This question is based on this description of the Cormoran Supermassive Black Hole in the Orion Arm's website:
Surrounding this event horizon is an (apparently artificial) accretion disk about 4AU in diameter, which shines due to internal fusion, with a surface temperature of 5700K and a luminosity of 4500 x Sol. This accretion disk is unusually deficient in x-ray emissions, and this made detection relatively difficult; this deficiency cannot be explained naturally, and was the first indication that this object was subject to some form of advanced technological management.
But based on what we know about black holes in real life, can the accretion disk be bright through natural means instead?