Supermassive Star Formation in Magnetized Atomic-cooling Gas Clouds: Enhanced Accretion, Intermittent Fragmentation, and Continuous Mergers

The origin of supermassive black holes (with ≳10 9 M ⊙ ) in the early universe (redshift z ∼ 7) remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We focus on...

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Bibliographic Details
Published in:The Astrophysical journal 2021-08, Vol.917 (1), p.34
Main Authors: Hirano, Shingo, Machida, Masahiro N., Basu, Shantanu
Format: Article
Language:English
Subjects:
Accretion
Angular momentum
Astrophysics
Black holes
Cloud formation
Clouds
Coalescence
Coalescing
Collapse
Cooling
Deposition
Fluid flow
Fragmentation
Fragments
Gravitational collapse
Growth rate
Magnetic effects
Magnetic fields
Magnetohydrodynamic simulation
Magnetohydrodynamical simulations
Massive stars
Momentum transfer
Population III stars
Primordial magnetic fields
Protostars
Red shift
Star & galaxy formation
Star formation
Stars & galaxies
Supermassive black holes
Supermassive stars
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Summary:The origin of supermassive black holes (with ≳10 9 M ⊙ ) in the early universe (redshift z ∼ 7) remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We focus on the magnetic effects on star formation that occurs in an atomic-cooling gas cloud. Using a set of three-dimensional magnetohydrodynamic simulations, we investigate the star formation process in the magnetized atomic-cooling gas cloud with different initial magnetic field strengths. Our simulations show that the primordial magnetic seed field can be quickly amplified during the early accretion phase after the first protostar formation. The strong magnetic field efficiently extracts angular momentum from accreting gas and increases the accretion rate, which results in the high fragmentation rate in the gravitationally unstable disk region. On the other hand, the coalescence rate of fragments is also enhanced by the angular momentum transfer due to the magnetic effects. Almost all the fragments coalesce to the primary star, so the mass growth rate of the massive star increases due to the magnetic effects. We conclude that the magnetic effects support the direct collapse scenario of supermassive star formation.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac0913