|
|
Kozai-Lidov mechanism in post-Newtonian approximation of the general relativity
Smorada, Jakub ; Šubr, Ladislav (advisor) ; Haas, Jaroslav (referee)
In two body systems, the orbit of the particle orbiting the dominant body is, during one orbit, approximately a keplerian ellipse. If the system contains a third, perturbing, body, orbital elements of the orbit of the test particle start to periodically evolve. This process, called Kozai-Lidov mechanism, leads to the closest approaches of the test particle to the dominant body of the system. In this work, I study these closest approaches and their difference between newtonian mechanics and postnewtonian approximation of general relativity. 1
|
|
|
Shell galaxies
Ebrová, Ivana ; Jungwiert, Bruno (advisor) ; Bomans, Dominik J. (referee) ; Combes, Francoise (referee) ; Šubr, Ladislav (referee)
Title: Shell galaxies Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of- sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy during the shell formation in the framework of a simulation with test particles. The...
|
|
|
Chaotic Motion around Black Holes
Suková, Petra ; Semerák, Oldřich (advisor) ; Šubr, Ladislav (referee) ; Loukes-Gerakopoulos, Georgios (referee)
As a non-linear theory of space-time, general relativity deals with interesting dynamical systems which can be expected more prone to chaos than their Newtonian counter-parts. In this thesis, we study the dynamics of time- like geodesics in the static and axisymmetric field of a Schwarzschild black hole surrounded, in a concentric way, by a massive thin disc or ring. We reveal the rise (and/or decline) of geodesic chaos in dependence on parameters of the sys- tem (the disc/ring mass and position and the test-particle energy and angular momentum), (i) on Poincaré sections, (ii) on time series of position and their power spectra, (iii) by applying two simple yet powerful recurrence methods, and (iv) by computing Lyapunov exponents and two other related quantifiers of or- bital divergence. We mainly focus on "sticky" orbits whose different parts show different degrees of chaoticity and which offer the best possibility to test and compare different methods. We also add a treatment of classical but dissipative system, namely the evolution of a class of mechanical oscillators described by non-standard constitutive relations.
|
|
|
Evolution of the stellar disc in the Galactic centre
Kobrle, Stanislav ; Šubr, Ladislav (advisor) ; Karas, Vladimír (referee)
In this thesis we will study dynamical models of Galactic centre analyse them and compare with available observational data. Our main target is to investigate origin of young stars which are being observed here. We examine if they could have been born in a single accretion disc. Next target is to confirm or disprove the possibility of existence one or more disc-like structures which are frequently discussed by scientists. We introduce methods used to detect stellar structures and apply them to artificial and observational data.
|
|
|
Particle motion in the vicinity of compact stellar objects
Čechura, Jan ; Hadrava, Petr (advisor) ; Šubr, Ladislav (referee)
In this thesis we discuss the properties of a radiation-driven stellar wind in an X-ray binary system. Using the parameters appropriate for the high mass Xray binary system Cygnus X-1, the effects of the compact companion on the stellar wind are examined. We have developed a full 3D hydrodynamic model of circumstellar mass based on a modified version of the Castor, Abbott & Klein line-driven mechanism. The effects of the compact companion - gravity and continuum radiation pressure - as well as the centrifugal and Coriolis force due to orbital motion are included. These forces subvert the spherical symmetry of the wind and lead to significantly different results then previous strictly radial hydrodynamic simulations.
|
|
|
Dynamics of young stars in the Galactic nucleus
Haas, Jaroslav ; Šubr, Ladislav (advisor) ; Mayer, Pavel (referee)
As observations show, there are two coherently rotating structures of a few tens of young stars in the centre of our Galaxy close to a supermassive black hole. One of them contains a very dense star cluster, so-called complex IRS 13E. There are some speculations there might be an intermediate mass black hole with mass of the order of 103 -104 M in its centre. Using numerical simulations of the stellar dynamics in the dominant potential of Sgr A* disturbed by IRS 13E and a spherically symmetric cluster of old stars, which is believed to be there too, I have set upper limits on the masses of both disturbers, which guarantee, that the disturbers' presence cannot be of a destructive inuence on observed conguration of the system. It comes out that the incidence of the spherically symmetric star cluster is very stabilizing. My results show that the upper mass limit of the IRS 13E can be an order of magnitude higher, when the spherical cluster is considered (6 × 104 M) in comparison to the case, when it is omitted (4,5 × 103 M).
|
|
|
Shell galaxies: kinematical signature of shells, satellite galaxy disruption and dynamical friction
Ebrová, Ivana ; Jungwiert, Bruno (advisor) ; Šubr, Ladislav (referee) ; Šolc, Martin (referee)
Title: Shell galaxies: kinematical signature of shells, satellite galaxy disruption and dynamical friction Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of-sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy...
|
|
|
Formation and evolution of dynamical binaries
Pavlík, Václav ; Šubr, Ladislav (advisor) ; Heyrovský, David (referee)
The aim of this work is the study of hard binary stars in the star cluster and their time of life before they crossed the energetic boundary, which separates the soft and hard binaries. We used our own method of identification of binary stars within the model of star cluster which is based on the given positions, velocities and masses of stars. This method uses three main criteria -- the proximity of two stars, the time that this pair was found together and negative total energy. The results that we obtained using our algorithm helped us to determie more precise boundary between the hard and soft binary than the analytical estimates based on the evaluation of the typical kinetic energy of the free stars within the cluster. We also studied the lifetime of the binaries before they become hard and we reached a correspondence with the results of Tanikawa et al. (2011), who studied similar topic. Due to a large set of numerical realizations, which we analysed, we got better statistics than previous works. We also found that the examined lifetime of binaries seems to be represented by exponential distribution. For better analysis of this distribution it would be necessary to use about five times higher time resolution than we worked with.
|
|
|
The influence of the stellar mass-loss on the dynamics of star clusters
Dinnbier, František ; Jungwiert, Bruno (advisor) ; Šubr, Ladislav (referee)
This work aims at studying the influence of the stellar mass-loss, resulting from the stellar evolution, on the dynamics of massive star clusters. The emphasis has been put on the mass-loss by low-mass and intermediate-mass stars (m < 8 Mo) that form, at the end of their life, a planetary nebula. The expansion speed of gas released by these stars is lower than the escape speed from sufficiently massive star clusters, and the gas can be retained by the cluster. For modelling of the gas hydrodynamics, a simple sticky-particles method was used. To carry out simulations in which gaseous and stellar particles mutually interact through their gravity, substantial modifications had to be realized in the N-body codes Nbody6 and Hermit. For the sake of comparing the influence of stellar mass-loss and relaxation processes, which are happening in the simplified model, two types of simulations were performed: one with the formation of gaseous particles and the other consisting of purely stellar component. The simulations in which the gas component was present showed out a significantly different evolution in the central part of the cluster than those in which the presence of gas was not considered.
|
|
| |
guest ::
