skip to main content

SciTech ConnectSciTech Connect

Title: Convection causes enhanced magnetic turbulence in accretion disks in outburst

We present the results of local, vertically stratified, radiation magnetohydrodynamic (MHD) shearing box simulations of magneto-rotational instability (MRI) turbulence appropriate for the hydrogen ionizing regime of dwarf nova and soft X-ray transient outbursts. We incorporate the frequency-integrated opacities and equation of state for this regime, but neglect non-ideal MHD effects and surface irradiation, and do not impose net vertical magnetic flux. We find two stable thermal equilibrium tracks in the effective temperature versus surface mass density plane, in qualitative agreement with the S-curve picture of the standard disk instability model. We find that the large opacity at temperatures near 10{sup 4} K, a corollary of the hydrogen ionization transition, triggers strong, intermittent thermal convection on the upper stable branch. This convection strengthens the magnetic turbulent dynamo and greatly enhances the time-averaged value of the stress to thermal pressure ratio α, possibly by generating vertical magnetic field that may seed the axisymmetric MRI, and by increasing cooling so that the pressure does not rise in proportion to the turbulent dissipation. These enhanced stress to pressure ratios may alleviate the order of magnitude discrepancy between the α-values observationally inferred in the outburst state and those that have been measured from previous localmore » numerical simulations of magnetorotational turbulence that lack net vertical magnetic flux.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4]
  1. Department of Mathematical Science and Advanced Technology, JAMSTEC, Yokohama, Kanagawa 236-0001 (Japan)
  2. Department of Physics, University of California, Santa Barbara, CA 93106 (United States)
  3. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
  4. Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan)
Publication Date:
OSTI Identifier:
22356888
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; AXIAL SYMMETRY; COMPUTERIZED SIMULATION; DENSITY; EQUATIONS OF STATE; INSTABILITY; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; NMR IMAGING; NOVAE; OPACITY; RADIANT HEAT TRANSFER; SOFT X RADIATION; STRESSES; SURFACES; THERMAL EQUILIBRIUM; TRANSIENTS; TURBULENCE