An over-massive black hole in the compact lenticular galaxy NGC 1277

Observations of the stellar dynamics of the compact lenticular galaxy NGC 1277 show that its central black hole accounts for more than half of the mass of the host galaxy’s bulge, indicating that lenticular galaxies do not follow the usual black-hole mass scaling relations. A galaxy dominated by an over-massive black hole It's thought that all massive galaxies have a supermassive black hole at their centre, typically accounting for about 0.1% of the stellar-bulge mass of the galaxy. Until now, the small galaxy NGC 4486B has held the distinction of having the largest published fraction of it mass in a black hole, at 11%. This paper reports something on a much larger scale — an over-massive black hole of 17 billion solar masses that makes up 59% of the bulge mass of the compact lenticular galaxy NGC 1277. Five other compact galaxies have properties similar to those of NGC 1277, and these may also contain over-sized black holes. Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes are believed to correlate with properties of the host-galaxy bulge component 1 . Several explanations have been proposed for the existence of these locally established empirical relationships, including the non-causal, statistical process of galaxy–galaxy merging 2 , direct feedback between the black hole and its host galaxy 3 , and galaxy–galaxy merging and the subsequent violent relaxation and dissipation 4 . The empirical scaling relations are therefore important for distinguishing between various theoretical models of galaxy evolution 5 , 6 , and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy 7 , 8 . Until now, the galaxy with the largest known fraction of its mass in its central black hole (11 per cent) was the small galaxy NGC 4486B 1 , 9 . Here we report observations of the stellar kinematics of NGC 1277, which is a compact, lenticular galaxy with a mass of 1.2 × 10 11 solar masses. From the data, we determine that the mass of the central black hole is 1.7 × 10 10 solar masses, or 59 per cent of its bulge mass. We also show observations of five other compact galaxies that have properties similar to NGC 1277 and therefore may also contain over-massive black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated g