Non-axisymmetric Evolution of Dynamically Contracting Disks and Formation of Binary Stars

Using two-dimensional hydrodynamical simulations, we followed the evolution of a dynamically-collapsing, rotating disk permeated by vertical magnetic eld. As a model of a disk, the similarity solution for isothermal, rotating, and magnetized disks are adopted. The disk deforms into a bar during its contraction. In the early stage, the deformation of the disk grows in proportion to (t 0 t) 0:6 , where t 0 denotes the time at which the central density becomes in nitely large. The bar is expected to fragment into many cores, which may evolve into binary or multiple stars after merging.