Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes the accretion flow lead to stochastic variability of this emission on a wide range timescales. We measure observed 67 characteristic timescale which power spectrum flattens. find correlation between hole mass, extending over entire mass...

The properties of relativistic radio jets are thought to be closely connected with the properties of accretion disks in active galactic nuclei. We explore this issue using a sample of 35 blazars with very-long baseline observations, for which we can estimate the kinetic powers of their relativistic jets, the bolometric luminosity of their accretion disks, and the masses of their black holes. Co...

Twenty five years have passed by since models of accretions and jets have separately emerged. Today, it is understood that these two objects are related to each other in a fundamental way. In a binary system, matter from an accretion disk enters into a black hole. A part of it is bounced back because of the centrifugal barrier, radiation pressure or magnetohydrodynamic effects, to form jets and...

We fit X-ray spectral data in the thermal dominant or high soft state of two dynamically confirmed black holes, GRO J1655-40 and 4U 1543-47, and estimate the dimensionless spin parameters a∗ ≡ a/M of the two holes. Our spectral model consists of one principal component, a multitemperature blackbody disk model that includes all general relativistic effects, plus standard low-energy absorption an...

With most physicists and astrophysicists in agreement that black holes do indeed exist, the focus of astrophysical black hole research has shifted to the detailed properties of these systems. Nature has provided us with an extremely useful probe of the region very close to an accreting black hole — X-ray irradiation of relatively cold material in the vicinity of the black hole can imprint chara...

Analytical studies and numerical simulations of time dependent axially symmetric flows onto black holes have shown that it is possible to produce stationary shock waves with a stable position both for ideal inviscid and for moderately viscous accretion disks. We perform several two dimensional numerical simulations of accretion flows in the equatorial plane to study shock stability against non-...

Here we analyze how the angular momenta (spins) of black holes in the centers of Active Galactic Nuclei (AGN) affect the shape of the FeKα line emitted from their accretion disks. For that purpose, we compared the observed line profile in the case of radio galaxy 3C 405 (Cygnus A) with its profiles, obtained by numerical simulations based on ray-tracing method in the Kerr metric. Our results sh...

Galaxy mergers produce supermassive black hole binaries, which emit gravitational waves prior to their coalescence. We perform three-dimensional hydrodynamic simulations to study the tidal disruption of stars by such a binary in the final centuries of its life. We find that the gas stream of the stellar debris moves chaotically in the binary potential and forms accretion disks around both black...

The lack of our knowledge on how angular momentum is transported in accretion disks around black holes has prevented us from fully understanding their high energy emissions. We briefly highlight some theoretical models, emphasizing the energy flow and electron energization processes. More questions and uncertainties are raised from a plasma physics point of view.

We critically assess the role of the Blandford-Znajek mechanism in the powering of outflows from accretion disk-fed black holes. We argue that there is no reason to suppose that the magnetic field threading the central spinning black hole differs significantly in strength from that threading the central regions of the disk. In this case, we show that the electromagnetic output from the inner di...