The Beanstar was a mystical object of great power, touted as the granter of wishes. This power was what drew Cackletta into stealing it. However, the star was cast into a deep sleep and can only be awoken from this slumber upon its hearing of the most beautiful voice, which is that off Princess Peach. If one attempts awake the star with a different voice the Star will become furious and go on a rampage, which resulted in it breaking apart. In Mario & Luigi: Superstar Saga, the Beanstar is broken into four pieces which Mario and Luigi set out to find at one point in the game.
The Star generally resides in Beanbean Castle and is surrounded by a barrier, which can disabled by fixing the plumbing in the basement of the Castle.