[vsnet-chat 7132] Hydrodynamic Perturbations in Accretion Disks

[Taichi Kato]

Hydrodynamic Perturbations in Accretion Disks

   The origin of viscosity in very low quiescence of dwarf novae (or FU Ori-
like stars) has been a serious problem.  Traditional magneto-rotational
instability (=MRI) has generally been considered insufficient or inefficient
(quenched by low electric condution).  This hydrodynamic turbulence would
be a promising alternative.

Paper: astro-ph/0507046
Date: Sat, 2 Jul 2005 01:53:08 GMT   (28kb)

Title: Growth of Hydrodynamic Perturbations in Accretion Disks: Possible Route
  to Non-Magnetic Turbulence
Authors: Banibrata Mukhopadhyay, Niayesh Afshordi, Ramesh Narayan
Comments: 4 pages; to appear in the Proceedings of COSPAR Colloquium "Spectra &
  Timing of Compact X-ray Binaries," January 17-20, 2005, Mumbai, India;
  prepared on the basis of the talk presented by Mukhopadhyay
\\
  We study the possible origin of hydrodynamic turbulence in cold accretion
disks such as those in star-forming systems and quiescent cataclysmic
variables. As these systems are expected to have neutral gas, the turbulent
viscosity is likely to be hydrodynamic in origin, not magnetohydrodynamic.
Therefore MRI will be sluggish or even absent in such disks. Although there are
no exponentially growing eigenmodes in a hydrodynamic disk, because of the
non-normal nature of the eigenmodes, a large transient growth in the energy is
still possible, which may enable the system to switch to a turbulent state. For
a Keplerian disk, we estimate that the energy will grow by a factor of 1000 for
a Reynolds number close to a million.
\\ ( http://arXiv.org/abs/astro-ph/0507046 ,  28kb)