How do you get to the star world in Super Mario galaxy?

Answer 1

All you have to do is get 70 stars form the worlds you have opened so far, then you go to Bowser's Galaxy Generator, do the mission, and defeat Bowser by

ground-pounding the meteorite after punching the planet. After you do that a few times, he will cough up the star, and you have to try to ground pound the meteorite into him again about four or five times. f you can do that, get the star, go past the cut scene and credits, and reopen your save file, the star world will open.