I'm beginning to find out a little bit about the basic idea. It seems to be a lot to do with the angular momentum of the growing black hole. Sufficient angular momentum seems to turn the event horizon into a "doughnut". further increase brings the "top" and "bottom" together so that the doughnut ceases to exist. Eureka! a sort of B H from which light can escape.

All this happens in theory, though.

I'm a long way from being sure how the angular momentum achieves all this.

There never was nothing.