at the centre of any black hole is matter which has been compressed so that the various subatomic particles are squeezed tightly together. In this state our normal calculations fail to operate properly to model what is going on with respect to time but one thing is certain - a black hole is not and never will be a "portal", "wormhole", "hole in space" or any other science fiction bullshit.
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At the centre of a supermassive black hole is a supermassive singularity, that is shielded from us. If my understanding of black holes is correct, there is no matter as such in the singularity, as there is no room for any matter - all (current) theories in physics break down at the centre of a black hole so we cannot say what occurs there... (Even Prof Hawking has changed his opinion on what happens there, recently)
One thing that Prof Hawking has said that he has not changed his view on, I reckon, is that eventually a black hole will vanish in a puff of X-rays, but any massive or supermassive singularity, is going to last for a very long time, much longer than the lifetime of the universe to date... This means that the ultimate fate of all the matter in the universe, is going to be as part of a very thin 'soup' of electrons and positrons, which are so remote from each other that they will never meet each other to mutually annihilate.... the whole thing existing at a minute fraction of a degree above absolute zero...
One thing that Prof Hawking has said that he has not changed his view on, I reckon, is that eventually a black hole will vanish in a puff of X-rays, but any massive or supermassive singularity, is going to last for a very long time, much longer than the lifetime of the universe to date... This means that the ultimate fate of all the matter in the universe, is going to be as part of a very thin 'soup' of electrons and positrons, which are so remote from each other that they will never meet each other to mutually annihilate.... the whole thing existing at a minute fraction of a degree above absolute zero...