Direct formation of supermassive black holes via multi-scale gas inflows in galaxy mergers

Observations of distant quasars indicate that supermassive black holes of billions of solar masses already existed less than a billion years after the Big Bang(1). Models in which the 'seeds' of such black holes form by the collapse of primordial metal-free stars(2,3) cannot explain the rapid appearance of these supermassive black holes because gas accretion is not sufficiently efficient(4-6). Alternatively, these black holes may form by direct collapse of gas within isolated protogalaxies(7,8), but current models require idealized conditions, such as metal-free gas, to prevent cooling and star formation from consuming the gas reservoir(9-11). Here we report simulations showing that mergers between massive protogalaxies naturally produce the conditions for direct collapse into a supermassive black hole with no need to suppress cooling and star formation. Merger-driven gas inflows give rise to an unstable, massive nuclear gas disk of a few billion solar masses, which funnels more than 10(8) solar masses of gas to a sub-parsec-scale gas cloud in only 100,000 years. The cloud undergoes gravitational collapse, which eventually leads to the formation of a massive black hole. The black hole can subsequently grow to a billion solar masses on timescales of about 10(8) years by accreting gas from the surrounding disk.