We apply a new model for the structure of a magnetic field embedded in a turbulent plasma to stars and accretion disks. This model is based on the popular notion that the magnetic field tends to separate into individual flux tubes. Realistic stellar plasmas are expected to either be in the ideal fluid limit where specific values of resistivity and viscosity can be ignored (e.g., the top of the solar convection zone) or the resistive limit (the bulk of the solar convection zone). In contrast, hot accretion disks are usually in the ideal fluid limit. We find that with the exception of radiation pressure-dominated environments, flux tubes are no more, and perhaps slightly less, buoyant than a diffuse field of comparable energy density. However, in radiation pressure-dominated accretion disks the increased buoyancy of the magnetic field leads to the conclusion that the viscosity associated with magnetic stresses scales with the gas pressure, rather than the total pressure. Finally, if we assume that a stellar magnetic field is limited by the value that would seriously affect the bottom layer of the convection zone, then we can show that the large-scale poloidal field of the Sun cannot be more than a few gauss.
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Ethan T. Vishniac (1995) studied this question.