Inertial-Acoustic Oscillations in Black Hole Accretion Disks

Luminosity variations are common features of black holes in binary systems. It is likely that these variations are due to the physics of the accretion process. In this thesis, we study the possibility that inertial-acoustic oscillations in optically thick black hole accretion disks can produce luminosity variations on dynamical timescales. One and two-dimensional radiation hydrodynamic simulations have been used to study these oscillations. We find that global oscillations are possible at the maximum epicyclic frequency in the disk and local oscillations are possible at the local epicyclic frequencies. The global oscillations can produce rms luminosity variations of \lapprox 0.8% and their existence depends in detail on physical conditions in the system. For a small range (which is viscosity dependent) of accretion rates, strong global oscillations exist. These global oscillations produce strong peaks in luminosity power spectra with a full width at half maximum (in Hz) of approximately one-twelfth of the peak frequency. The local oscillations produce rms luminosity variations of \lapprox 1 and continuum spectral slopes between 0.80 and 1.95 with the flattest slopes corresponding to the strongest oscillations. We find that both local and global oscillations are favored for low accretion rates and large viscosities. We have observed qualitatively similar behavior for disks described by an alpha law or a constant for the kinematic viscosity (\nu) and we predict that oscillations may be present for a restricted range of parameters for any viscosity law in which the shear viscosity (\mu=\rho\nu) increases upon compression. We also find that the results are relatively mass independent when accretion rate (relative to the Eddington accretion rate) and viscosity are held fixed. We conclude that these oscillations may be detectable by the recently launched X-ray Timing Explorer.