I did stellar collisions type of stuff - well we were looking for that but the data was more indicative of the prevalence of binary mergers in star clusters than it was of collisions (I concluded collisions don't happen as much as they originally thought).
In Canada, you enroll for a Master's, do that for two years, tehn you enroll for a PhD. No one applies directly for a PhD out of undergrad - it goes master's, then PhD but sometimes a supervisor will allow their student to not do the defense and just carry the same project into the PhD. It is different in every country though. In England, you can have you PhD by the time you are 25. No one respects you or anything, especially in North America, but they still call you Dr. In fact, if you want to come over to Canada with an English "PhD", we call that your Master's degree and then you start your PhD.