I understand what you are referring to - one of the proposed mechanisms that prevents time paradoxes in hypothetical time travel scenarios.

The only phrase I can think of is temporal censorship, although I'm not sure if this is the coreect philosophical phrase for the suggested mechanism.

Supernovae are the natural source of heavy element production in the universe. With that being said, if there was a stable isotope of element 115, we'd expect to have discovered it on Earth so I'm very doubtful of Lazar's claims.

White holes are a valid solution to Einsten' field equations with certain constraints applied. If they existed, they would be the brightest objects in the universe. We've yet to observe a white hole so it appears they are a mathematical curiosity rather than a reality.