Question

I know that there's no evidence at this point for "white holes" however would it even be mathematically possible for a black hole to be connected to a white hole (total opposite so everything would be expelled, after some really extreme physical conditions)? Maybe with a wormhole connecting them? If this was even possible (if the black hole or connection could actually be created and be stable enough), would that matter be expelled into a different universe, etc? Maybe even a different region of spacetime? Just curious, as it would be a cool idea.

Answer 1

white holes are microscopically the same objects as black holes, and it's guaranteed - by the second law of thermodynamics - that all macroscopic processes occur in the way as they do in black holes and not white holes (the latter are time-reversed of the former).

However, if you don't care about the second law of thermodynamics that prevents black hole size from shrinking by emitting large objects (which objects?), then you may write down any configuration in general relativity you want. In particular, it's easy to connect white holes to black holes. After all, an "eternal black hole" is a solution that is doing nothing else.

The connection between a white hole and a black hole goes in a different direction than you seem to expect, however. It's a connection between the past and the future. It's because the (neutral) white hole singularity is a spacelike singularity in the past, and the (neutral) black hole singularity is a spacelike singularity in the future. To connect those singularities, you need timelike (rather than spacelike) trajectories.

One doesn't need any wormhole to write down an eternal black hole. It may sound cool to combine so many different holes but it is totally unnecessary: the wormholes are independent objects from the black holes and white holes.