WARP STABILITY OF MAGNETICALLY SUPPORTED DISKS

Cold, magnetically supported, self-gravitating disks are evolutionary precursors of protostars. Magnetic tension balances self-gravity in th ese systems, so the magnetic field lines kink as they cross the disk. Previously, we have shown that such disks are marginally stable to in- plane perturbations. Here, we show that a sufficient condition for sta bility of such disks to out-of-plane, warping or tilting, perturbation s is that the azimuthal current in the disk have one polarity as a fun ction of radius. This corresponds to the gravitational acceleration in the disk pointing radially inward for all radii. This criterion is no t necessary, however, and can be violated as long as the vertical magn etic field exceeds the radial magnetic field (in magnitude) everywhere in the disk.