If these black holes were just sitting there growing from feeding on material around them, there's no way, when the Universe was less than 10 percent of its current age, they would have had enough time to get that big.
"We found that one possible formation channel for ultra-massive black holes is from the extreme merger of massive galaxies that are most likely to happen in the epoch of the 'cosmic noon',"A slow growth by accretion is just one way in which black holes can gain mass. Another way, which we have actually observed in recent years, is the.
A supercomputer is required, because you need a large volume of space to observe extreme outliers, like ultramassive black holes, and that, in turn, requires a large amount of computing power. But it paid off: by around 10 billion years ago, the researchers saw black holes of around 10 billion solar masses forming.