The characteristic black hole mass resulting from direct collapse in the early universe

TL;DR

This study uses cosmological simulations to identify the characteristic mass (~10^5 solar masses) of seed black holes formed via direct collapse in the early universe, supporting the feasibility of rapid supermassive black hole formation.

Contribution

It provides the first detailed simulation-based estimate of the seed black hole mass scale from direct collapse, including accretion rate evolution and effects of Lyman Werner flux.

Findings

Black hole seeds of about 10^5 solar masses form under strong Lyman Werner flux.

Accretion rates reach up to 10 solar masses per year after 10^4 years.

The characteristic mass is roughly twice as high in LES compared to ILES simulations.

Abstract

Black holes of a billion solar masses are observed in the infant universe a few hundred million years after the Big Bang. The direct collapse of protogalactic gas clouds in primordial halos with $\rm T_{vir} \geq 10^{4} K$ provides the most promising way to assemble massive black holes. In this study, we aim to determine the characteristic mass scale of seed black holes and the time evolution of the accretion rates resulting from the direct collapse model. We explore the formation of supermassive black holes via cosmological large eddy simulations (LES) by employing sink particles and following their evolution for twenty thousand years after the formation of the first sink. As the resulting protostars were shown to have cool atmospheres in the presence of strong accretion, we assume here that UV feedback is negligible during this calculation. We confirm this result in a comparison run without sinks. Our findings show that black hole seeds with characteristic mass of $\rm 10^{5} M_{\odot}$ are formed in the presence of strong Lyman Werner flux which leads to an isothermal collapse. The characteristic mass is a about two times higher in LES compared to the implicit large eddy simulations (ILES). The accretion rates increase with time and reach a maximum value of 10 $\rm M_{\odot}/yr$ after $\rm 10^{4}$ years. Our results show that the direct collapse model is clearly feasible as it provides the expected mass of the seed black holes.