Ulugh Begh Astronomical Institute

Tashkent, Uzbekistan

Ulugh Begh Astronomical Institute

Tashkent, Uzbekistan
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Morozova V.S.,Max Planck Institute For Gravitationsphysik | Morozova V.S.,Institute of Nuclear Physics of Uzbekistan | Ahmedov B.J.,Institute of Nuclear Physics of Uzbekistan | Ahmedov B.J.,Ulugh Begh Astronomical Institute | And 3 more authors.
Astrophysics and Space Science | Year: 2013

We study gravitational lensing in the vicinity of a slowly rotating massive object surrounded by a plasma. We have studied two effects: (i) the influence of the frame dragging on the deflection angle of the light ray in the presence of plasma (ii) Faraday rotation of the polarization plane of the light. We derive the expression for the lensing angle in a non-diagonal space-time in the weak field regime in the presence of plasma and discuss it for the spacetime metric of the slowly rotating object. The obtained deflection angle depends on (i) the frequency of the electromagnetic wave, due to the dispersion properties of the plasma; (ii) the gravitational mass M; and (iii) the angular momentum J of the gravitational lens. We studied the influence of rotation of the gravitational lens on the magnification of brightness of the source star in the case of microlensing and have shown that it is negligibly small. For the completeness of our study the effect of the Faraday rotation of the polarization plane is considered. © 2013 Springer Science+Business Media Dordrecht.


Atamurotov F.,Institute of Nuclear Physics of Uzbekistan | Abdujabbarov A.,Institute of Nuclear Physics of Uzbekistan | Abdujabbarov A.,Ulugh Begh Astronomical Institute | Ahmedov B.,Institute of Nuclear Physics of Uzbekistan | And 2 more authors.
Astrophysics and Space Science | Year: 2013

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{dot operator}10-3. © 2013 Springer Science+Business Media Dordrecht.


Tursunov A.,Institute of Nuclear Physics of Uzbekistan | Tursunov A.,Ulugh Begh Astronomical Institute | Tursunov A.,Silesian University in Opava | Kolos M.,Silesian University in Opava | And 5 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The particle acceleration mechanism in S2×R1 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 a charged particle moving at the innermost stable circular orbit with a neutral particle coming from infinity has 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 the case of the extremal rotation of the black string which is similar to the analogous effect in Kerr spacetime. We have also obtained that the scattering energy of particles in the center-of-mass system can take arbitrarily large values not only for extremal black string but also for the 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 143% which can be extracted from the extreme Kerr black hole. © 2013 American Physical Society.


Tursunov A.,Institute of Nuclear Physics of Uzbekistan | Tursunov A.,Ulugh Begh Astronomical Institute | Tursunov A.,Max Planck Institute For Gravitationsphysik | Kolos M.,Silesian University in Opava | And 4 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

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. © 2013 American Physical Society.


Tursunov A.,Silesian University in Opava | Tursunov A.,Institute of Nuclear Physics of Uzbekistan | Kolos M.,Silesian University in Opava | Stuchlik Z.,Silesian University in Opava | And 2 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study the acceleration of an electric current-carrying and axially symmetric string loop initially oscillating in the vicinity of a Schwarzschild black hole embedded in an external asymptotically uniform magnetic field. The plane of the string loop is orthogonal to the magnetic field lines and the acceleration of the string loop occurs due to the transmutation effect turning in the deep gravitational field the internal energy of the oscillating strings to the energy of their translational motion along the axis given by the symmetry of the black hole spacetime and the magnetic field. We restrict our attention to the motion of string loop with energy high enough, when it can overcome the gravitational attraction and escape to infinity. We demonstrate that for the current-carrying string loop the transmutation effect is enhanced by the contribution of the interaction between the electric current of the string loop and the external magnetic field and we give conditions that have to be fulfilled for an efficient acceleration. The Schwarzschild black hole combined with the strong external magnetic field can accelerate the current-carrying string loop up to the velocities close to the speed of light v∼c. Therefore, the string loop transmutation effect can potentially well serve as an explanation for acceleration of highly relativistic jets observed in microquasars and active galactic nuclei. © 2014 American Physical Society.


Rahimov O.G.,Institute of Nuclear Physics of Uzbekistan | Rahimov O.G.,Ulugh Begh Astronomical Institute
Modern Physics Letters A | Year: 2011

We investigate the motion of a magnetized particle orbiting around a black hole in braneworld immersed in asymptotically uniform magnetic field. The influence of brane parameter on effective potential of the radial motion of magnetized spinning particle around the braneworld black hole using Hamilton-Jacobi formalism is studied. It is found that circular orbits for photons and slowly moving particles may become stable near r = 3M. It was argued that the radii of the innermost stable circular orbits are sensitive on the change of brane parameter. Similar discussion without Weil parameter has been considered by de Felice et al. in Refs. 1 and 2. © 2011 World Scientific Publishing Company.


Hakimov A.,Ulugh Begh Astronomical Institute | Atamurotov F.,Institute of Nuclear Physics of Uzbekistan | Atamurotov F.,Inha University
Astrophysics and Space Science | Year: 2016

We study gravitational lensing in the vicinity of a massive object described by non-Schwarzschild geometry surrounded by a homogeneous plasma. The expression for the deflection angle in a non-Schwarzschild space-time in the weak field regime in the presence of plasma have been derived. It has been shown that the obtained deflection angle depends on (i) the frequency of the electromagnetic wave, due to the dispersion properties of the plasma; (ii) the gravitational mass  (Formula presented.) ; and (iii) deformation parameter (Formula presented.) of the gravitational lens. Moreover, the influence of deformation parameter of the gravitational lens and plasma frequency on the magnification of brightness of the source star has been studied in the case of microlensing. © 2016, Springer Science+Business Media Dordrecht.


Abdujabbarov A.A.,Institute of Nuclear Physics of Uzbekistan | Abdujabbarov A.A.,Ulugh Begh Astronomical Institute | Tursunov A.A.,Institute of Nuclear Physics of Uzbekistan | Tursunov A.A.,Ulugh Begh Astronomical Institute | And 4 more authors.
Astrophysics and Space Science | Year: 2013

The collision of test charged particles in the vicinity of an event horizon of a weakly magnetized non-rotating black hole with gravitomagnetic charge has been studied. The presence of the external magnetic field decreases the innermost stable circular orbits (ISCO) radii of charged particles. The opposite mechanism occurs when there is nonvanishing gravitomagnetic charge. For a collision of charged particle moving at ISCO and the neutral particle falling from infinity the maximal collision energy can be decreased by gravitomagnetic charge in the presence of external asymptotically uniform magnetic field. © 2012 Springer Science+Business Media Dordrecht.


Abdujabbarov A.,Institute of Nuclear Physics of Uzbekistan | Abdujabbarov A.,Ulugh Begh Astronomical Institute | Atamurotov F.,Institute of Nuclear Physics of Uzbekistan | Atamurotov F.,National University of Uzbekistan | And 4 more authors.
Astrophysics and Space Science | Year: 2013

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. © 2012 Springer Science+Business Media Dordrecht.


Rayimbaev J.R.,Ulugh Begh Astronomical Institute
Astrophysics and Space Science | Year: 2016

The motion of a magnetized particle orbiting around non-Schwarzschild black hole immersed in an external uniform magnetic field is considered. The influence of deformation parameter h to effective potential of the radial motion of the magnetized particle around non-Schwarzschild black hole using Hamilton-Jacobi formalism is studied. We have obtained numerical values of area Δ ρ where magnetized particles can move which is expanding (narrowing) due to the effect of the negative (positive) deformation. Finally, we have studied the collision of two particles (magnetized-neutral, magnetized-magnetized, magnetized-charged) in non-Schwarzschild spacetime and got the center-of-mass energy (Ec . m) for the particles. Moreover, we have found the capture radius (rc a p) – the distance from the central object to the point where particles collide and fall down to the central compact object. It is shown that non-Schwarzschild black holes could also act as particle accelerators with arbitrarily high center-of-mass energy. © 2016, Springer Science+Business Media Dordrecht.

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