Curious about Krypton’s famous fate, I once looked up “exploding planets.” Apparently, there’s no known mechanism that can cause this to happen. Of course, the key word is
known - and sci-fi authors are free to invent something rare or mysterious.
In my view, the more fantastic the sci-fi tech or phenomenon, the less it should be explained. So if the plot requires a planet to explode, maybe mention “phlebotinum” (or some such) as the cause. No one can challenge this because “phlebotinum” is nonsense. When you try to make the science seem more authentic (by using known terms like pulsar) you actually make it
less authentic.