the radial motion of charged test particle around black hole immersed in external magnetic field in Hořava-Lifshitz gravity has been investigated by using Hamilton-Jacobi method. Exact analytical solution for dependence of the minimal radius of the circular orbits rmc from KS parameter ω for motion of test particle around spherical symmetric black hole in Hořava-Lifshitz gravity has been derived. The critical values of the particle's angular momentum for captured particles by black hole in Hořava-Lifshitz gravity have been obtained numerically. The comparison of the obtained numerical results with the astrophysical observational data on radii of the innermost stable circular orbits gives us the estimation of the parameter as ω ≃ 3.6 · 10 −24 cm −2 .
    Physical review D: Particles and fields 02/2011; 83(4).
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    Ahmadjon Abdujabbarov, Bobomurat Ahmedov
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    ABSTRACT: Analytical solutions of Maxwell equations in background spacetime of a black hole in a braneworld immersed in an external uniform magnetic field have been found. The influence of both magnetic and brane parameters on the effective potential of the radial motion of a charged test particle around a slowly rotating black hole in a braneworld immersed in a uniform magnetic field has been investigated by using the Hamilton-Jacobi method. An exact analytical solution for dependence of the radius of the innermost stable circular orbits (ISCO) rISCO from the brane parameter for the motion of a test particle around a nonrotating isolated black hole in a braneworld has been derived. It has been shown that the radius rISCO is monotonically growing with the increase of the module of the brane tidal charge. A comparison of the predictions on rISCO of the braneworld model and of the observational results of ISCO from relativistic accretion disks around black holes provided the upper limit for the brane tidal charge ≲109 cm2.
    Physical review D: Particles and fields 05/2009; 81(4).