Národní úložiště šedé literatury Nalezeno 4 záznamů.  Hledání trvalo 0.02 vteřin. 
Perturbing the accretion flow onto a supermassive black hole by a passing star
Suková, Petra ; Zajaček, M. ; Witzany, V. ; Karas, Vladimír
The close neighbourhood of a supermassive black hole contains not only accreting gas and dust, but also stellar-sized objects like stars, stellar-mass black holes, neutron stars, and dust-enshrouded objects that altogether form a dense nuclear star-cluster.These objects interact with the accreting medium and they perturb the otherwise quasi-stationary configuration of the accretion flow. We investigate how the passages of a star can influence the black hole gaseous environment with GRMHD 2D and3D simulations. We focus on the changes in the accretion rate and the associated emergence of outflowing blobs of plasma.
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.
Emergence of magnetic null points in electro-vacuum magnetospheres of compact objects: The case of a plunging neutron star
Kopáček, Ondřej ; Tahamtan, T. ; Karas, Vladimír
We study the possible emergence of magnetic null points which are astrophysically relevant for the processes of magnetic reconnection. While the magnetic reconnection occurs in the presence of plasma and may lead to violent mass ejection, we show here that strong gravitation of the supermassive black hole may actively support the process by suit-ably entangling the field lines even in the electro-vacuum description. In this contribution we further discuss the case of a dipole-type magnetic field of the neutron staron the plunging trajectory to the supermassive black hole. While we have previously shown that given model in principle admits the formation of magnetic null points, here we explore whether and where the null points appear for the astrophysically relevant values of the parameters.
Magnetically ejected disks: Equatorial outflows near vertically magnetized black hole
Karas, Vladimír ; Sapountzis, K. ; Janiuk, A.
We show an example of an equatorial outflow driven by a large scale magnetic field. We initiate our computations with a spherically symmetric distribution of gas, which flows on to the domain from a large distance, r R+. After the flow settles in a steady (Bondi) solution, we impose an axially symmetric configuration of a uniform (Wald) magnetic field aligned with the rotation axis of the black hole. Then we evolve the initial configuration numerically by employing the MHD code that approaches the force-free limit of a perfectly conducting fluid. We observe how the magnetic lines of force start accreting with the plasma while an equatorial intermittent outflow develops and goes on ejecting some material away from the black hole.

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