Hypermassive black hole

Hypermassive black holes (or HMBH) were the largest black holes in the universe. Unlike common supermassive black holes making up the centres of galaxies (which ranged from less than a million to over a billion times the mass of a yellow dwarf star) these hypermassive black holes could range up to 16 billion times the mass of a common yellow star, thousands of times heavier than the Galactic center. These black holes were so large that they could swallow up entire galaxies. Sometimes, these black holes formed the centres of galaxy clusters, with hundreds of galaxies in orbit around them.

Formation and mass
HMBH's were formed in the same way as other black holes above stellar mass (Such as IMBH and SMBH) but on a much larger scale. They were formed in multiple galaxy mergers, when many thousands of Supermassive black holes merged.

These mergers often blew entire galaxies apart, and scattered millions of star systems across the universe. Some cosmologists believed that the creation of HMBH's was responsible for wondering star systems like Sebbadon, as well as solitary Supermassive black holes.

Hypermassive black holes were large enough to pull almost anything into their grip. They had event horizons spanning thousands of light years.

Some scientists believe that these black holes will eventually cause the death of the universe, becoming to massive they pull the entire fabric of space inside themselves, as well as everything else in the universe.