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Advances in Astronomy
Volume 2012 (2012), Article ID 846875, 15 pages
http://dx.doi.org/10.1155/2012/846875
Review Article

The Role of Gravitational Instabilities in the Feeding of Supermassive Black Holes

Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, Milano, Italy

Received 28 August 2011; Accepted 7 October 2011

Academic Editor: Francesco Shankar

Copyright © 2012 Giuseppe Lodato. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

I review the recent progresses that have been obtained, especially through the use of high-resolution numerical simulations, on the dynamics of self-gravitating accretion discs. A coherent picture is emerging, where the disc dynamics is controlled by a small number of parameters that determine whether the disc is stable or unstable, whether the instability saturates in a self-regulated state or runs away into fragmentation, and whether the dynamics is local or global. I then apply these concepts to the case of AGN discs, discussing the implications of such evolution on the feeding of supermassive black holes. Nonfragmenting, self-gravitating discs appear to play a fundamental role in the process of formation of massive black hole seeds at high redshift ( 𝑧 10–15) through direct gas collapse. On the other hand, the different cooling properties of the interstellar gas at low redshifts determine a radically different behaviour for the outskirts of the accretion discs feeding typical AGNs. Here the situation is much less clear from a theoretical point of view, and while several observational clues point to the important role of massive discs at a distance of roughly a parsec from their central black hole, their dynamics is still under debate.