Formation of primordial stars in a ACDM universe

Naoki Yoshida, Kazuyuki Omukai, Lars Hernquist, Tom Abel

Research output: Contribution to journalArticlepeer-review

378 Citations (Scopus)


We study the formation of the first generation of stars in the standard cold dark matter model. We use a very high resolution cosmological hydrodynamic simulation that achieves a dynamic range of ∼1010 in length scale. With accurate treatment of atomic and molecular physics, including the effect of molecular line opacities and cooling by collision-induced continuum emission, it allows us to study the chemothermal evolution of primordial gas clouds to densities up to ρ × 2 × 10-8 g cm -3 (nH ∼ 1016 cm-3) without assuming any a priori equation of state, an improvement of 6 orders of magnitude over previous three-dimensional calculations. We study the evolution of a primordial star-forming gas cloud in the cosmological simulation in detail. The cloud core becomes marginally unstable against chemothermal instability when the gas cooling rate is increased owing to three-body molecule formation. However, since the core is already compact at that point, runaway cooling simply leads to fast condensation to form a single protostellar seed. During the final dynamical collapse, small angular momentum material collapses faster than the rest of the gas and selectively sinks inward. Consequently, the central regions have little specific angular momentum, and rotation does not halt collapse. We, for the first time, obtain an accurate gas mass accretion rate within a 10 M innermost region around the protostar. We carry out protostellar evolution calculations using the obtained accretion rate. The resulting mass of the first star when it reaches the zero-age main sequence is MZAMS ∼ 100 M, and less (≳60 M ) for substantially reduced accretion rates.

Original languageEnglish
Pages (from-to)6-25
Number of pages20
JournalAstrophysical Journal
Issue number1 I
Publication statusPublished - 2006 Nov 20
Externally publishedYes


  • Cosmology: theory
  • Early universe
  • Galaxies: formation
  • Stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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