Hello, I'm playing a 3 star map, ffa, 4 hard ai's.  I'm in the middle of trying to conquer one of the star systems.  I have already completely wiped out the one enemy ai that had completely dominated the star system.  I wiped out every planet, every structure, and every ship he had on that star system, and he was also wiped out from the game.  Only my empire's presence exists in this star system, but for some reason even though I completely wiped out the enemy, his culture still completely dominates the star system, and I can't colonize a single planet.  The enemy was advent by the way, don't know if it was loyalist or rebel.

So how the heck is it possible for his culture to even exist in this star system?  Does the advent have some kind of ability for their destroyed planets to still generate culture?  Is there anything I can do to repel the culture?  I am vasari loyalist by the way, and I already maxed out my capital ship slots and have a titan but they don't seem to be doing too well with the repelling (they seem to repel a little bit, but not nearly enough for me to colonize anything).  There are no wormholes in this star system if that means anything.  Help please?