Due to my engineering background, I know just enough physics and mathematics to completely misunderstand general relativity and quantum mechanics. However, one pattern I have noticed is that one favorite past time of physicists is looking at the mathematical models, trying to find insane ass edge cases and then trying to interpret them.
With that in mind, do these equations allow black holes whose singularities extend beyond their event horizons?
If the current accepted theory is predicting negative mass or infinite mass, it doesn't really mean that a physicist deeply believes we are going to be finding particles with negative mass. It's more likely we'll find a better theory.
In some rare cases, these mathematical oddities do turn out to be real. We found equations producing negative energy as solutions long before we discovered antimatter.
This was news in the 90s and it was a plot point in at least two scifi books, though I don't think I can recommend either
This is hypothetical, and not at all "proven" in any meaningful sense.
Upshot is if you spin it fast enough... acgoiawef.awef?