Accretion Disks in Active Galactic Nuclei

Dear Colleagues,

According to the most widely accepted paradigm, the Active Galactic Nuclei (AGNs) are powered by accretion onto a central, supermassive black hole, which mass scales with the mass of the galactic bulge. There are two general types of accretion solutions proposed throughout the years: A thin, energy-efficient, Sakura-Sunyaev accretion disk and a geometrically thick, hot, advection-dominated flow. Presumably they operate in different types of AGNs, leading to their very different observational appearances in terms of spectral-energy distribution, radio loudness, overall power, etc. Except for this general picture, however, pretty much everything else is a subject to debates. What drives, for instance, the AGN variability and how is it related to the accretion disk structure? How are the outer parts of the disk related to the existence of the Broad Line Region (BLR) and why only objects with thin disks appear to hold such BLRs? How is the inner disk structure is related to the launching and the collimation of powerful jets in some objects and what is the role of the black hole spin in the jet production? Are there transitions between different accretion solutions within the same object? What is the role of the accretion disk winds in shaping the galaxy via feedback mechanisms? What is the role of the accretion for the mass accumulation of the first black holes in high-z AGNs?  Is there a quasar sequence, similar to the stellar Main Sequence and how are the accretion disk’s structure and parameters related to mechanisms driving it?

This Special Issue of Galaxies is dedicated to an attempt to present plausible answers to these and many other open questions, concerning the AGN astrophysics with regard to the accretion disks. World’s leading experts in the field have been invited to present their review papers on the subject. Theoretical, observational, interpretational, and numerical studies are accepted. This issue is intended to facilitate mostly young and new in the field scientists to get acquainted with the newest and, in the same time, the most influential and inspiring achievements in the astrophysics of the accretion disks in AGNs.

Dr. Rumen Bachev
Guest Editor

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