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Accretion discs in the context of tidal disruption of stars in nuclei of galaxies
Štolc, Marcel ; Karas, Vladimír (advisor) ; Schee, Jan (referee)
Stars can be stretched and ripped apart by the super-massive black hole at the core of a galaxy. The remnant gaseous trail gradually circularizes in a ring of mass that spreads by the viscous forces into an accretion disc. In this thesis we have studied the spectral line profle time evolution of radiation refected by the accretion disc located around a super-massive black hole. We assume the central body to be a slowly rotating or non-rotating super-massive black hole with no charge, in the frst approximation represented by the Schwarzschild solution. In a sense of Shakura-Sunyaev standard accretion disc model with the kinematic viscosity parameter α ≈ 1 we allow the accretion disc evolution to be guided by the angular momentum transfer equation with the initial mass ring located at the tidal radius being the product of tidal disruption of a star passing by a super-massive black hole. During the simulations we keep varying the mass of the central body while we keep the mass and the radius of the star constant (M = 1M⊙ and R = 1R⊙), i.e. taking into account the solar-type stars only. We defer the prospects of the full analysis involving spin (and charge) of the central body for the future study as it will be necessary to use the equations for the redshift factor and the accretion disc evolution...
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Accretion discs in the context of tidal disruption of stars in nuclei of galaxies
Štolc, Marcel ; Karas, Vladimír (advisor)
Stars can be stretched and ripped apart by the super-massive black hole at the core of a galaxy. The remnant gaseous trail gradually circularizes in a ring of mass that spreads by the viscous forces into an accretion disc. In this thesis we have studied the spectral line profle time evolution of radiation refected by the accretion disc located around a super-massive black hole. We assume the central body to be a slowly rotating or non-rotating super-massive black hole with no charge, in the frst approximation represented by the Schwarzschild solution. In a sense of Shakura-Sunyaev standard accretion disc model with the kinematic viscosity parameter α ≈ 1 we allow the accretion disc evolution to be guided by the angular momentum transfer equation with the initial mass ring located at the tidal radius being the product of tidal disruption of a star passing by a super-massive black hole. During the simulations we keep varying the mass of the central body while we keep the mass and the radius of the star constant (M = 1M⊙ and R = 1R⊙), i.e. taking into account the solar-type stars only. We defer the prospects of the full analysis involving spin (and charge) of the central body for the future study as it will be necessary to use the equations for the redshift factor and the accretion disc evolution...
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Missing bright red giants in the Galactic center: A fingerprint of its once active state?
Zajaček, Michal ; Araudo, Anabella ; Karas, Vladimír ; Czerny, B. ; Eckart, A. ; Suková, Petra ; Štolc, Marcel ; Witzany, V.
We propose a novel scenario for the bright red-giant depletion based onthe collisions between red giants and the nuclear jet, which was likely active in the Galactic center a few million years ago and could have led to the formation of the large-scaleγ-ray Fermi bubbles. The process of the jet-induced ablation of red giants appears to be most efficient within∼0.04 pc(S-cluster), while at larger distances it was complemented by star–accretion disc collisions and at smaller scales, tidal stripping operated. These three mechanisms likely operated simultaneously and createdan apparent core of late-type stars within∼0.5 pc.
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From gappy to ringed: signatures of an accretion disk radial structure in profiles of the reflection line
Štolc, Marcel ; Zajaček, M. ; Karas, Vladimír
We focus on the theoretical profiles of a spectral line produced by reflection of the surface of both gappy accretion disk and a ring-like structure near a black hole. We describe the relativistic effects in an approximative manner. While a smooth accretion disk leads to a typical, double-horn shape with unequal wings due to Doppler boosting and an additional peak due to the lensing amplification at high inclination angle, the gaps and rings give rise to a more complex dependence which reflects the location and the radial extent of the inhomogeneities in the accretion flow.
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Accretion discs in the context of tidal disruption of stars in nuclei of galaxies
Štolc, Marcel ; Karas, Vladimír (advisor) ; Schee, Jan (referee)
Stars can be stretched and ripped apart by the super-massive black hole at the core of a galaxy. The remnant gaseous trail gradually circularizes in a ring of mass that spreads by the viscous forces into an accretion disc. In this thesis we have studied the spectral line profle time evolution of radiation refected by the accretion disc located around a super-massive black hole. We assume the central body to be a slowly rotating or non-rotating super-massive black hole with no charge, in the frst approximation represented by the Schwarzschild solution. In a sense of Shakura-Sunyaev standard accretion disc model with the kinematic viscosity parameter α ≈ 1 we allow the accretion disc evolution to be guided by the angular momentum transfer equation with the initial mass ring located at the tidal radius being the product of tidal disruption of a star passing by a super-massive black hole. During the simulations we keep varying the mass of the central body while we keep the mass and the radius of the star constant (M = 1M⊙ and R = 1R⊙), i.e. taking into account the solar-type stars only. We defer the prospects of the full analysis involving spin (and charge) of the central body for the future study as it will be necessary to use the equations for the redshift factor and the accretion disc evolution...
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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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