This is an ordered list of the most massive black holes so far discovered (and probable candidates), measured in units of solar masses (M☉), approximately 2×1030 kilograms. An artist's impression of a supermassive black hole devouring matter from an accretion disc Introduction: PComparisons of large and small black holes in galaxy OJ 287 to the Solar System. 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. Unambiguous dynamical evidence for SMBHs exists only in a handful of galaxies;[1] these include the Milky Way, the Local Group galaxies M31 and M32, and a few galaxies beyond the Local Group, e.g. NGC 4395. In these galaxies, the mean square (or root mean square) velocities of the stars or gas rises as ~1/r near the center...