Ultramassive black holes are cosmic titans that surpass even the massive supermassive black holes found at the hearts of large galaxies. One such monster lies at the center of the Phoenix cluster, 5.8 billion light-years away, with an estimated mass of 100 billion times the sun. Another giant ultramassive black hole is located around a billion light-years away, with a mass of approximately 66 billion times the sun.
Researchers believe that these massive black holes are held back by a natural limit due to the way they grow and consume gas and dust from their surroundings. According to Priyamvada Natarajan, a scientist at Yale University who led the study, “supermassive black holes stunt their own growth.” Gas flowing into the galaxy’s center feeds the supermassive black hole, but only a small portion of it is accreted before being blasted away as powerful outflows.
These outflows eventually impact gas farther out from the galaxy, heating and transforming it. This process prevents star formation and pushes gas away from the central region, cutting off the black hole’s food supply and stunting its growth. As a result, there is a natural feedback loop to black hole growth, which sets a limit on their size.
The team estimates that this limit is around 100 billion solar masses for ultramassive black holes. If confirmed, Phoenix A would not only be the most massive black hole detected but also potentially the largest black hole ever discovered.
Source: https://www.space.com/ultramassive-black-holes-how-big