
A supermassive black hole (SMBH) is an extremely large black hole, on the order of hundreds of thousands to billions of solar masses (M☉), and is theorized to exist in the center of almost all massive galaxies. In some galaxies, there are even binary systems of supermassive black holes, see the OJ 287 system.. . This is an ordered list of the most massive black holes so far discovered (and probable candidates), measured in units of (), approximately 2×10 kilograms. . Due to the very large numbers involved, the listed black holes have their mass values in scientific notation (numbers multiplied to powers of 10). Values with uncertainties are written in. . • • • • •