Pretty sure it would dissipate by then...For the sake of argument.
What if that Powerful flash thingy caused a planet to decimate, if by chance it was aimed at a distance planet that by chance is like in the movies watching us to break the warp speed and talk to us, instead they come here finding revenge for we blow up on of there sister planets by chance again, just messing with things we dunno.
now the alien outpost on pluto, on the other hand...
