Nebular Supernova – Crab Nebula. The Crab Nebula represents a violent supernova explosion of a star (likely a third, fourth, or even later-generation star). Heavy elements with atomic weights greater than 26 (and some with lesser atomic weights between oxygen and iron) were likely generated during this explosion. Which element probably formed in a supernova? You may want to refer to a periodic table. Choose one: gold (Au) carbon (C) hydrogen (H) helium (He)