Formation of Host Clouds of First Stars in the Early Universe

概要

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It is widely accepted that various structures of the universe are formed through the gravitational instability of the density perturbations imprinted by the quantum fluctuations. First stars are also formed as a consequence of the evolved density perturbations. However, they are not formed from the stellar size perturbations such as M 〜 1 - 10^2M_〓. Recent theoretical investigations suggest the first stars are formed in more massive "parent" clouds, with M≥10^6M_〓. The key physics of the formation of such small hosts is the formation of hydrogen molecules in them. Since the virial temperature of such clouds are less than 10^4K, they are not cooled by atomic cooling processes. Therefore, hydrogen molecules are requiredas the main coolant of primordial gas at 10^4K, because (heir rotation/vibration levels are excited even at such low temperature. In this chapter, gravitational collapse of density perturbations in Cold Dark Matter (CDM) universe is reviewed. Second, the formation processes of hydrogen molecules and the cooling mechanisms in primordial gas are summarized. Finally, the condition of the formation of cold dense gas clouds that host the first stars is shown.
理論物理学刊行会の論文
2003-02-28