SUPERMASSIVE BLACK HOLES. “The existence of supermassive black holes with masses of around 19(9) Mʘ (where Mʘ is the solar mass) only 800 Myr after the Big Bang indicates that there must have been an early intense convergence of mass in ‘rare’ locations, occurring only roughly ten times per co-moving cubic gigaparsec.”
https://www.nature.com/articles/s41586-019-0873-4