Ambipolar diffusion in the magnetorotational instability

Matthew Walter Kunz, Steven A. Balbus

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

The effects of ambipolar diffusion on the linear stability of weakly ionized accretion discs are examined. Earlier work on this topic has focused on axial magnetic fields and perturbation wavenumbers. We consider here more general field and wavenumber geometries, and find that qualitatively new results are obtained. Provided a radial wavenumber and azimuthal field are present along with their axial counterparts, ambipolar diffusion will always be destabilizing, with unstable local modes appearing at well-defined wavenumber bands. The wavenumber corresponding to the maximum growth rate need not, in general, lie along the vertical axis. Growth rates become small relative to the local angular velocity when the ion-neutral collision time exceeds the orbital time. In common with Hall electromotive forces, ambipolar diffusion destabilizes both positive and negative angular velocity gradients. In at least some cases, therefore, uniformly rotating molecular cloud cores may reflect the marginally stable state of the ambipolar magnetorotational instability.

Original languageEnglish (US)
Pages (from-to)355-360
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Volume348
Issue number1
DOIs
StatePublished - Feb 11 2004

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Accretion, accretion discs
  • ISM: magnetic fields
  • Instabilities
  • MHD
  • Turbulence

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