  Three sets of HST+COSTAR FOS and FOC observations provide strong evidence
that the nuclear disk in M87 is in Keplerian rotation around a black hole with
a mass of (2 - 3)x10^9 M_sol. A deep (6 orbits), high resolution H-alpha+[NII]
PC2 HST image shows a trailing, three arm spiral superposed on the underlying
nuclear disk. Several of the extended filaments appear to connect directly to
the disk. The filaments extending to the NW appear to be twisted, as in NGC
4258. Earlier arguments that the NW filaments are flowing from the nucleus are
supported by the presence of blue shifted non-Keplerian components within 20 pc
of the nucleus. The gas in the blue and red shifted non-Keplerian components
has negative energy and will fall back into the nucleus. The morphological and
kinematical observations can be explained by assuming that the filaments
originate in a bidirectional wind from the disk. Such a wind will carry away
angular momentum, enabling gas in the disk to move toward the black hole.
  Small (r ~ 1"; r ~ 100-200 pc), well-defined dusty (D-type) and ionized
(I-type) "nuclear" disks are common in elliptical galaxies. We suggest that the
size of the black hole's radius of influence R_BH relative to the radius of the
nuclear disk R_disk determines whether the disk will be a D-type or I-type.
I-type disks (M87 and M81) occur when R_BH > R_disk. Differential Keplerian
rotation throughout the disk may then generate turbulence and shocks that
ionize the gas. D-type disks (NGC 4261 and NGC 6251) occur when R_BH << R_disk.
The regions of a disk that are exterior to R_BH will rotate at approximately
constant angular velocity in the galaxy's potential, shocks will be suppressed,
and the gas will remain cold and dusty. Intermediate D/I types (3C264) may
occur when R_BH is a significant fraction of the disk's radius.
