sentences:  Theoretical models of supernova explosions suggest that the star that exploded to produce the Crab Nebula must have had a mass of between .Stars with masses lower than are thought to be too small to produce supernova explosions, and end their lives by producing a planetary nebula instead, while a star heavier than would have produced a nebula with a different chemical composition from that observed in the Crab Nebula.Recent studies, however, suggest the progenitor could have been a super-asymptotic giant branch star in the range that would have exploded in an electron-capture supernova.