Fragmentation of Molecular Clouds: The Initial Phase of a Stellar Cluster

The isothermal gravitational collapse and fragmentation of a region within a molecular cloud and the subsequent formation of a protostellar cluster are investigated numerically. The clump mass spectrum that forms during the fragmentation phase can be well approximated by a power-law distribution dN/dM~M^-1.5. In contrast, the mass spectrum of protostellar cores that form in the centers of Jeans-unstable clumps and that evolve through accretion and N-body interactions is described by a lognormal distribution with a width that is in excellent agreement with observations of multiple stellar systems.