The Origin of Supermassive Black Holes from Pop III.1 Seeds

TL;DR

This paper reviews a cosmological model where supermassive black holes originate from Pop III.1 star remnants, explaining their initial mass, distribution, and evolution, and compares predictions with recent astronomical observations.

Contribution

It introduces a detailed Pop III.1 seed-based model for SMBH formation, linking dark matter effects and early universe conditions to SMBH properties and distributions.

Findings

SMBH seeds have a characteristic mass of ~10^5 solar masses.

All SMBHs form by redshift z~20 with initially unclustered distribution.

High-redshift SMBHs are predominantly single objects, with binaries forming later.

Abstract

The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. Here we review the features of a cosmological model of SMBH formation from Pop III.1 seeds, i.e., remnants of metal-free stars forming in locally-isolated minihalos, where energy injection from dark matter particle annihilation alters the structure of the protostar allowing growth to supermassive scales (Banik et al. 2019; Singh et al. 2023; Cammelli et al. 2024). The Pop III.1 model explains the paucity of intermediate-mass black holes (IMBHs) via a characteristic SMBH seed mass of $\sim10^5\:M_\odot$ that is set by the baryonic content of minihalos. Ionization feedback from supermassive Pop III.1 stars sets the cosmic number density of SMBHs to be $n_{\rm SMBH}\lesssim 0.2\:{\rm Mpc}^{-3}$. The model then predicts that all SMBHs form by $z\sim20$ with a spatial distribution that is initially unclustered. SMBHs at high redshifts $z\gtrsim7$ should all be single objects, with SMBH binaries and higher order multiples emerging only at lower redshifts. We also discuss the implications of this model for SMBH host galaxy properties, occupation fractions, gravitational wave emission, cosmic reionization, and the nature of dark matter. These predictions are compared to latest observational results, especially from HST, JWST and pulsar timing array observations.