My non-professional opinion on black holes is that they are simply the result of gravity, are completely symmetrical, extremely stable, and extremely long-lived. I don't buy the wormhole concept, because a BH is always a local event, ruled by gravity to contract, and stay contracted. There is no denser place in the universe than inside a BH. It is as packed together as is possible, and therefore simply cannot "go" or lead to anywhere else. If there are higher dimensions involved, it's beyond our understanding, and explanation. Their life is so long, we might as well consider them immortal, certainly in human terms. I think they keep the universe anchored.