Excitation of low-frequency QPOs in black-hole accretion flows

Mami Machida, Ryoji Matsumoto

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26 Citations (Scopus)


We present the results of global three-dimensional magneto-hydrodynamic simulations of black-hole accretion flows. We focus on the dependence of the numerical results on the gas temperature supplied from the outer region. General-relativistic effects were taken into account using the pseudo-Newtonian potential. We ignored radiative cooling of the accreting gas. The initial state was a torus threaded by a weak azimuthal magnetic field. We found that the mass-accretion rate and the mass-outflow rate strongly depend on the temperature of the initial torus. The ratio of the average Maxwell stress generated by the magneto-rotational instability (MRI) to the gas pressure, α ≡ (Bω Bφ/4π) / (P), is α ∼ 0.05 in a hot torus and α ∼ 0.01 in a cool torus. In the cool model, a constant angular momentum inner torus is formed around 4-8 rs, where rs is the Schwarzschild radius. This inner torus deforms itself from a circle to a crescent quasi-periodically. During this deformation, the mass-accretion rate, the magnetic energy and the Maxwell stress increase. As the magnetic energy is released, the inner torus returns to a circular shape and starts the next cycle. The power spectral density (PSD) of the time variation of the mass-accretion rate in the cool model has a low-frequency peak around 10 Hz when we assumed a 10M⊙ black hole. The mass outflow rate in the low temperature model also shows quasi-periodic oscillation.

Original languageEnglish
Pages (from-to)613-626
Number of pages14
JournalPublications of the Astronomical Society of Japan
Issue number3
Publication statusPublished - 2008
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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