 Besides mass , the elements heavier than helium can play a significant role in the evolution of stars . Astronomers label all elements heavier than helium " metals " , and call the chemical concentration of these elements in a star , its metallicity . A star 's metallicity can influence the time the star takes to burn its fuel , and controls the formation of its magnetic fields , which affects the strength of its stellar wind . Older , population II stars have substantially less metallicity than the younger , population I stars due to the composition of the molecular clouds from which they formed . Over time , such clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres . 
