Dark Matter Accretion into Supermassive Black Holes

TL;DR

This paper revisits the relativistic dark matter accretion rate onto black holes, finding it can be significantly higher than classical estimates, but dark matter contributes minimally to black hole growth compared to baryonic matter.

Contribution

It introduces a relativistic accretion model assuming constant phase space density, showing higher accretion rates and minimal dark matter contribution to black hole mass growth.

Findings

Relativistic accretion rate can be up to five times higher than classical estimates.

Dark matter contributes less than 10% to black hole mass accretion.

Critical flow points are located at 30-150 times the horizon radius.

Abstract

The relativistic accretion rate of dark matter by a black hole is revisited. Under the assumption that the phase space density indicator, $Q=\rho_{\infty}/\sigma^3_{\infty}$, remains constant during the inflow, the derived accretion rate can be higher up to five orders of magnitude than the classical accretion formula, valid for non-relativistic and non-interacting particles, when typical dark halo conditions are considered. For these typical conditions, the critical point of the flow is located at distances of about 30-150 times the horizon radius. Application of our results to black hole seeds hosted by halos issued from cosmological simulations indicate that dark matter contributes to no more than ~10% of the total accreted mass, confirming that the bolometric quasar luminosity is related to the baryonic accretion history of the black hole.