Actually my theory, I think
Are black holes really black?
No, we cant see them physically because they're so heavy for their size they sink below the visible horizon. Put a bowling ball on a mattress and it sinks down but you can still see the upper part of the ball. But if the ball is heavy enough it will sink down below the horizontal (visible horizon) of the mattress.
But as you approach the ball you can begin to see it because you're now on the curvature of space created by the ball or black hole. Think of a ship caught in a whirlpool, as the ship approaches the center passengers can look down and see the "black hole". Sound reasonable?