Fragmentation instability of molecular clouds: Numerical simulations

We simulate fragmentation and gravitational collapse of cold, magnetized mo lecular clouds. We explore the nonlinear development of an instability medi ated by ambipolar diffusion, in which the collapse rate is intermediate to fast gravitational collapse and slow quasistatic collapse. Initially unifor m stable clouds fragment into elongated clumps with masses largely determin ed by the cloud temperature, but substantially larger than the thermal Jean s mass. The clumps are asymmetric, with significant rotation and vorticity, and lose magnetic flux as they collapse. The clump shapes, intermediate co llapse rates, and infall profiles may help explain observations not easily fit by contemporary slow or rapid collapse models.