Supercritical dusty BH growth in the early Universe
  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.
