2024/05/16 by Mana Ito, Ito, Mana, Kazuyuki Omukai +1 · 3 citations
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2405.10073
openalex publication_date 2024/05/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
First stars play crucial roles in development of the universe, influencing events like cosmic reionization and the chemical enrichment. While first stars are conventionally thought to form at around z ∼ 20-30 in the standard Λ Cold Dark Matter (ΛCDM) cosmology, observational constraints on small-scale density fluctuations remain limited, possibly differing significantly from the scale-invariant fluctuations assumed in the ΛCDM model. Should this be the case, the formation of first stars could occur much earlier than typically predicted. In this study, we investigate the formation process of first stars in the extremely early epochs of z \gtrsim 100 in the post-recombination universe. At such early times, the effects of the warm cosmic microwave background (CMB) become significant. We calculate the collapse of primordial star-forming clouds using a one-zone thermo-chemical model that accounts for CMB influences on radiative heating, Compton cooling, and photodissociation reactions. We found that the impact of the CMB on the evolution is limited at z \lesssim 100, with the temperature evolution closely resembling the conventional model. However, within the range 100 \lesssim z \lesssim 400, the formation of H2 via the H- channel is impeded by H- photodetachment induced by the CMB, leading to higher temperatures compared to standard one. Consequently, first stars with masses exceeding 1000 ~M_\odot can emerge at z \gtrsim 100. Furthermore, at z \gtrsim 500, the temperature evolution becomes nearly isothermal solely due to atomic cooling, as H2 formation is entirely suppressed. In such cases, supermassive stars with masses around ∼ 105 ~M_\odot are expected to form solely via atomic cooling. These findings emphasize the significant variation in the typical mass of the first stars depending on the epoch of formation.