From the Super Mario Wiki
“What you will get is a Bronze Star. If a Power Star is what you seek, you must reach it by yourself.”
—Cosmic Spirit, Super Mario Galaxy 2
Bronze Stars are items similar to Power Stars that Mario can only get in Super Mario Galaxy 2. They are almost exactly the same as normal Power Stars, except that they are bronze instead of gold and are depicted as being dull and rusty. They only appear if Mario asks the Cosmic Spirit to activate the Cosmic Guide mode. If this happens, the Power Star will immediately become a Bronze Star. The Bronze Stars still add to the Power Star count, but if the player wishes to get a regular Power Star, he or she will have to play through the level without the help of the Cosmic Spirit.
Names in other languages
||Étoile de bronze