Collapse of a molecular cloud core to stellar densities: The first three-dimensional calculations

We present results from the first three-dimensional calculations ever to fo llow the collapse of a molecular cloud core (similar to 10(-18) g cm(-3)) t o stellar densities (>0.01 g cm(-3)). The calculations resolve structures o ver 7 orders of magnitude in spatial extent (similar to 5000 AU - 0.1 R.) a nd over 17 orders of magnitude in density contrast. With these calculations , we consider whether fragmentation to form a close binary stellar system c an occur during the second collapse phase. We find that, if the quasi-stati c core that forms before the second collapse phase is dynamically unstable to the growth of nonaxisymmetric perturbations, the angular momentum extrac ted from the central regions of the core, via gravitational torques, is suf ficient to prevent fragmentation and the formation of a close binary during the subsequent second collapse.