  We present high-angular-resolution observations of the massive star forming
core DR21(OH) at 880 mum using the Submillimeter Array (SMA). The dense core
exhibits an overall velocity gradient in a Keplerian-like pattern, which breaks
at the center of the core where SMA 6 and SMA 7 are located. The dust
polarization shows a complex magnetic field, compatible with a toroidal
configuration. This is in contrast with the large, parsec-scale filament that
surrounds the core, where there is a smooth magnetic field. The total magnetic
field strengths in the filament and in the core are 0.9 and 2.1 mG,
respectively. We found evidence of magnetic field diffusion at the core scales,
far beyond the expected value for ambipolar diffusion. It is possible that the
diffusion arises from fast magnetic reconnection in the presence of turbulence.
The dynamics of the DR 21(OH) core appear to be controlled energetically in
equal parts by the magnetic field, magneto-hydrodynamic (MHD) turbulence and
the angular momentum. The effect of the angular momentum (this is a fast
rotating core) is probably causing the observed toroidal field configuration.
Yet, gravitation overwhelms all the forces, making this a clear supercritical
core with a mass-to-flux ratio of ~6 times the critical value. However,
simulations show that this is not enough for the high level of fragmentation
observed at 1000 AU scales. Thus, rotation and outflow feedback is probably the
main cause of the observed fragmentation.
