We propose that massive central objects form in the centers of the bars tha
t must develop in young high surface density galactic disks. Large-scale dy
namics shut off the growth of the central mass before it reaches similar to
2% of the disk mass at the time, but this mass is sufficient to substantia
lly weaken the bar. Subsequent evolution of the galaxy can either complete
the destruction of the bar or cause it to recover, depending on the angular
momentum distribution of later infalling material. We produce massive, ful
ly self-gravitating disks having roughly hat rotation curves that are quite
stable. If at least part of the central masses we require constitute the e
ngines of QSOs, then our picture naturally accounts for their redshift depe
ndence since the fuel supply is shut off by the development of an inner Lin
dblad resonance. A prediction is that massive objects should not be found i
n halo-dominated galaxies such as low-luminosity or low surface brightness
galaxies.