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Magnetohydrodynamic Turbulence in Accretion Disks

Recent work on the structure of magnetic fields in a turbulent medium gives predictions for the properties of the magnetic flux tubes as a function of the Mach number and scale of the turbulence, and the resistivity and viscosity of the fluid. Here I discuss the implications of this work for accretion disks. I show that although accretion disk flux tubes are usually almost completely evacuated, they are nevertheless less buoyant than previous estimates have suggested. I also note that vertical magnetic flux tends to be ejected from the outer edge of accretion disks, so evidence for continued magnetic activity in such systems should be interpreted as supporting the existence of dynamo activity.