  We show that gas in a large fraction of low mass dark matter halos may form
Toomre stable disks, if angular momentum is conserved when the gas contracts.
Such halos would be stable to star formation and therefore remain dark. This
may potentially explain the discrepancy between the predicted and observed
number of dwarf satellites in the Local Group, as well as the deviation between
the predicted and the observed faint end slope of the luminosity function. The
above mechanism does not require a strong variation of the baryon fraction with
the virial mass of the dark halo. We show that model fits to rotation curves
are also consistent with this hypothesis: none of the observed galaxies lie in
the region of parameter space forbidden by the Toomre stability criterion.
