Direct Formation of Supermassive Black Holes via Multi-Scale Gas Inflows in Galaxy Mergers

TL;DR

This paper demonstrates through simulations that galaxy mergers can rapidly funnel gas to form supermassive black holes via direct collapse, explaining their early appearance in the universe.

Contribution

It introduces a new model showing that galaxy mergers naturally produce conditions for direct black hole formation without needing to suppress star formation.

Findings

Merger-driven gas inflows create massive nuclear disks.

A sub-parsec scale gas cloud collapses into a black hole within 100,000 years.

Black holes can grow to billion-solar-mass within a billion years.

Abstract

Observations of distant bright quasars suggest that billion solar mass supermassive black holes (SMBHs) were already in place less than a billion years after the Big Bang. Models in which light black hole seeds form by the collapse of primordial metal-free stars cannot explain their rapid appearance due to inefficient gas accretion. Alternatively, these black holes may form by direct collapse of gas at the center of protogalaxies. However, this requires metal-free gas that does not cool efficiently and thus is not turned into stars, in contrast with the rapid metal enrichment of protogalaxies. Here we use a numerical simulation to show that mergers between massive protogalaxies naturally produce the required central gas accumulation with no need to suppress star formation. Merger-driven gas inflows produce an unstable, massive nuclear gas disk. Within the disk a second gas inflow accumulates more than 100 million solar masses of gas in a sub-parsec scale cloud in one hundred thousand years. The cloud undergoes gravitational collapse, which eventually leads to the formation of a massive black hole. The black hole can grow to a billion solar masses in less than a billion years by accreting gas from the surrounding disk.