Oscillations of radiation pressure supported tori near black holes

Abstract

We study the dynamics of radiation pressure supported tori around Schwarzschild black holes, focusing on their oscillatory response to an external perturbation. Using KORAL, a general relativistic radiation hydrodynamics code capable of modeling all radiative regimes from the optically thick to the optically thin, we monitor a sample of models at different initial temperatures and opacities, evolving them in two spatial dimensions for $\sim 165$ orbital periods. The dynamics of models with high opacity is very similar to that of purely hydrodynamics models, and it is characterized by regular oscillations which are visible also in the light curves. As the opacity is decreased, the tori quickly and violently migrate towards the gas-pressure dominated regime, collapsing towards the equatorial plane. When the spectra of the $L_2$ norm of the mass density are considered, high frequency inertial-acoustic modes of oscillations are detected (with the fundamental mode at a frequency $68 M_{\rm BH}^{-1}\,\rm Hz$), in close analogy to the phenomenology of purely hydrodynamic models. An additional mode of oscillation, at a frequency $129 M_{\rm BH}^{-1}\,\rm Hz$, is also found, which can be unambiguously attributed to the radiation. The spectra extracted from the light curves are typically more noisy, indicating that in a real observation such modes would not be easily detected.