Ionization degree and magnetic diffusivity in the primordial star-forming clouds

Daisuke Nakauchi, Kazuyuki Omukai, Hajime Susa

研究成果: Article査読

4 被引用数 (Scopus)

抄録

Magnetic fields play such roles in star formation as the angular momentum transport in star-forming clouds, thereby controlling circumstellar disc formation and even binary star formation efficiency. The coupling between the magnetic field and gas is determined by the ionization degree in the gas. Here, we calculate the thermal and chemical evolution of the primordial gas by solving chemical reaction network where all the reactions are reversed. We find that at ∼1014–1018 cm−3, the ionization degree becomes 100–1000 times higher than the previous results due to the lithium ionization by thermal photons trapped in the cloud, which has been omitted so far. We construct the minimal chemical network which can reproduce correctly the ionization degree as well as the thermal evolution by extracting 36 reactions among 13 species. Using the obtained ionization degree, we evaluate the magnetic field diffusivity. We find that the field dissipation can be neglected for global fields coherent over ≳ a tenth of the cloud size as long as the field is not so strong as to prohibit the collapse. With magnetic fields strong enough for ambipolar diffusion heating to be significant, the magnetic pressure effects to slow down the collapse and to reduce the compressional heating become more important, and the temperature actually becomes lower than in the no-field case.

本文言語English
ページ(範囲)1846-1862
ページ数17
ジャーナルMonthly Notices of the Royal Astronomical Society
488
2
DOI
出版ステータスPublished - 2019 9 11

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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