Supercritical dusty BH growth in the early Universe

TL;DR

This paper investigates how dust in the early Universe could enable supercritical accretion onto black holes, facilitating rapid growth of supermassive black holes observed within the first billion years.

Contribution

It generalizes photon trapping to dusty gas, identifying conditions that promote dust photon trapping and its role in early black hole growth.

Findings

Dust photon trapping is more likely with larger black holes, denser gas, and lower temperatures.

Dust photon trapping can obscure AGNs and enable rapid black hole growth.

Conditions for dust photon trapping are physically plausible in early Universe environments.

Abstract

Supermassive black holes (with $\mathrm{M_{BH} \sim 10^9 M_{\odot}}$) are observed in the first Gyr of the Universe, and their host galaxies are found to contain unexpectedly large amounts of dust and metals. In light of the two empirical facts, we explore the possibility of supercritical accretion and early black hole growth occurring in dusty environments. We generalise the concept of photon trapping to the case of dusty gas and analyse the physical conditions leading to dust photon trapping. Considering the parameter space dependence, we obtain that the dust photon trapping regime can be more easily realised for larger black hole masses, higher ambient gas densities, and lower gas temperatures. The trapping of photons within the accretion flow implies obscured active galactic nuclei (AGNs), while it may allow a rapid black hole mass build-up at early times. We discuss the potential role of such dust photon trapping in the supercritical growth of massive black holes in the early Universe.