Formation of Massive Primordial Stars in a Reionized Gas
Formation of Massive Primordial Stars in a Reionized Gas
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DOI：
10.1086/522202
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发表时间：
2007-06
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影响因子：
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通讯作者：
Naoki Yoshida;K. Omukai;L. Hernquist
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文献类型：
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作者：
Naoki Yoshida;K. Omukai;L. Hernquist
我们使用具有前所未有的分辨率的宇宙流体动力学模拟来研究高红移电离气体中原始恒星的形成。我们的方法包括所有相关的原子和分子物理学，以跟踪星际气体云的热演化到 ~1018 cm-3 的极高密度。我们在宇宙学模拟中将恒星形成气体云定位在再电离区域内。通过 HD 线冷却，气体云冷却至几十开尔文，这比仅通过氢气冷却所能达到的温度要低。由于温度较低，当气体云的质量约为 40 M☉ 时，会触发第一次失控塌缩。我们表明，云核在整个演化过程中保持稳定，免受化学热不稳定和重力变形的影响。因此，形成了单个原恒星种子，它以 ≳ 10-3 M☉ yr-1 的速率吸积周围的热气体。我们使用推断的吸积率进行原恒星演化计算。当恒星到达零年龄主序带时，恒星的最终质量为 MZAMS ~ 40 M☉。由于获得的 MZAMS 与塌缩母云的质量一样大，因此最终的恒星质量可能接近该值。如此巨大而不是异常巨大的原始恒星预计将通过爆炸形成黑洞的超新星/超新星来引起宇宙的早期化学富集，并且也可能是高红移γ射线爆发的前身。最近发现的超贫金属恒星的元素丰度模式表明，它们可能诞生于星际介质中，而这些星际介质中的大质量原始恒星的超新星富含金属。
We use cosmological hydrodynamic simulations with unprecedented resolution to study the formation of primordial stars in an ionized gas at high redshifts. Our approach includes all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high densities of ~1018 cm-3. We locate a star-forming gas cloud within a reionized region in our cosmological simulation. The gas cloud cools down to a few tens of kelvins by HD line cooling, and this is lower than possible by H2 cooling only. Owing to the low temperature, the first runaway collapse is triggered when the gas cloud's mass is ~40 M☉. We show that the cloud core remains stable against chemothermal instability and also against gravitational deformation throughout its evolution. Consequently, a single protostellar seed is formed, which accretes the surrounding hot gas at the rate ≳ 10-3 M☉ yr-1. We carry out protostellar evolution calculations using the inferred accretion rate. The resulting mass of the star when it reaches the zero-age main sequence is MZAMS ~ 40 M☉. Since the obtained MZAMS is as large as the mass of the collapsing parent cloud, the final stellar mass is likely close to this value. Such massive, rather than exceptionally massive, primordial stars are expected to cause early chemical enrichment of the universe by exploding as black hole-forming super/hypernovae and may also be progenitors of high-redshift γ-ray bursts. The elemental abundance patterns of recently discovered hyper-metal-poor stars suggest that they might have been born from the interstellar medium that was metal-enriched by the supernovae of these massive primordial stars.