The Race to Build Supermassive Black Holes

TL;DR

This paper evaluates different formation and growth mechanisms for supermassive black holes in the early universe, concluding that mergers alone are insufficient and accretion models are necessary, possibly involving unconventional processes.

Contribution

It provides a comparative analysis of timescales for black hole growth mechanisms, constraining initial formation scenarios based on accretion timescales.

Findings

Mergers alone cannot account for rapid SMBH growth.

Accretion models are essential to explain early SMBH formation.

Unconventional processes may be involved in initial black hole formation.

Abstract

The high redshifts of the most distant known quasars, and the best estimates of their black hole masses, require that supermassive black holes (SMBHs) must have formed very early in history. Several mechanisms for creating and growing these holes have been proposed. Here we present an evaluation of the timescales needed for various critical processes in order to discriminate between the proposed scenarios. We find in particular that mergers alone are not able to grow the black holes at a sufficient rate. Accretion models offer a solution and we use accretion timescales to constrain the manner in which the black hole was first formed. This analysis implies, but does not require, the action of some unconventional process.