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Dynamo-generated Turbulence and Large-Scale Magnetic Fields in a Keplerian Shear Flow
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The study simulates the nonlinear evolution of magnetized Keplerian shear flows in a local, three‑dimensional, compressible and stratified model. Supersonic flows arise from the Balbus–Hawley magnetic shear instability, and the model imposes vertical fields at the top and bottom boundaries to allow unconstrained horizontal magnetic flux. The simulations show that the system behaves as a dynamo, producing turbulent magnetic fields that dominate kinetic energy by a factor of 3–10, generating a large‑scale toroidal field of even parity that reverses on ~30 orbits, and yielding an effective α viscosity of 0.001–0.005 with Maxwell stresses 3–7 times larger than Reynolds stresses. Published in The Astrophysical Journal (June 1995, DOI 10.1086/175831).
view Abstract Citations (724) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dynamo-generated Turbulence and Large-Scale Magnetic Fields in a Keplerian Shear Flow Brandenburg, Axel ; Nordlund, Ake ; Stein, Robert F. ; Torkelsson, Ulf Abstract The nonlinear evolution of magnetized Keplerian shear flows is simulated in a local, three-dimensional model, including the effects of compressibility and stratification. Supersonic flows are initially generated by the Balbus-Hawley magnetic shear instability. The resulting flows regenerate a turbulent magnetic field which, in turn, reinforces the turbulence. Thus, the system acts like a dynamo that generates its own turbulence. However, unlike usual dynamos, the magnetic energy exceeds the kinetic energy of the turbulence by a factor of 3-10. By assuming the field to be vertical on the outer (upper and lower) surfaces we do not constrain the horizontal magnetic flux. Indeed, a large-scale toroidal magnetic field is generated, mostly in the form of toroidal flux tubes with lengths comparable to the toroidal extent of the box. This large-scale field is mainly of even (i.e., quadrupolar) parity with respect to the midplane and changes direction on a timescale of ∼30 orbits, in a possibly cyclic manner. The effective Shakura-Sunyaev alpha viscosity parameter is between 0.001 and 0.005, and the contribution from the Maxwell stress is ∼3-7 times larger than the contribution from the Reynolds stress. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175831 Bibcode: 1995ApJ...446..741B Keywords: ACCRETION; ACCRETION DISKS; MAGNETOHYDRODYNAMICS: MHD; SHOCK WAVES; TURBULENCE full text sources ADS |