On The Formation of Disk Galaxies and Massive Central Objects
  We propose that massive central objects form in the centers of the bars which must develop in young high-surface density galactic disks. Large-scale dynamics shuts off the growth of the central mass before it reaches $\sim 2%$ of the disk mass at the time, but this mass is sufficient to weaken the bar substantially. Subsequent evolution of the galaxy can either complete the destruction of the bar or cause it to recover, depending upon the angular momentum distribution of later infalling material. We produce massive, fully self-gravitating disks having roughly flat rotation curves which are quite stable. If at least part of the central masses we require constitute the engines of QSOs, then our picture naturally accounts for their redshift dependence, since the fuel supply is shut off by the development of an inner Lindblad resonance. A prediction is that massive objects should not be found in halo dominated galaxies, such as low-luminosity, or low-surface brightness galaxies. 
J. A. Sellwood and E. M. Moore (Rutgers University)