Prog. Theor. Phys. Vol. 100 No. 5 (1998) pp. 881-903

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Invited Papers

Thermal and Dynamical Evolution of Primordial Gas Clouds

— On the Formation of First Luminous Objects —

Ryoichi Nishi,^*) Hajime Susa,^*,^**) Hideya Uehara,^**,^***) Masako Yamada^****) and Kazuyuki Omukai^*****)

Department of Physics, Kyoto University, Kyoto 606-8502, Japan
^*Center for Computational Physics, University of Tsukuba
Tsukuba 305-8571, Japan
^**Division of Theoretical Astrophysics, National Astronomical Observatory
Mitaka 181-8588, Japan

(Received September 21, 1998)

Abstract:

We investigate the thermal and dynamical evolution of primordial gas clouds in the universe after decoupling. Comparing the time scale of dynamical evolution with that of fragmentation, we can estimate the typical fragmentation scale. We propose the following scenario of the formation process of first luminous objects consisting of large number stars. First, by pancake collapse of the overdensity regions in the expanding universe or collision between clouds in potential wells, quasi-plane shocks form. If the shock-heated temperature is higher than about 10⁴ K, the post-shock gas cools down to several hundred K by H₂ line cooling, and the shock-compressed layer fragments into filamentary clouds. The filamentary cloud collapses dynamically once more and fragments into cloud cores. Finally, a primordial star forms in a cloud core. We show that the minimum mass of the first star is essentially determined by the Chandrasekhar mass. Also, we investigate the dynamical collapse of cloud cores by numerical simulation and show that the evolution paths of the central regions of the cores depend only very weakly on the total core mass. After mass accretion, a massive star may be formed in a core, since the estimated mass accretion rate is very large. In such a case, it may be possible for many massive stars form almost simultaneously. Then the clouds can be luminous objects. On the other hand, if the shock-heated temperature is lower, effective star formation is delayed significantly.

URL : http://ptp.ipap.jp/link?PTP/100/881/
DOI : 10.1143/PTP.100.881

^*)E-mail: nishi@tap.scphys.kyoto-u.ac.jp
^**)E-mail: susa@rccp.tsukuba.ac.jp
^***)E-mail: uehara@th.nao.ac.jp
^****)E-mail: masako@tap.scphys.kyoto-u.ac.jp
^*****)E-mail: omukai@tap.scphys.kyoto-u.ac.jp

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Citing Article(s) :

Progress of Theoretical Physics Supplement No.147 (2002) pp. 99-127 :
The Dependence of Fragmentation of Metal-Deficient Gas Clouds on H₂ and HD Cooling and the Initial Mass Function of First Generation Stars

Fumitaka Nakamura and Masayuki Umemura

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