All articles - Astronomy and Astrophysics

Object of the research: black holes, wormholes, gravastars, neutron stars.
Aim of the research: study of electromagnetic fields and particle motion in i) the Kerr-Taub-NUT spacetime, spacetime of ii) rotating magnetized wormhole, iii) black hole on brane, iv) gravastars; derivation of the exact analytic solutions for dependence of radii of stable circular orbits from brane parameter of black holes on brane; study the influence of spin and gravitomagnetic monopole momentum of the black hole on processes of energy extraction from rotating black hole.
Methods of the research: mathematical methods of macroscopic electrodynamics in general relativity, differential geometry, numerical methods of calculation on computers, with further developing of the numerical methods for considered problems.
The obtained results and their novelty: the solutions for electromagnetic fields i) in the Kerr-Taub-NUT spacetime, spacetime of ii) magnetized neutron star with NUT charge, iii) magnetized wormhole, iv) gravastar, v) compact gravitating objects on brane have been found. It has been shown that influence of magnetic field dominates with compare to the NUT charge on charged particle motion in the Kerr-Taub-NUT spacetime and NUT parameter increases the efficiency of Blandfod-Znajek and Penrose processes. Strong dependence of particle motion from form parameter of wormhole has been observed. Exact solution for miminum value of the radii of stable circular orbits around black hole on brane and upper limit for brane parameter have been evaluated. It has been shown that plasma magnetosphere of rotating black hole is stable.
Practical significance: Obtained results can play significant role on detection and study of NUT, brane and other parameters of compact objects. Obtained data can be compared with observed data in order to find the existence and difference wormholes from black holes. Expression for magnetic field of gravastar can be used to describe electromagnetic processes in gravastar. Results allow to get upper limit on value of brane parameter from astrophysical observations on accretion disc around rotating black holes.
Degree of embed and economic effectivity: The dissertation is of theoretical character. The results obtained could be used for studying compact objects in relativistic astrophysics. These scientific results are introduced in the special course «Theory of Gravitation» delivered to graduate students at the National University of Uzbekistan.
Sphere of usage: Relativistic astrophysics, black hole physics, astrophysics of compact objects.

Topicality and demand of the theme of dissertation. Modem astronomical observations on myrovom level on the ground and space telescopes, and recent discoveries have provided convincing evidence that black holes have a significant impact on nearby objects around, emitting powerful gamma-ray bursts, absorbing the next star, and stimulating the growth of newborn stars in the surrounding areas. Study the photons motion around rotating black holes, in particular, the discovery and analysis of the form of silhouettes of these objects, setting and effective implementation of relevant radiostronomical observations on the proof of the existence of the black hole horizon and retrieval of information events on the central object in our galaxy within the Black Hole Cam (BHC) and Event Horizon Telesop (EHT) international projects is one of the most important tasks of modem astrophysics.
In the years of Independence, huge attention is paid to the development of theoretical physics and astronomy and basic research in these areas on a global level. In this regard has been achieved significant results in the field of relativistic astrophysics, in particular, developping a model of the magnetosphere of a neutron star, the analysis of the space-time structure and motion of test particles around black holes.
The study astrophysical processes in the vicinity of compact objects and their comparison with observational data is now one of the most important tasks in astrophysics of compact objects. The most important tasks is to conduct solid research work, in particular studies on following directions: to find the exact solutions describing the space-time around a gravitational compact objects; analysis of space-time structures in the framework of these decisions and find the equation of motion of test particles, such as photons; determining the silhouettes of black holes in general relativity and alternative theories of gravity; determination of the influence of the central object parameters and the plasma environment on the form of a silhouette; identify energy loss dependence on the choice of the relativistic star of the gravity model. These objectives justify the topicality of the global level of scientific research.
This research work corresponds the tasks given by governmental regulatory documents, Orders of President of the Republic of Uzbekistan # UP-559 “Onhigh level astronomical observatories and complexes of their service” from February 11, 1993, # UP-4512 “On works further developing alternative sources of energies” from March 1, 2013.
The aim of the research is the development of a theoretical formalism describing shadows of black holes and the identification of the physical laws of high-cncrgctical processes in the vicinity of rotating black holes.
The scientific novelty of the research is the follows:
For the first time a new coordinate-independent formalism to describe the shape of the black holes shadow has been developed and it was revealed that the first five coefficients of the polynomial expansion is sufficient to describe the properties of rotating black holes shadow with the accuracy of ~0.1%, it has been shown that the proposed definition of distortion of black holes shadow arc stable under the signal noise;
it has been found that the observed size of the shadow of the black hole decreases due to the refraction of electromagnetic radiation in a plasma environment;
for the first time it was shown that for the high efficiency of the ultrahigh-cncrgy processes relative to distant observers, both the non-existence of the horizon, and the strong rotational effects arc necessary;
it was also shown that significant magnification of the efficiency of the ultra-high energy collisions is possible due to additional electromagnetic phenomena influencing collisions of charged particles;
for the first time it was shown that energy extraction through Penrose process is more realistic process among the energy extraction mechanisms from the rotating black hole in Horava-Lifshitz scenario; moreover, due to the Horava-Lifshitz gravity correction particles could be prevented from the infinite acceleration.
for the first time it was shown that the effect of compactness of strange star on the electromagnetic power loss of the star is non-ncgligible;
it was found that the strange star will lose more energy than typical rotating neutron star in general relativity.
CONCLUSION
According to the results of the research carried out on the theme of the doctoral dissertation “Particles and electromagnetic fields around axial-symmetric compact gravitating objects”, the following conclusions arc presented:
1. We have developed a new general and coordinate-independent formalism in which the shadow is described as an arbitrary polar curve expressed in terms of a Legendre expansion. It was revealed that the first five coefficients of the polynomial expansion is sufficient to describe the properties of rotating black holes shadow with the accuracy of -0.1%. Our formalism does not presume any knowledge of the properties of the shadow and offers a number of routes to characterize the properties of the curve. It has been shown that the proposed definition of distortion of black holes shadow arc stable under the signal noise.
2. The analytical expressions for the vacuum electromagnetic fields of deformed rotating black holes in the external asymptotically uniform magnetic field hads been obtained. It has been revealed that the induced electric field around the deformed black hole depends on the deformation parameter linearly, and the magnetic field squared.
3. An upper limit for the deformation parameter for the rotating non-Kerr black hole has been obtained through comparison of the observable values of the radius of innermost stable circular orbits with the theoretical results obtained in the dissertation as £ < 22.
4. It has been obtained the silhouettes of the rotating black holes shadow in the presence of an inhomogeneous plasma, which can be used to identify additional asymmetries in the shape of the shadow and retrieve information on the plasma parameters and the central compact object. 
5. Expressions for energy and momentum, as well as radii of innermost stable circular orbits of charged particles in the vicinity of a black hole with gravitomagnctic charge immersed in external magnetic field has been obtained. It has been established that due to the existence of gravitomagnctic charge particle arc prevented from acceleration to infinitely high cncrgires.
6. It has been shown that In the presence of a plasma the observed shape and size of the shadow changes depending on (i) the plasma parameters, (ii) the black hole spin, and (iii) the inclination angle between the observer plane and the axis of rotation of the black hole. It has been found that the observed size of the shadow of the black hole decreases due to the refraction of electromagnetic radiation in a plasma environment. It was shown that with the increase of the dimensionless plasma parameter, the maximum value of the energy emission rate from the black hole decreases due to the decrease of the size of the black hole shadow.
7. It was shown that for the high efficiency of the ultrahigh-cncrgy processes relative to distant observers, both the non-existence of the horizon, and the strong rotational effects arc necessary; it was also shown that significant magnification of the efficiency of the ultra-high energy collisions is possible due to additional electromagnetic phenomena influencing collisions of charged particles.
8. It was shown that energy extraction through Penrose process is more realistic process among the energy extraction mechanisms from the rotating black hole in Horava-Lifshitz scenario; moreover, due to the Horava-Lifshitz gravity correction particles could be prevented from the infinite acceleration.
9. It was shown that the effect of compactness of strange star on the electromagnetic power loss of the star is non-ncgligiblc and may help in future in distinguishing the strange star model via pulsar timing observations. It was found that the relativistic strange star would lose more energy than typical rotating neutron star in general relativity. The obtained dependence may be useful in further investigations of the possible dctcction/distinguishmcnt of the strange stars.