Are we made of stars?

Carbon, nitrogen and oxygen atoms in our bodies, as well as atoms of all other heavy elements, were created in previous generation of stars over 4.5 billion years ago. Because humans and every other animal as well as most of the matter on Earth contain these elements, we are literally made of star stuff, said Chris Impey, professor of astronomy at the University of Arizona.

This reaction continues in stars today as lighter elements are converted into heavier ones. Relatively young stars like our Sun convert hydrogen to produce helium, just like the first stars of our universe. Once they run out of hydrogen, they begin to transform helium into beryllium and carbon. As these heavier nuclei are produced, they too are burnt inside stars to synthesise heavier and heavier elements. Different sized stars play host to different fusion reactions, eventually forming everything from oxygen to iron. Eventually at iron, there is no energy released at all. And for elements beyond iron more energy is need for fusion than gravitational pressure can provide.