Origin of supermassive black holes in massive metal-poor protoclusters

TL;DR

This paper explores how dense, low-metallicity protostar clusters can form supermassive black holes through collisions and gas accretion, offering an alternative to classical direct collapse scenarios, with implications for early universe observations.

Contribution

It introduces a generalized formation mechanism for supermassive black holes in metal-poor protoclusters, considering various initial mass functions and feedback effects.

Findings

Objects of at least 10^4 solar masses can form with inefficient feedback.

Massive objects (~10^3 solar masses) can form when accretion is feedback-limited.

Potential formation of intermediate mass black holes (~10^4 solar masses or more).

Abstract

While large numbers of supermassive black holes have been detected at z>6, their origin is still essentially unclear. Numerical simulations have shown that the conditions for the classical direct collapse scenario are very restrictive and fragmentation is very difficult to be avoided. We thus consider here a more general case of a dense massive protostar cluster at low metallicity (<~ 10^{-3} Z_solar) embedded in gas. We estimate the mass of the central massive object, formed via collisions and gas accretion, considering the extreme cases of a logarithmically flat and a Salpeter-type initial mass function. Objects with masses of at least 10^4 solar could be formed for inefficient radiative feedback, whereas ~10^3 solar mass objects could be formed when the accretion time is limited via feedback. These masses will vary depending on the environment and could be considerably larger, particularly due to the continuous infall of gas into the cloud. As a result, one may form intermediate mass black holes of ~ 10^4 solar masses or more. Upcoming observations with the James Webb Space Telescope (JWST) and other observatories may help to detect such massive black holes and their environment, thereby shedding additional light on such a formation channel.