Physics Colloquium
Friday, September 10th, 2004, 4:00 P.M.

Dan Lathrop

Department of Physics, University of Maryland

Liquid sodium flows showing the magneto-rotational instability

Diverse astrophysical phenomena involve the close interplay of rotation and magnetic fields. There is theoretical and computational evidence for the importance of small magnetic fields in destabilizing differential rotation: a process now often called the magneto-rotational instability. This phenomena is invoked to explain how rotating clouds proceed to collapse in star formation. The instability leads to radial outflow of angular momentum, so that matter may fall inward instead of continuing to orbit. Magnetic fields in differentially rotating stars and planetary interiors are also thought to be affected. This colloquium will describe the first direct observation of this instability. The experimental device consists of liquid sodium confined between boundaries defined by a rotating inner sphere and a stationary outer sphere, with an imposed coaxial magnetic field. We characterize an array of observed patterns and dynamics in a saturated magneto-rotational state and relate these observations to theoretical expectations.