Formation of Primordial Stars in a ΛCDM Universe

We study the formation of the first generation of stars in the standard colddark matter model, using a very high-resolution hydordynamic simulations. Oursimulation achieves a dynamic range of 10^{10} in length scale. With accuratetreatment of atomic and molecular physics, it allows us to study thechemo-thermal evolution of primordial gas clouds to densities up to n =10^{16}/cc without assuming any a priori equation of state; a six orders ofmagnitudes improvement over previous three-dimensional calculations. All therelevant atomic and molecular cooling and heating processes, including coolingby collision-induced continuum emission, are implemented. For calculatingoptically thick H2 cooling at high densities, we use the Sobolev method. Toexamine possible gas fragmentation owing to thermal instability, we computeexplicitly the growth rate of isobaric perturbations. We show that the cloudcore does not fragment in either the low-density or high-density regimes. Wealso show that the core remains stable against gravitational deformation andfragmentation. We obtain an accurate gas mass accretion rate within a 10 Msuninnermost region around the protostar. The protostar is accreting thesurrounding hot gas at a rate of 0.001-0.01 Msun/yr. From these findings weconclude that primordial stars formed in early minihalos are massive. We carryout proto-stellar evolution calculations using the obtained accretion rate. Theresulting mass of the first star is M_ZAMS = 60-100 Msun, with the exact massdependent on the actual accretion rate.Comment: 27 pages, 13 embedded figures. Revised versio