Sawtooth-like oscillations of black hole accretion disks

Details Sawtooth-like oscillations of black hole accretion disks Sawtooth-like oscillations of black hole accretion disks

Apr 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007iaus..238...37m&link_type=abstract

Black Holes from Stars to Galaxies -- Across the Range of Masses. Edited by V. Karas and G. Matt. Proceedings of IAU Symposium #

Computer Science

2

Scientific paper

Black hole candidates sometimes show high frequency quasi-periodic oscillations (QPOs) whose frequency is about 100Hz when the mass of the black hole is 10 solar mass. High frequency QPOs are accompanied by low frequency QPOs. We studied the excitation mechanism of these QPOs by three-dimensional resistive magnetohydrodynamic (MHD) simulations of optically thin black hole accretion disks. Initial state is a rotating disk threaded by weak toroidal magnetic fields. General relativistic effects are simulated by using the pseudo-Newtonian potential. As the magneto-rotational instability (MRI) grows, the disk matter accretes to the black hole. When the temperature of the disk is not too high, the accreting matter accumulates into a torus formed around 10 Schwarzschild radius. We found that the torus sometimes shows sawtooth-like large amplitude oscillations with frequency 10/(M/10)Hz where M is the mass of the black hole in unit of the solar mass. Sawtooth-like oscillation is triggered by the growth of non-axisymmetric m=1 mode (m is the azimuthal mode number), which deforms the inner torus into a crescent shape. During this stage, magnetic fields inside the torus are amplified until magnetic energy becomes comparable to the thermal energy. Subsequently, magnetic reconnection suddenly releases the accumulated magnetic energy and recovers the circular shape of the torus. A new cycle of the oscillation starts when non-axisymmetric m=1 mode begins to grow inside the torus. We found that when large-amplitude sawtooth-like oscillations appear, high frequency QPOs are excited.

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