Clumpy Structures within the Turbulent Primordial Cloud
Abstract
The primordial clouds in the mini-halos hatch the first generation stars of the universe, which play a crucial role in cosmic evolution. In this paper, we investigate how the turbulence impacts the structure of primordial star-forming cloud. Previous cosmological simulations of the first star formation predicted a typical mass of around 100 \, M, which conflicts with recent observations of extremely metal-poor stars suggesting a lower mass scale of around 25 \, M. The discrepancy may arise from unresolved turbulence in the star-forming cloud, driven by primordial gas accretion during mini-halo formation in the previous simulation. To quantitatively examine the turbulence effect on the primordial cloud formation, we employ the adaptive mesh refinement code Enzo to model the gas cloud with primordial composition, including artificial-driven turbulence on the cloud scale and relevant gas physics. This artificial-driven turbulence utilizes a stochastic forcing model to mimic the unresolved turbulence inside mini-halos. Our results show that turbulence with high Mach number and compressional mode effectively fragments the cloud into several clumps, each with dense cores of 22.7 - 174.9 \, M that undergo Jeans instability to form stars. Fragmentation caused by intense and compressive turbulence prevents the runaway collapse of the cloud. The self-bound clumps with smaller masses in turbulent primordial cloud suggest a possible pathway to decrease the theoretical mass scale of first stars, further reconciling the mass discrepancy between simulations and observations.