  Radiation pressure-dominated accretion disks are predicted to exhibit strong
density inhomogeneities on scales much smaller than the disk scale height, due
to the nonlinear development of photon bubble instability. Radiation would
escape from such a "leaky" disk at a rate higher than that predicted by
standard accretion disk theory. The disk scale height is then smaller than that
of a similar disk without small-scale inhomogeneities, and the disk can remain
geometrically thin even as the flux approaches and exceeds the Eddington limit.
An idealized one-zone model for disks with radiation-driven inhomogeneities
suggests that the escaping flux could exceed L_E by a factor of up to ~10-100,
depending on the mass of the central object. Such luminous disks would develop
strong mass loss, but the resulting decrease in accretion rate would not
necessarily prevent the luminosity from exceeding L_E. We suggest that the
observed "ultraluminous X-ray sources" are actually thin, super-Eddington
accretion disks orbiting stellar-mass black holes, and need not indicate the
existence of a class of intermediate-mass black holes.
