Tbh cores are a really interesting concept I personally see them as pieces of souls or parts of a person's personality or mind that helped shape them as a ghost
Honestly 100%
I've seen a lot of theories about them as well. Some depict them as physical parts of the ghost that "project" their physical forms. Other's see just as you said, pieces of their souls. Honestly it is really up for interpretation, especially if you are doing crossover and want to apply the rules of the other universe.
Personally, I headcanon that ghost cores aren't an inherently physical thing but can take a physical shape in situations. Id image there is a lot of frequency and vibrations going on too, but this is a combo of other explanations. If I remembered who had made the comic about it I would tag them and add the comic but this was years ago.
Definetly a cool concept, if it had been expanded on more in the show I'm sure it would have taken a more supernatural turn rather than super hero but I like it. Leaves a lot up to the fans to decide.
