A fundamental relation between supermassive black holes and their host galaxies

The masses of supermassive black holes correlate almost perfectly with the velocity dispersions of their host bulges, M-bh proportional to sigma(alpha), where alpha = 4.8 +/- 0.5. The relation is much tighter than the relation between M-bh and bulge luminosity, with a scatter no larger than expected on the basis of measurement error alone. Black hole masses recently estimated by Magorrian et al. lie systematically above the M-bh-sigma relation defined by more accurate mass estimates, some by as much as 2 orders of magnitude. The tightness of the M-bh-sigma relation implies a strong link between black hole formation and the properties of the stellar bulge.