2018/02/20 by Shingo Hirano, Volker Bromm · 1 citation
Physics and Astronomy · #Accretion (finance) #Angular momentum #Angular velocity #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Differential rotation #Dynamo #Dynamo theory #Magnetic field #Magnetohydrodynamics #Mechanics #Physics #Protostar #RADIUS #Rotation (mathematics) #Rotation period #Star formation #Stars #Stellar rotation #Stellar, planetary, and galactic studies #Turbulence #astro-ph.GA
paper · pdf · doi:10.1093/mnras/sty487
10 pages, 7 figures, accepted to MNRAS
arxiv created 2018/02/20 · openalex publication_date 2018/02/22 · arxiv updated 2018/03/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc. Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfv|\acute\rm e|n radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one. The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without magnetic fields. Considering a physically motivated model for small-scale turbulent dynamo amplification, we find that stellar rotation speed quickly declines if a large fraction of the initial turbulent energy is converted to magnetic energy (≳ 0.14). Alternatively, if the dynamo process were inefficient, for amplification due to flux freezing, stars would become slow rotators if the pre-galactic magnetic field strength is above a critical value, ≃10−8.2 G, evaluated at a scale of nH = 1 cm−3, which is significantly higher than plausible cosmological seed values (∼10−15 G). Because of the rapid decline of the stellar rotational speed over a narrow range in model parameters, the first stars encounter a bimodal fate: rapid rotation at almost the breakup level, or the near absence of any rotation.