No, they are not. For instance, fuzzballs, if they are real, would be black holes from the outside, but not singularities on the inside.

So is this what Fredrik Pohl uses in his Heechee Saga? I always thought that was free fantasizing for the sake of science fiction.

https://en.wikipedia.org/wiki/Beyond_the_Blue_Event_Horizon

Fuzzballs were first proposed as a consequence of superstring theory in 2002, so it would be quite a feat for a scifi author to have come up with them in 1977.

Well, isn't that what being a science fiction author is all about -- predicting the future? :-D

But glad to see Pohl was so great at that too, besides the actual craft of writing.