Does Dissipation in AGN Disks Couple to the Total Pressure?
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Recent work on the transport of angular momentum in accretion disks suggests
that the Velikhov-Chandrasekhar instability, in which a large scale magnetic
field generates small scale eddys in a shearing environment, may be ultimately
responsible for this process. Although there is considerable controversy about
the origin and maintenance of this field in accretion disks, it turns out that
it is possible to argue, quite generally, using scaling arguments, that this
process is sensitive to the total pressure in an AGN disk, rather than the
pressure contributed by gas alone. We conclude that the resolution of the
conceptual difficulties implied by the presence of strong thermal and viscous
instabilities in radiation pressure and electron scattering dominated does not
lie in models that couple the total dissipation rate to the gas pressure alone,
or to some weighted mean of the gas and radiation pressures.