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Coherent dusty and gaseous structures near the Galactic center
Štofanová, Lýdia ; Karas, Vladimír (advisor) ; Kovář, Jiří (referee)
Sagittarius A*, a compact source in the centre of the Milky Way, is the nearest supermassive black hole (SMBH) in our cosmic neighbourhood, where various astrophysical processes take place. In consequence, variety of structures emerge near the Galactic centre and bow shocks that are closely studied in this work represent an example of them. The introductory part of this thesis is a brief review of the history of the Galactic centre research and its discovery in radio wavelengths. The main body of the thesis is focused on a simplified model of the bow- shock structures that are generated by stars moving supersonically with respect to the ambient medium. We discuss how these structures vary along the orbit. To this end, we consider four different models: (a) without the presence of any gaseous medium emerging from or accreting onto the SMBH, (b) taking an outflow from the SMBH into account, (c) the case of an inflow onto the SMBH, and finally (d) the combined model involving both an outflow and an inflow at the same time. We discuss symmetries of each model (or lack of them) and we find that the model considering the ambient medium at rest appears symmetrical with respect to the pericentre passage. The combined model manifests itself as the most asymmetrical one of them all. We show profiles for the...
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Coherent dusty and gaseous structures near the Galactic center
Štofanová, Lýdia ; Karas, Vladimír (advisor) ; Kovář, Jiří (referee)
Sagittarius A*, a compact source in the centre of the Milky Way, is the nearest supermassive black hole (SMBH) in our cosmic neighbourhood, where various astrophysical processes take place. In consequence, variety of structures emerge near the Galactic centre and bow shocks that are closely studied in this work represent an example of them. The introductory part of this thesis is a brief review of the history of the Galactic centre research and its discovery in radio wavelengths. The main body of the thesis is focused on a simplified model of the bow- shock structures that are generated by stars moving supersonically with respect to the ambient medium. We discuss how these structures vary along the orbit. To this end, we consider four different models: (a) without the presence of any gaseous medium emerging from or accreting onto the SMBH, (b) taking an outflow from the SMBH into account, (c) the case of an inflow onto the SMBH, and finally (d) the combined model involving both an outflow and an inflow at the same time. We discuss symmetries of each model (or lack of them) and we find that the model considering the ambient medium at rest appears symmetrical with respect to the pericentre passage. The combined model manifests itself as the most asymmetrical one of them all. We show profiles for the...
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Astrophysical processes near a galactic centre
Hamerský, Jaroslav ; Karas, Vladimír (advisor) ; Kulhánek, Petr (referee) ; Janiuk, Agnieszka (referee)
An accretion torus is an important astrophysical phenomenon which is be- lieved to account for various features of mass inflow and release of radiation on diverse scales near stellar-mass as well as supermassive black holes. When the stationary torus is perturbed it starts to oscillate and once some part of the torus overflows the closed equipotential surface, defined by the stationary solution, this material is accreted or ejected. These oscillations reveal both spacetime properties and the intrinsic characteristics of the torus model. We study the oscillation and accretion properties of geometrically thick accretion tori using general relativistic magnetohydrodynamic simulations. Assuming axial symmetry these simulations are restricted to 2-D approximation. We discuss the impact of the presence of the large scale magnetic field and the profile of the specific angular momentum on the oscillation properties and on the accretion flow motion. 1
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Infrared-excess Source DSO/G2 Near the Galactic Center: Theory vs. Observations
Zajaček, M. ; Eckart, A. ; Peissker, F. ; Karssen, G. ; Karas, Vladimír
Based on the monitoring of the Dusty S-cluster Object (DSO/G2) during its closest approach to the Galactic Center supermassive black hole in 2014 and 2015 with ESO VLT/SINFONI, we further explore the model of a young, accreting star to explain observed spectral and morphological features. The stellar scenario is supported by our ndings, i.e., ionized-hydrogen emission from the DSO that remains spatially compact before and after the peribothron passage. The detection of DSO/G2 object as a compact single-peak emission-line source is not consistent with the original hypothesis of a core-less cloud that is necessarily tidally stretched, hence producing a double-peak emission line prole around the pericentre passage. This strengthens the evidence that the DSO/G2 source is a dust-enshrouded young star that appears to be in an accretion phase. The infall of material from the circumstellar disc onto the stellar surface can contribute signicantly to the emission of Br line as well as the observed large line width of the order of 10 angstrom.
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