Chapter 11, Problem 1RQ

To determine

The general composition of all stars, and difference in composition among stars in terms of elements important to planet formation and life.

Answer to Problem 1RQ

All stars are composed of almost similar composition that is three quarters of hydrogen and one quarter of helium (by mass) and all other elements represents only  a very small proportion of total mass.

Explanation of Solution

All stars are composed of almost similar composition that is three quarters of hydrogen and one quarter of helium (by mass) and all other elements represents only a very small proportion of total mass. All other elements present are star stuffs formed by stars and later released into space when the star dies .

This fact that the star dies also explains the reason why stars vary in their proportions. When the universe was much younger then very old stars were born which means there were only few stars to produce different elements other than helium and hydrogen

Stars that were formed recently including sun were formed from gas clouds that only have $2\%$ of their mass as elements which are heavier than helium. So these elements are very rare and they are important to study planets and life.

Some minimum amount of other elements is necessary for the formations of planets, especially rocky and terrestrial planets such as Earth. Other elements present in the formation of stars such as rocks, metals and ice.

Mostly all the stars are formed of hydrogen and they spent all their lives in generating energy by fusion of hydrogen into helium.

Conclusion:

Thus, all stars are composed of almost similar composition that is three quarters of hydrogen and one quarter of helium (by mass) and all other elements represents only a very small proportion of total mass.