At https://phys.org/news/2021-01-scientists-black-holes-stupendously-large…. … whilst small to medium size black holes continue to remain invisible cosmologists are now putting forward the idea there are stupendously large black holes lurking out there in space, now known as SLABs in shorthand. These are envisaged to grow much larger than run of the mill 'supermassive' black holes which appear to link in virtually all galaxies. These are thought to reside in the heart of galaxies, in the galactic nuclei – the bulls eye. They enlarge their size by swallowing and gobbling up stars and gases from their surroundings, a lot of which is supposed to exist near the galactic centres. Cosmologists and astrophysicists however also envisage a sort of upper limit that black holes can grow. It should be pointed out here that the existence of black holes is entirely theoretical as they are invisible. They may not exist. It may all be in the heads of cosmologists.
A new study has come up with a way to make supermassive black holes stupendously large, and therefore get around the limits set by earlier scientists on the size of supermassive black holes. Hope you are keeping up on this. The idea being put forwards is that black holes may have formed prior to the formation of galaxies. They would therefore exist independantly of galaxies [but the supermassive variety would remain locked into the hearts of galaxies and restricted in size]. In other words, the stupendous variety did not form from collapsing stars, a major component of black hole theory. Instead, they formed moments after Big Bang, and they are still lurking out there in space. At this point we find the real reason for projecting the idea of stupendous black holes and that is to account for the mysterious and invisible so called dark matter that is thought to exist in intergalactic space. We are told nobody can explain what dark matter consists of so the idea of SLABs is to address that issue. We are then informed the idea goes back to Stephen Hawking, and an associate who is one of the authors of the study, Bernard Carr. They claimed that in the first moments following Big Bang [another hypothesis, a sort of alternative Creation story] fluctuation in the density of emerging space could have resulted in some regions of the universe collapsing into black holes. Put that in your pipe and smoke it.