Forming the first stars in the universe: The fragmentation of primordial gas

In order to constrain the initial mass function of the first generation of stars (Population III), we investigate the fragmentation properties of metal-free gas in the context of a hierarchical model of structure formation. We investigate the evolution of an isolated 3 a peak of mass 2 x 10(6) M. that collapses at z(coll) similar or equal to 30 using smoothed particle hydrodynamics. We fmd that the gas dissipatively settles into a rotationally supported disk that has a very filamentary morphology. The gas in these filaments is Jeans unstable with M-J similar to 10(3) M.. Fragmentation leads to the formation of high-density (n > 10(8) cm(-3)) clumps that subsequently grow in mass by accreting the surrounding gas and by merging with other clumps up to masses of similar to 10(4) M.. This suggests that the very first stars were rather massive. We explore the complex dynamics of the merging and tidal disruption of these clumps by following their evolution over a few dynamical times.