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Properties of multi black-hole spacetimes
Klimešová, Eliška ; Žofka, Martin (advisor) ; Tahamtan, Tayebeh (referee)
In Newtonian physics, a system of extremally charged particles (electric charge equal to gravitational mass in geometrized units) remains in a static equilibrium until an external force is applied. This situation, surprisingly, translates exactly to general relativity in the case of extremely charged black holes, as was inde- pendently shown by Sudhansu Datta Majumdar and Achilles Papapetrou in 1947. Moreover, if the system is perturbed, giving the black holes small initial velocities vi ≪ c, it can be described by a metric first discussed by Robert Craig Ferrell and Douglas Michael Eardley in 1987. We examine whether it is possible to arrive at the perturbed metric in some special cases, such as boosting or spinning up the original static metric. We further study the case of two inter- acting black holes, which is equivalent to a classical mechanics problem with a special Lagrangian. We discuss the critical impact parameter separating cases of coalescing and scattering black holes as they spiral closer together from infinity. We find the critical value as a function of the ratio of the black holes' masses. Finally, we compare the limiting case where one of the holes is much heavier than the other to a trajectory of an extremally charged test particle in extremal Reissner-Nordstr¨om. 1
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Exact solutions with matter fields
Kokoška, David ; Ortaggio, Marcello (advisor) ; Žofka, Martin (referee)
In this thesis we investigate Robinson-Trautman solutions of Einstein's gravity cou- pled to a matter field in higher dimensions, specifically a conformally invariant and non- linear electromagnetic field. The latter possesses in general a non-zero energy-momentum tensor, which provides a source term in Einstein's equations. We focus concretely on an electromagnetic field aligned with the null vector field generating the expanding con- gruence of Robinson-Trautman spacetimes. At the beginning, we review the concept of optical scalars for a null vector field in higher dimensions and we use those to define the higher-dimensional Robinson-Trautman class of spacetimes. Next, we solve the corre- sponding Einstein's equations and present the complete family of exact solutions of the theory under consideration. We then contrast the obtained results with the known ones for the linear Maxwell theory in higher dimensions. As a check, we also compare our results to the well-known results in D = 4, since in this case our matter theory reduces to the standard linear Maxwell theory. Finally, we study properties of a subfamily of solutions which represent the static black holes within our class. In particular, we ana- lyze the asymptotic behaviour, we show that a curvature singularity is always present for r → 0 and the...
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De Sitter special relativity
Vrecion, Jiří ; Svítek, Otakar (advisor) ; Žofka, Martin (referee)
This thesis deals with de Sitter space as an alternative to Minkowski space, which is generally used in theories describing matter and fields (for example quantum field theory). The problem of mass in de Sitter space is analyzed in more detail. The mathematical apparatus needed in this thesis, from factor groups, through Lie groups and algebras to Casimir operators, is also mentioned. In the final part it is shown, that de Sitter space is a factorgroup dS(1, 3) = SO(1,4) SO(1,3) , which is at least from mathematical standpoint much more natural factorization than Poincaré SO(1,3) , which leads to Minkowski. Conformal cyclic cosmology developed by Roger Penrose is briefly described as a motivation for this thesis. This theory could benefit from some properties of de Sitter relativity. 1
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Interaction of test particles with impulsive gravitational waves
Rod, Daniel ; Švarc, Robert (advisor) ; Žofka, Martin (referee)
We summarize methods of construction of spacetimes with nonexpanding impulsive gravitational waves, in particular, limit case of Kundt family including gyratonic spa- cetimes. Subsequently, using C1 -matching procedure leading to refraction formulae of geodesic trajectories crossing the impulsive hypersurfaces, we study behaviour of free test particles. We conduct a physical analysis and a visualisation of geodesic motion for selected spacetimes of our interest. As a part of this work we created a Python pro- gramming language package GRImpulsiveWaves for interactive visualisation of geodesic motion based on refraction formulae. 1
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Physical interpretation of special solutions of Einstein-Maxwell equations
Ryzner, Jiří ; Žofka, Martin (advisor)
In Newtonian physics, it is possible to establish static equilibrium in a system, which consists of extremal sources of gravitational and electromagnetic field. Surprisingly, this situation can occur in general relativity for black holes, too. This work examines a special case involving an infinitely long, straight, extremally charged string, studies its geometry, electrogeodesics, properties of the source and compares the solution to Newtonian physics. We also investigate an analogous situation in a dynamic spacetime with cosmological constant, and we compare it to the static version. Finally, we investigate a periodical solution of Laplace's equation corresponding to infinitely many extremal point sources distributed at regular intervals along a straight line. We study the properties of the electrostatic potential and show that in the limit of large distances from the axis formed by the sources, the solution approaches the charged string. 1
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Selected exact spacetimes in Einstein's gravity
Ryzner, Jiří ; Žofka, Martin (advisor) ; McNutt, David D. (referee) ; Pravdová, Alena (referee)
The aim of this thesis is to construct exact, axially symmetric solutions of Einstein- Maxwell(-dilaton) equations, which possess a discrete translational symmetry along an axis. We present two possible approaches to their construction. The first one is to solve Einstein-Maxwell equations, the second one relies on a dimensional reduction from a higher dimension. We examine the geometry of the solutions, their horizons and singu- larities, motions of charged test particles and compare them. 1
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Regular sources of spacetimes with singularities
Papajčík, Matúš ; Ledvinka, Tomáš (advisor) ; Žofka, Martin (referee)
Since the formulation of Einstein's equations of general relativity, analytical methods were aplied to find their solutions. The complexity and the nonlinear character of the equations meant big difficulty of searching for solutions. Only recently the field of numerical relativity has been developed, which offered a much wider means of research of the properties o these equations. In this thesis we firstly solved the problem of regularization of newtonian sin- gular potential by the method of binding potentials. Next we aplied the methods in general theory of relativity, where we found a suitable source and its pressu- res of the same spherically symmetrical problem. Further we investigated this known Schwarzschild solution in Weyl coordinates for better understanding and comparison of Bonnor's results.
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Physics of extended objects in strong gravitational fields
Veselý, Vítek ; Žofka, Martin (advisor) ; Loukes Gerakopoulos, Georgios (referee)
We study several different models of extended bodies in gravitational fields. Firstly, we revisit the glider model of a dumbbell-like oscillating body. We develop an independent scheme to integrate the equations of motion. We study the radial fall of a Newtonian spring, calculate the position shifts of the spring and find the critical value of the spring constant which cannot overcome the tidal forces. We argue that the relativistic glider model is unphysical due to its behaviour in the critical regions. Secondly, we show that Dixon's theory of extended bodies predicts a geodesic motion of the centre of mass in maximally symmetric spacetimes. We prove that a system of test particles can be described by a conserved stress-energy tensor and we evaluate the position shifts of the glider model in the maximally symmetric spacetimes, showing its disagreement with Dixon's theory. We thus conclude again that the glider model must be rejected. And thirdly, we study a model of an extended body consisting of interacting particles, which is in accord with Dixon's theory. We calculate the position shifts for this model and show that the model does not predict any measurable swimming effect. Finally, we estimate the numerical error of the calculation by finding the position shifts of the model in maximally symmetric...
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Coordinate choice in the Oppenheimer-Snyder model of gravitational collapse
Honsa, Lukáš ; Ledvinka, Tomáš (advisor) ; Žofka, Martin (referee)
The thesis investigate a simple model of a gravitational collapse. The mo- del considers a dust of constant density and zero pressure. In the first part of the thesis we cogitate over well known analytical description of the model under investigation. We elucidate the more difficult mathematical steps and the more complicated parts of general relativity. In the second part of the thesis we con- struct coordinates which cover both the collapsing dust and the outer parts of space - vacuum. We discuss interesting aspects of general relativity portrayed by the chosen description. 1
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Physical interpretation of special solutions of Einstein-Maxwell equations
Ryzner, Jiří ; Žofka, Martin (advisor)
In Newtonian physics, it is possible to establish static equilibrium in a system, which consists of extremal sources of gravitational and electromagnetic field. Surprisingly, this situation can occur in general relativity for black holes, too. This work examines a special case involving an infinitely long, straight, extremally charged string, studies its geometry, electrogeodesics, properties of the source and compares the solution to Newtonian physics. We also investigate an analogous situation in a dynamic spacetime with cosmological constant, and we compare it to the static version. Finally, we investigate a periodical solution of Laplace's equation corresponding to infinitely many extremal point sources distributed at regular intervals along a straight line. We study the properties of the electrostatic potential and show that in the limit of large distances from the axis formed by the sources, the solution approaches the charged string. 1
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