This is such a good and interesting question. 
Presumably the central bank is watching the market and therefore it takes actions. So the real question from what you said is, "can the markets be self regulated?" We already have this answer by Alan Greenspan himself, when he said that there was a flaw of letting the market forces to play out. This is the analogue of hearing Marx saying there was a flaw in his socialist theory. So no, markets can't be self regulated and therefore central banks must regulate. Free economy doesn't work...