The closest direct hint:
Talk to Dror Ragzlin. Let him cast the Speak With Dead. Take over his mind. Ask who the Absolute is (some question close to that - I can't remember the exact phrase). Note: Save beforehand - you can initiate combat trying this.
I've seen that, too in my playthrough. Seems like the Absolute is just an illusion by a circle of Illithids. Unfortunately... would be cooler lorewise, if she actually was some kind of godess.
