Black holes absorb matter, which ends up somewhere. I have a theory that this matter increases that of the "core" of the black hole, and when it transforms into a white hole, this ejects the matter that previously made up the "core" of the previous black hole Here is a theory i got (i don't know if it's alredy existing, so please tell me if it is) about where the matter goes when it enters a black hole
Woah