Supermassive black holes are classically defined as black holes with a mass above 0.1 million to 1 million . Some astronomers have begun labeling black holes of at least 10 billion as ultramassive black holes. Most of these (such as TON 618) are associated with exceptionally energetic quasars. Even larger ones have been dubbed stupendously large black holes (SLAB) with masses greater than 100 billion . Although they noted there is currently no evidence that stupendously large black holes are real, they noted that supermassive black holes almost that size do exist. Some studies have suggested that the maximum mass that a black hole can reach, while being luminous accretors, is of the order of ~50 billion .