Magnetically elevated accretion disks in active galactic nuclei: broad
  emission line regions and associated star formation
  We propose that the accretion disks fueling active galactic nuclei are
supported vertically against gravity by a strong toroidal ($\phi-$direction)
magnetic field that develops naturally as the result of an accretion disk
dynamo. The magnetic pressure elevates most of the gas carrying the accretion
flow at $R$ to large heights $z > 0.1 R$ and low densities, while leaving a
thin dense layer containing most of the mass --- but contributing very little
accretion --- around the equator. We show that such a disk model leads
naturally to the formation of a broad emission line region through thermal
instability. Extrapolating to larger radii, we demonstrate that local
gravitational instability and associated star formation are strongly suppressed
compared to standard disk models for AGN, although star formation in the
equatorial zone is predicted for sufficiently high mass supply rates. This new
class of accretion disk models thus appears capable of resolving two
longstanding puzzles in the theory of AGN fueling: the formation of broad
emission line regions and the suppression of fragmentation thought to inhibit
accretion at the required rates. We show that the disk of stars that formed in
the Galactic Center a few million years ago could have resulted from an episode
of magnetically elevated accretion at $> 0.1$ of the Eddington limit.
