Models of The Active Nucleus
For a long time it has been argued that AGN must be powered by accretion onto massive black holes (with masses between 106 and 1010 times that of the Sun). AGN are both compact and persistently extremely luminous; accretion can potentially give very efficient conversion of potential and kinetic energy to radiation, and a massive black hole has a high Eddington luminosity, so that it can provide the observed high persistent luminosity. Central supermassive black holes are now believed to exist in the centers of most or all massive galaxies: the mass of the black hole correlates well with the velocity dispersion of the galaxy bulge (the M-sigma relation) or with bulge luminosity (e.g.). Thus AGN-like characteristics are expected whenever a supply of material for accretion comes within the sphere of influence of the central black hole.
Read more about this topic: Active Galactic Nucleus
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