Bondi-Hoyle-Lyttleton accretion onto ultra dense dark matter halos and direct collapse black holes

TL;DR

This paper proposes a scenario where intermediate-mass black holes form from accretion onto ultra dense dark matter halos shortly after recombination, potentially seeding early supermassive black holes.

Contribution

It introduces a novel formation pathway for intermediate-mass black holes via Bondi-Hoyle-Lyttleton accretion in dense dark matter halos formed from small-scale curvature fluctuations.

Findings

Dense dark matter halos can lead to rapid gas collapse and black hole formation.

Suppression of molecular cooling prevents fragmentation, enabling black hole seed formation.

High-redshift black holes could seed the early growth of supermassive black holes.

Abstract

We suggest a formation scenario of black holes with intermediate mass $\sim 10^3 M_\odot$, by post recombination Bondi-Hoyle-Lyttleton accretion into ultra dense dark matter halos (UDMH) of $\sim 10^5 M_\odot$, which have formed around the recombination epoch. Such UDMH can result from rare curvature fluctuations on small scales whose amplitude is still well below the current Cosmic Microwave Background (CMB) spectral distortion limits. Gas accreted by the UDMH is heated to virial temperatures above which atomic cooling is efficient, cools rapidly to about $\sim 8000$ K and collapses on the free fall time of few $10^4$ yr to the halo core, until supported by rotation. Further fragmentation due to molecular cooling is prevented by the suppression of $H_2$ molecule formation by the CMB photons at redshifts $z> 200-400$. We find that the rotationally supported gas disk will be compact and massive enough to undergo self-gravitational instability in some cases, plausibly where accretion is into a nearly spherical UDMH which has formed from a rare peak in the density field. This results in a further, rapid transfer of mass inwards due to viscous forces and gravitational torques leading to the formation of a supermassive star and/or black hole of about $10^3 M_\odot$ at redshifts of a few hundred. Such intermediate mass black holes formed at high redshifts can have a large-enough abundance to seed the first super massive black holes and help explain the abundance of active galaxies detected now at increasingly larger redshifts by the James Webb Space Telescope.