Collapse of a Molecular Cloud Core to Stellar Densities: The First Three-dimensional Calculations

We present results from the first three-dimensional calculations ever tofollow the collapse of a molecular cloud core (~ 10^{-18} g cm^{-3}) to stellardensities (> 0.01 g cm^{-3}). The calculations resolve structures over 7 ordersof magnitude in spatial extent (~ 5000 AU - 0.1 R_\odot), and over 17 orders ofmagnitude in density contrast. With these calculations, we consider whetherfragmentation to form a close binary stellar system can occur during the secondcollapse phase. We find that, if the quasistatic core that forms before thesecond collapse phase is dynamically unstable to the growth of non-axisymmetricperturbations, the angular momentum extracted from the central regions of thecore, via gravitational torques, is sufficient to prevent fragmentation and theformation of a close binary during the subsequent second collapse.