well as a short timescale for the growth of the seed. In fact, numerical simulations suggest that after the merger of two galaxies, a considerable amount of gas is settled into the central region of the resulting object. The gas loses angular momentum in a timescale comparable to the dynamical timescale (Mihos & Hernquist 1996; Barnes 2002), forming circumnuclear self-gravitating disks having masses in the range $10^6 - 10^9 ~ M_\odot$ and dimensions of about 100 - 500 pc.

Massive accretion disks are, in general, self-gravitating in their early evolutionary phases, a situation that affects the usual dynamics of disks controlled only by the gravitational forces due to the central body. In fact, models of non steady self-gravitating accretion disks were computed by Montesinos & de Freitas Pacheco (2011, hereafter MP11) satisfying the aforementioned requirements or, in other words, they are luminous enough and they permit the growth of seeds in a short timescale, consistent with observations of bright QSOs at high $z$. Some aspects of the work by those authors will be shortly reviewed below, followed by the presentation of new results.

As mentioned before, the very early formation of a massive disk in the central region of a 