  We present a detailed model for the formation of massive objects at the
centers of galaxies. The effects of supernovae heating and the conditions of
gas loss are revisited. The escape time of the gas is compared with the cooling
time, which provides an additional condition not previously considered. Its
consequences for the allowed mass range of the halo is calculated. It is shown
that sufficient gas is retained to form massive dark objects and quasars even
for moderately massive halos but a decline is expected at low redshifts.
Subsequently, a gaseous disk forms with a radial extent of a ~kpc, spun up by
tidal torques and magnetized by supernovae fields with fields strengths of
$10-100 \mu G$. In a model of a self-similar accretion flow in an initially
dominant halo, it is shown that for typical halo parameters, about $10^8
M_\odot$ accretes via small magnetic stresses (or alternatively by self-gravity
induced instability or by alpha viscosity) in $10^8$ years into a compact
region. A model of a self-gravitating evolution of a compact magnetized disk,
which is relevant when a significant fraction of the disk mass falls in, is
presented, and it has a rapid collapse time scale of a million years. The two
disk solutions, one for accretion in an imposed halo potential and the other
for self-gravitating disk, obtained here, have general utility and can be
adapted to other contexts like protostellar disks as well.
