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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
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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).
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Symmetries and dynamics of star clusters
Haas, Jaroslav ; Šubr, Ladislav (advisor) ; Baumgardt, Holger (referee) ; Jungwiert, Bruno (referee)
We investigate the orbital evolution of an initially thin stellar disc around a supermassive black hole, considering various perturbative sources of gravity. By means of direct numerical N-body modelling, we first focus on the case when the disc is embedded in an extended spherically symmetric star cluster. We find that the gravitational influence of the disc triggers formation of macroscopic non- spherical substructure in the cluster which, subsequently, significantly affects the evolution of the disc itself. In another approximation, when the cluster is emu- lated by an analytic spherically symmetric potential, we further consider pertur- bative gravitational influence of a distant axisymmetric source. Using standard perturbation methods, we derive a simple semi-analytic model for such a config- uration. It turns out that the additional axisymmetric potential leads to mutual gravitational coupling of the individual orbits from the disc. Consequently, the dense parts of the disc can, for some period of time, evolve coherently. Finally, we apply some of our results to the young stellar disc which is observed in the innermost parsec of the Galactic Centre. 1
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Numerical analysis of the Hills mechanism
Čížek, Kryštof ; Haas, Jaroslav (advisor) ; Brož, Miroslav (referee)
Interaction of three bodies is generally quite chaotic and a problem difficult to solve. Case in which binary star approaches third, heavier body is a special configuration of this problem and was investigated by J. G. Hills in his articles. In such interaction, either absolute breakup of the system to three independent bodies, survival of the binary star, or replacement of one component of the binary by the heavier body would occur - an exchange collision. If the replacement is to happen, the exchanged body is ejected away from the system with high velocity and such effect we call Hills mechanism. In such case the binary star usually has higher binding energy and is much more resistant if such situation were to occur again. However, Hills' results are not sufficient e.g. for effects within the core of our galaxy. Using numerical integration we modelled approximations of binary stars to a third, heavier body, thanks to which we could verify Hills' results and expand on them with initial conditions which are more suited to situations occuring within the core of our galaxy.
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Symmetries and dynamics of star clusters
Haas, Jaroslav
We investigate the orbital evolution of an initially thin stellar disc around a supermassive black hole, considering various perturbative sources of gravity. By means of direct numerical N-body modelling, we first focus on the case when the disc is embedded in an extended spherically symmetric star cluster. We find that the gravitational influence of the disc triggers formation of macroscopic non- spherical substructure in the cluster which, subsequently, significantly affects the evolution of the disc itself. In another approximation, when the cluster is emu- lated by an analytic spherically symmetric potential, we further consider pertur- bative gravitational influence of a distant axisymmetric source. Using standard perturbation methods, we derive a simple semi-analytic model for such a config- uration. It turns out that the additional axisymmetric potential leads to mutual gravitational coupling of the individual orbits from the disc. Consequently, the dense parts of the disc can, for some period of time, evolve coherently. Finally, we apply some of our results to the young stellar disc which is observed in the innermost parsec of the Galactic Centre. 1
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Spatial distribution of the young stars observed in the centre of the Milky Way
Kepčija, Petr ; Haas, Jaroslav (advisor) ; Šubr, Ladislav (referee)
Galactic centre of Milky way is one of its most exotic parts. Right in the centre there lies a black hole, which has a mass of several million masses of our Sun. In the vicinity of this black hole there was recently found a young star cluster. The origin of these stars remains a mystery. Their spatial arrangement in a disc can give us a clue. The result of this thesis is a thorough analysis of the existence of two discs of young stars using the data from VLT telescopes in Chile and Keck telescopes in Hawaii. The analysis confirms the existence of one disc and shows the existence of the other disc seems to be very probable. 1
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Numerical analysis of the Hills mechanism
Čížek, Kryštof ; Haas, Jaroslav (advisor) ; Brož, Miroslav (referee)
Interaction of three bodies is generally quite chaotic and a problem difficult to solve. Case in which binary star approaches third, heavier body is a special configuration of this problem and was investigated by J. G. Hills in his articles. In such interaction, either absolute breakup of the system to three independent bodies, survival of the binary star, or replacement of one component of the binary by the heavier body would occur - an exchange collision. If the replacement is to happen, the exchanged body is ejected away from the system with high velocity and such effect we call Hills mechanism. In such case the binary star usually has higher binding energy and is much more resistant if such situation were to occur again. However, Hills' results are not sufficient e.g. for effects within the core of our galaxy. Using numerical integration we modelled approximations of binary stars to a third, heavier body, thanks to which we could verify Hills' results and expand on them with initial conditions which are more suited to situations occuring within the core of our galaxy.
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The Young Star Clusters in the Galactic Centre
Jakš, Sebastian ; Haas, Jaroslav (advisor) ; Kroupa, Pavel (referee)
In addition to three massive star clusters - Arches, Quintuplet, Nuclear Star Cluster - the Galactic Centre hosts a significant number of isolated stars. It has been proposed that at least some of these stars were formed inside one of the three clusters and, subsequently, ejected out of them during their dynamical evolution. In this work, I investigate the dependence of this complex dynamical process for the Arches cluster upon its unknown line-of-sight distance by means of numerical N-body modelling. It turns out that both the dissipation rate of the Arches and spatial distribution of the ejected stars differs significantly if various values of the line-of-sight distance are considered. In the context of this finding, I critically evaluate the approach of Habibi et al. (2014) who assumed the Arches cluster to be 100 pc in front of the Galactic Centre when modelling its contribution to the observed isolated stars. 1
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Awareness of the students at the elementary school in the issue of drugs
HAAS, Jaroslav
Aim of this bachelor's thesis is to assess what level of drug awareness and knowledge pupils at second stage of elementary school have. The thesis is divided into two main parts. The first part is theoretical and covers the history and present of the drug scene, basic terminology, types of drugs, their effects and risks. Afterwards drug abuse signs and risk factors for addiction are described. This part of the thesis focuses also on a drug prevention, mainly in school education. The second, practical part presents two chosen schools (Elementary School in Domažlice, Komenského 17 and Elementary school in Mrákov) and their drug prevention programs (describing their forms, methods and cooperation with external specialists). Based on quantitative methodology, a survey was conducted to assess the drug awareness and knowledge (incl. alcohol and cigarettes) of 8th and 9th grade pupils of above mentioned schools. The survey was also focused on how well pupils are able to evaluate the risk of drug use and what attitude towards drugs they have.
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Tidal disruption in the vicinity of black holes in active galaxies
Štolc, Marcel ; Svoboda, Jiří (advisor) ; Haas, Jaroslav (referee)
In this thesis we studied tidal disruptions of stars in the vicinity of com- pact objects and performed spectral re-analysis of XMMSL1 J074008.2-853927, one of the most prominent candidates of tidal disruption events (TDE) around super-massive black holes. This particular TDE shows signs of thermal and non- thermal radiation component and is also indicating the energy excess correspond- ing to the iron line emission of Fe Kα line. We analysed X-ray spectra from two XMM-Newton observations - from the 30-th of April 2014 and the 12-th of Jan- uary 2015 that were follow-up observations after the discovery of this TDE. We confirmed the possible thermal and non-thermal profile of radiation and the pres- ence of Fe Kα line in the data of the first XMM-Newton follow-up observation. We studied in detail the parameters of the iron line, which cannot be to tightly constrained due to insufficient quality of data. However, we also showed that in case of modelling the excess in lower energy band with relativistic reflection the parameters can be constrained. 1
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