|Title||The formation of the first supermassive black holes|
Supermassive black holes (SMBHs) are common in the nuclei of nearby galaxies, and SMBHs as massive as several billion solar masses already existed in the early universe, at redshifts z>6. The earliest SMBHs may have been assembled by the combination of mass accretion onto stellar-mass seed BHs, left behind by the first generation of stars, and by numerous mergers between these growing seeds. Alternatively, SMBHs could be formed directly, by the rapid collapse of gas in rare special environments in the early universe, where the primordial gas can shed its angular momentum and avoid fragmenting into stars. I will review these two competing scenarios, and discuss how they might be distinguished by future observations.