Cosmological DCBH formation sites hostile for their growth

TL;DR

This study uses cosmological radiation-hydrodynamics simulations to show that direct collapse black holes in early universe environments experience slow growth due to radiative feedback and high velocities, hindering their development into supermassive black holes.

Contribution

It provides new insights into the long-term accretion behavior of DCBHs, highlighting the impact of their high velocities and environmental factors on their growth potential.

Findings

Accretion rates are far below the Eddington limit due to radiative feedback.

DCBHs often have high velocities (~100 km/s) that reduce accretion.

Formation in metal-poor environments near galactic centers favors rapid growth.

Abstract

The direct collapse (DC) is a promising mechanism that provides massive seed black holes (BHs) with $\sim 10^{5}~M_{\odot}$ in the early universe. To study a long-term accretion growth of a DCBH thus formed, we perform cosmological radiation-hydrodynamics simulations, extending our previous work where we investigated its formation stage. With a high spatial resolution down below the Bondi radius, we show that the accretion rate onto the BH is far below the Eddington value. Such slow mass growth is partly because of the strong radiative feedback from the accreting BH. Moreover, we find that the BH has a large velocity of $\sim 100~{\rm km~s^{-1}}$ relative to the gas after it falls into the first galaxy, which substantially reduces the accretion rate. The latter effect stems from the fact that the DCBHs form in metal-free environments typically at $\sim 1~$kpc from the galaxy. The BH accelerates as it approaches the galactic center due to the gravity. The relative velocity never damps after that, and the BH does not settle down to the galactic center but continues to wander around it. An analytic estimate predicts that the DCBH formation within $\sim 100$~pc around the galactic center is necessary to decelerate the BH with dynamical friction before $z=7$. Since metal enrichment with $Z \sim 10^{-5} - 10^{-3}~Z_\odot$ is expected in such a case, the formation of DCBHs in the metal-poor environments is preferable for the subsequent rapid growth.