I wasn't thinking a dev response was really all that necessary
I don't think there is any official lore about how it does whatever it does. It's probably not the sort of nuclear weapon we produce simply because the power of our weapons drops off exponentially with distance and we're talking about a pretty big area of space here. It would have to be a pretty enormous charge, and what the game shows it doing to planets (without benefit of a point-blank or on-contact detonation, even) ... yea, it would be funny to see the math on how big a modern nuclear weapon would have to be to actually
fracture the Earth when detonating 100km from the surface.
So maybe it's the "completely liberating" sort of "atomic" reaction where the
entire energy (E=mc^2) of the atoms in the payload is released. That would probably still need to be a stupidly big bomb.
So it just makes things go
emphatically boom in some kind of nucleary fashion, but MkV ships are constructed from cockroaches and are thus immune