from Foundations of Black Hole Accretion Disk Theory https://link.springer.com/article/10.12942/lrr-2013-1 https://link.springer.com/article/10.12942/lrr-2013-

from Foundations of Black Hole Accretion Disk Theory https://link.springer.com/article/10.12942/lrr-2013-1 https://link.springer.com/article/10.12942/lrr-2013-1 > The radiation we receive from quasars and microquasars comes not from the black holes themselves, but instead originates in the accretion disks which surround themFootnote6 (see Figure 1). In these accretion disks, angular momentum is gradually removed by some presumably (although not necessarily [48]) dissipative process, causing matter to spiral down into the black hole, converting its gravitational energy into heat, and then, by various processes, radiating this energy.Footnote7 The radiation subsequently leaks through the disk, escapes from its surface, and travels along trajectories curved (in space) by the strong gravity of the black hole, eventually reaching our telescopes. So not fusion, the energy is gravitational potential.