Normal Modes of Black Hole Accretion Disks
  This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and show for the first time that modes covering the whole extension of the disk (full--disk p--modes) can exist within the studied thin disk model. However, these modes have relatively short wavelengths. 
Manuel Ortega-Rodriguez, Alexander S. Silbergleit, Robert V. Wagoner