NUCLEOSYNTHESIS IN AGING STARS
Graphic summary of the evolution of variously sized stars, showing their birth, middle age and eventual demise; from the Chandra X-Ray telescope site. Image credit: NASA/CXC/M.Weiss.
Light Echoes From Red Supergiant Star V838 Monocerotis - December 2002, from the Hubble site
The primordial nucleosynthesis of the big bang provided just enough energy to form Hydrogen and Helium, the two lightest elements. All the heavy elements were cooked up much later by nucleosynthesis in aging stars. Joseph Silk (1994: 19) writes:
The production of carbon in stars is the secret of life: the carbon in our bodies formed aeons ago from the triple alpha process inside supergiant stars that are now dead.
As the core begins to burn helium, its luminosity dramatically increases. The outer layers of the star swell up like a baloon, and the star becomes a red giant. Our sun, for example, is destined to become a red giant in about five billion years, and the earth will then be enveloped inside the fiery stellar atmosphere. Helium burns at about 100 million degrees Kelvin to form carbon, and even heavier elements are formed by massive stars in their later stages of evolution.
Silk, Joseph. (1994: 160) A Short History of the Universe. Scientific American Library, New York.
A star's life cycle is determined by its mass. The larger the material available in the nebula, the shorter, and more spectacular, the life of the star