«We know that the formation of these supermassive black holes has to be very rapid because we can see very bright quasars very soon after the Big Bang, not much later than the epoch of the first star formation.» (discovermagazine.com)
It also seems to be a key time for the growth of black holes, because we see at that time a peak in the number of bright quasars where these growing black holes reside. (kavlifoundation.org)
The first stars lit up a few - hundred - million - years - long «Dark Age» with spectacular intensity, leading to the rapid creation of heavy elements and black holes that coalesced to form bright quasars (more). (members.nova.org)