Monday, October 07, 2013 at 4:00 PM

JILA Auditorium

Anders Johansen, Lund University

"Simulations of magnetized accretion disks"

Abstract:

My seminar concerns the dynamics of strongly magnetised accretion discs. Discs penetrated by strong azimuthal fields are unstable to the Parker instability. The buoyant magnetic field rises to form big arcs, and the vertical field component of the arcs is in turn unstable to the magnetorotational instability. A turbulent state with efficient angular momentum transport follows. Surprisingly, the azimuthal magnetic field does not escape from the disc, but is replenished as gas parcels stream down towards the mid-plane along inclined field lines. The replenishment of the azimuthal field is caused by the shearing of a spontaneously arising large scale radial field structure. Torques from thelarge-scale magnetic field result in very high accretion rates with no need for high gas column densities that would result in gravitational fragmentation of the disc.

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