Role of magnetic fields in the formation of direct collapse black holes

TL;DR

This study uses long-term 3D MHD simulations to show that magnetic fields rapidly amplify during direct collapse black hole formation, stabilizing disks, reducing fragmentation, and influencing the mass and multiplicity of supermassive stars.

Contribution

First long-duration 3D MHD simulations demonstrating magnetic fields' role in stabilizing accretion disks and reducing fragmentation during DCBH formation.

Findings

Magnetic fields are rapidly amplified and reach saturation.

Magnetic fields stabilize disks and reduce fragmentation.

Central clump masses are around 10^5 solar masses with similar accretion rates.

Abstract

Direct collapse black holes (DCBHs) are the leading candidates for the origin of the first supermassive black holes. However, the role of magnetic fields during their formation is still unclear as none of the previous studies has been evolved long enough to assess their impact during the accretion phase. Here, we report the results from a suite of 3D cosmological magneto-hydrodynamic (MHD) simulations which are evolved for 1.6 Myrs comparable to the expected lifetime of supermassive stars (SMSs). Our findings suggest that magnetic fields are rapidly amplified by strong accretion shocks irrespective of the initial magnetic field strength and reach the saturation state. They stabilize the accretion disks and significantly reduce fragmentation by enhancing the Jeans mass in comparison with pure hydrodynamical runs. Although the initial clump masses are larger in MHD runs, the rapid coalescence of clumps in non-MHD cases due to the higher degree of fragmentation results in similar masses. Overall, the central clumps have masses of $\rm 10^5~M_{\odot}$ and the mean mass accretion rates of $\rm \sim 0.1 ~M_{\odot}/yr$ are similar in both MHD and non-MHD cases. The multiplicity of SMSs is significantly reduced in MHD simulations. Such strongly amplified magnetic fields are expected to launch Jets and outflows which may be detected with upcoming radio telescopes.