Role of primordial black holes in the direct collapse scenario of supermassive black hole formation at high redshifts

TL;DR

This paper investigates how primordial black holes could heat collapsing gas in the early universe, potentially enabling the formation of supermassive black holes by preventing molecular hydrogen cooling at high redshifts.

Contribution

It demonstrates that primordial black holes of mass greater than 0.01 solar masses can inhibit H2 formation, maintaining high temperatures necessary for direct collapse black hole formation.

Findings

Primordial black holes can heat gas to 10^4 K, preventing H2 cooling.

Gas remains at high temperature until reaching critical density, facilitating direct collapse.

The mechanism supports formation pathways for supermassive black holes at high redshifts.

Abstract

In this paper, we explore the possibility of accreting primordial black holes as the source of heating for the collapsing gas in the context of the direct collapse black hole scenario for the formation of super-massive black holes (SMBHs) at high redshifts, $z\sim 6-7$. One of the essential requirements for the direct collapse model to work is to maintain the temperature of the in falling gas at $\approx 10^4$ K. We show that even under the existing abundance limits, the primordial black holes of masses $\gtrsim 10^{-2} \ {\rm M}_\odot$, can heat the collapsing gas to an extent that the ${\rm H}_2$ formation is inhibited. The collapsing gas can maintain its temperature at $10^4$ K till the gas reaches a critical density $n_{crit} \approx 10^3$ cm$^{-3}$, at which the roto-vibrational states of ${\rm H}_2$ approaches local thermodynamic equilibrium and ${\rm H}_2$ cooling becomes inefficient. In the absence of ${\rm H}_2$ cooling the temperature of the collapsing gas stays at $\approx 10^4$ K even as it collapses further. We discuss scenarios of subsequent angular momentum removal and the route to find collapse through either a supermassive star or a supermassive disk.