black holes

If the universe were the skin of an amoeba, possibly of varying thickness and curvature,  hollow and full of space, outside and in, a black hole might be formed when an "isogravitational ring or belt area", unlikely as it might be, became the circumstance where a pinching off of the pseudopodia had almost been completed. The appearance of a black hole might be the relative darkness of seeing the far side of a room through its keyhole from some distance away from the keyhole in the adjacent room.