Related papers: AGN Light Echoes and the Accretion Disc Self-Gravi…
We consider the Comptonisation of the photons that make up the relativistically blurred reflection that is commonly detected from the accretion discs of AGN by the coronae of energetic particles believed to give rise to the powerful X-ray…
We reexamine the hypothesis that the optical/UV/soft X-ray continuum of Active Galactic Nuclei is thermal emission from an accretion disk. Previous studies have shown that fitting the spectra with the standard, optically thick and…
Although accretion disks are a theoretically appealing model for the geometry and dynamics of the gas in the vicinity of black holes in Active Galactic Nuclei (AGN), there is little direct observational evidence for their existence. The…
We present our latest results on the connection between accretion rate and relativistic jet power in AGN, by using a large sample which includes mostly blazars, but contains also some radio--galaxies. The jet power can be traced by…
We discuss two important instability mechanisms that may lead to the limit-cycle oscillations of the luminosity of the accretion disks around compact objects: ionization instability and radiation-pressure instability. Ionization instability…
The time-scales of the variabilities in changing look (CL) active galactic nuclei (AGNs) are usually at the order of years to tens of years (some of them are even shorter than one year), which are much shorter than the viscous timescale of…
We analyze the broadband photometric light curves of Seyfert 1 galaxies from the Sergeev et al. (2005) sample and find that a) perturbations propagating across the continuum emitting region are a general phenomenon securely detected in most…
Here we discuss the effects of strong gravity that can be observed in electromagnetic spectra of active galactic nuclei (AGN). According to the unification model of an AGN, there is a supermassive black hole ($10^7 - 10^9 M_\odot$) in its…
Both long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nuclei (AGN) accretion disks. As these bursts propagate through the disks they live in, they photoionize the medium causing…
(Abridged) The Galactic Center (GC) hosts a population of young stars some of which seem to form mutually inclined discs of clockwise and counter clockwise rotating stars. We present a warped disc origin scenario for these stars assuming…
A major amendment in recent models of hierarchical galaxy formation is the inclusion of so-called AGN feedback. The energy input from an active central massive black hole is invoked to suppress star formation in early-type galaxies at later…
(Abridged) Narrow Line Seyfert 1 (NLS1) galaxies have low mass black holes and mass accretion rates close to (or exceeding) Eddington, so a standard blackbody accretion disc should peak in the EUV. However, the lack of true absorption…
Stars and compact objects embedded in accretion disks of active galactic nuclei (AGNs), dubbed as ``accretion-modified star" (AMS), often experience hyper-Eddington accretion in the dense gas environment, resulting in powerful outflows as…
Observations have shown that the Eddington ratios (the ratio of the bolometric luminosity to the Eddington luminosity) in QSOs/active galactic nuclei (AGNs) cover a wide range. In this paper we connect the demography of AGNs obtained by the…
We propose a scenario in which massive stars form in a self-gravitating gaseous disc around a supermassive black hole. We find that once the surface density of the disc exceeds a critical value, the disc fragments into dense clumps. The…
Super-Eddington accretion discs with 3 and 15 dot M_E around black holes with mass 10 M_sun are examined by two-dimensional radiation hydrodynamical calculations extending from the inner disc edge to 5*10^4 r_g and lasting up to \sim 10^6…
Sgr A* is extra-ordinarily dim in all wavelengths requiring a very low accretion rate at the present time. However, at a radial distance of a fraction of a parsec from Sgr A*, two rings populated by young massive stars suggest a recent…
Pouliasis et al (2022b) explored star formation rates, black hole accretion rates, and stellar mass of active galaxies at redshift above 3.5, uncovering a leveling off of the star formation rate at high stellar mass, which they consider to…
Young massive stars warm up the large amount of gas and dust which condenses in their vicinity, exciting a forest of lines from different molecular species. Their line brightness is a diagnostic tool of the gas physical conditions locally,…
The Keplerian motion of accretion disks in Active Galactic Nuclei (AGN) is usually believed to be generated by a heavy central mass. We investigate accreting disk systems with polytropic gas in Keplerian rotation and obtain a…