Abstract

Accretion onto black holes, a process once thought to be an exotic sideplot in the story of the Universe, is now understood to be an important theme. Although accreting black holes are comparatively rare, they are so efficient at producing light that their total emission, integrated over a Hubble time, is only one order of magnitude smaller than that of all the stars in the Universe [22]. Moreover, the strong correlations between the masses of black holes in galactic nuclei and the mass and binding energy of the bulges of the galaxies housing them (e.g., as summarized in [3]) demonstrate that the growth of these black holes is tightly coupled to the growth of the surrounding stellar bulge; in other words, mass accretion onto black holes is an integral part of the construction of galaxies.