Ahmadjon Abdujabbarov

Test particle motion around a black hole in a braneworld

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) r{sub ISCO} 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 r{sub ISCO} is monotonically growing with the increase of the module of the brane tidal charge. A comparison of the predictions on r{sub ISCO} 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 < or approx. 10{sup 9} cm{sup 2}.

Shadow of Kerr-Taub-NUT black hole

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.

Particle Motion around Black Hole in Horava-Lifshitz Gravity

Analytical solutions of Maxwell equations around a black hole immersed in an external uniform magnetic field in the background of the Kehagias-Sfetsos (KS) asymptotically flat black hole solution of Horava-Lifshitz gravity have been found. The influence of a magnetic field on the effective potential of the radial motion of a charged test particle around a black hole immersed in an external magnetic field in Horava-Lifshitz gravity has been investigated by using the Hamilton-Jacobi method. An exact analytical solution for dependence of the minimal radius of the circular orbits r{sub mc} from KS parameter {omega} for motion of a test particle around a spherical symmetric black hole in Horava-Lifshitz gravity has been derived. The critical values of the particles angular momentum for captured particles by a black hole in Horava-Lifshitz gravity have been obtained numerically. The comparison of the obtained numerical results with the astrophysical observational data on the radii of the innermost stable circular orbits gives us the estimation of the parameter as {omega}{approx_equal}3.6{center_dot}10{sup -24} cm{sup -2}.

Acceleration of particles by black hole with gravitomagnetic charge immersed in magnetic field

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.

Energy Extraction and Particle Acceleration Around Rotating Black Hole in Horava-Lifshitz Gravity

The Penrose process on rotational energy extraction of the black hole in the original nonprojectable Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity is studied. The strong dependence of the extracted energy from the special range of parameters of the Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity, such as parameter

Shadow of the rotating black hole with quintessential energy in the presence of plasma

{\ensuremath{\Lambda}}_{W}

Particle acceleration around a five-dimensional Kerr black hole

and specific angular momentum

Magnetized particle motion and acceleration around a Schwarzschild black hole in a magnetic field

a

Magnetized particle capture cross section for braneworld black hole

, has been found. Particle acceleration near the rotating black hole in Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity has been studied. It is shown that the fundamental parameter of the Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity can impose a limitation on the energy of the accelerating particles preventing them from the infinite value.

Gravitational lensing by regular black holes surrounded by plasma

We study the shadow of the rotating black hole with quintessential energy (i) in vacuum, (ii) in the presence of plasma with radial power-law density. For the vacuum case, the quintessential field parameter of the rotating black hole significantly changes the shape of the shadow. With increasing quintessential field parameter, the radius of the shadow also increases. With the increase of the radius of the shadow of the rotating black hole, the quintessential field parameter causes decrease of the distortion of the shadow shape: in the presence of the quintessential field parameter, the shadow of the fast rotating black hole becomes too close to the circle. We assume the distant observer of the black hole shadow to be located near the so-called static radius where the gravitational attraction of the black hole is just balanced by the cosmic repulsion. The shape and size of the shadow of quintessential rotating black hole surrounded by plasma depends on (i) plasma parameters, (ii) black hole spin and (iii) quintessential field parameter. With the increase of the plasma refraction index, the apparent radius of the shadow increases. However, for the large values of the quintessential field parameter, the change of the black hole shadow shape due to the presence of plasma is not significant, i.e. the effect of the quintessential field parameter dominates over the plasma effect.