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

Abstract

The origin of supermassive black holes (with $\gtrsim 10^9{M}_{\odot }$) in the early universe (redshift $z\sim 7$) 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 (MHD) 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.

arXiv comment13 pages, 10 figures, 1 table; accepted for publication in ApJ

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• Role of magnetic fields in the formation of direct collapse black holes
• Magnetic Effects Promote Supermassive Star Formation in Metal-enriched Atomic-cooling Halos
• Magnetic braking during direct collapse black hole formation
• Effects of chemically homogeneous evolution of the first stars on the 21-cm signal and reionization
• Nitrogen enhancement of GN-z11 by metal pollution from supermassive stars