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C.K. Chan, D. Psaltis (Physics Department, U. Arizona)
Although quasi-periodic oscillations have been discovered in different X-ray sources, their origin is still a matter of debate. Analytical studies of viscous accretion disks have shown three types of trapped global modes with properties that appear to agree with the observations. However, these studies take only linear effect into account and do not address issues of mode excitation and decay. Moreover, recent observations of QPOs in black holes strongly suggest that resonance between modes plays a crucial role. Studying the excitation and interaction between modes demands a high-accuracy numerical algorithm. We have developed a two-dimensional, pseudo-spectral algorithm in order to model MHD flows around accreting black holes. In this first study of the inner regions of viscous accretion disks, we find that the flow inside the innermost stable circular orbit is unstable to non-axisymmetric perturbations. Spiral waves appear in the simulation and provide a plausible explanation of the high-frequency QPOs observed from accreting black holes.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.