When Mario gets a star he will become invincible for a short time and you'll hear the Invincible BGM tune. During this time you are immune to all enemies, and the only thing that can kill you is falling off the screen.
The title comes from the Famicom 20th Anniversary Original Sound Tracks Vol.1 album.
Super Mario Bros. (NES)
This song plays very rapidly, and sounds really crazy when you're running out of time. Both versions of the song loop.