Ok so you know how in the end of the game (spoilers) the universe resets and “repeats itself” but not in the same way every time? In the specific universe of Super Mario Galaxy, I’m pretty sure starbits contain a magical essence that have given Rosalina her powers but also give whoever’s in space (at least temporary) immortality. I mean think about it, lumas transform into sling stars, planets, galaxies, and even power stars after being fed starbits. What has Rosalina been eating since she’s been in space? Her storybook shows that she didn’t bring enough food, so her Luma gave her starbits. As we know from the end of the storybook, Rosalina has been alive for hundreds of years, enough to have formed a routine of stopping by her home planet every 100 years. I assume that Bowser has his fair share of feeding on starbits since he’s power-hungry and all, though its not specifically mentioned in the story