I have just found perhaps the biggest thing in the universe: A black hole named SDSS J010013.02+280225.8. It itself is 12 billion times more massive than our sun, and its accretion disk is 439 trillion times brighter. This could mean the universe's biggest habitable zone, right?
Here is the scenario: A black hole identical in dimension to SDSS J010013.02+280225.8 is orbited by co-orbital of trinary star systems within its habitable zone. All the stars are white dwarves, each one only 20% more massive than our sun. Therefore, the "sunlight" comes only from the black hole's accretion disk.
In regards to the black hole's mass, its accretion disk's luminosity and the amount of X-rays being emitted, how far and how wide would the habitable zone be?