Neither of which would work either, as I already discussed. And "gravitational shock" is not a thing. It would be more just a minor, gradual redistribution of gravitational influence.
But the unbelievables in The Wrath of Khan add up to a far more absurd piece of writing than most Star Trek that preceded it, though sadly not that much of what followed it. That's presumably part of why Gene Roddenberry wasn't fond of it, because he always wanted Star Trek to be smart, scientifically literate, and plausible, within the bounds of budgetary limits and dramatic license.