It is the 12th most abundant of all elements. It is the 3rd most abundant among the elements that have odd atomic numbers. The only stable isotope of aluminium is aluminium-27. It is the 18th most abundant nucleus in the Universe. It is created after fusion of carbon in massive stars that will later become Type II supernovae: this fusion creates magnesium-26, which, when capturing free protons and neutrons becomes aluminium. Essentially all aluminium now in existence is aluminium-27; aluminium-26 was there in the early Solar System but is now extinct. The trace quantities of aluminium-26 that do exist are the most common gamma ray emitter in the interstellar gas.