Black holes are rifts that pass through the layers of reality. They suck matter from the material worlds to The Elemental Chaos and the Negative Energy Plane to be recycled.
The Eye is the largest black hole of them all and sits at the center of the cosmos. While it ultimately resides in the The Elemental Chaos, it also can be reached from Wildspace, and The Ethereal Domain, and is a gaping chasm cutting through all three domains. However, attempting to venture anywhere near the eye via Spelljamming or other similar means of physical travel would be suicidal. Only the most powerful beings in the multiverse can withstand the immense pull of the Eye's gravity.
Everything that passes through the Eye goes to the Negative Plane where it is ripped apart instantly, only to be reassembled as raw energy that erupts out of the Positive Plane. This energy coalesces into the building blocks of matter in the outer portions of the The Elemental Chaos.
The Eye is an important fixture in regulating the balance of energy and matter. It is the gateway to the Negative Plane and its gravity pulls upon all things, including the souls of those who have recently died. They are pulled towards the Eye in a procession called the River of Souls which can be seen in The Ethereal Domain
Orbiting inexplicably at the event horizon of The Eye is the Outlands, and beneath it, the City of Judgement. There, mortal souls are intercepted for judgment and transport to their afterlife in the Outer Planes before they reach the center of The Eye.
Even the Gods and greater Powers have respect for the Eye. It slowly rips material away from their domains in the outer planes. Only through continual rebuilding can they maintain their homes, and thereby their power. This requires raw material in the form of the souls of mortals who have traveled there in the afterlife, then called petitioners. After being rewarded (or tortured) in the afterlife, most petitioners are eventually merged with the outer plane, becoming the raw material that sustains each plane's existence.