Julie Ohnemus, age 13, of Des Moines, Iowa, for her question:
What are the stars made of?
The stupendous stars are blazing nuclear furnaces, but they are made of assorted atoms, the same chemical elements that build all the solid, liquid and gaseous matter in the entire universe. Some have more of this and less of that element. And many of their gaseous elements occur in frozen form right here on the earth. However, our percentage of hydrogen is very small and every star needs enormous supplies of this gas to fuel its furnace.
The recipe for building an earth type planet contains about 92. different elements, each made from atoms of the same type. Most of the ingredients are durable, medium weight atoms that freeze solid in earth type temperatures. A very few form liquids and others remain in their gaseous states at these temperatures. A few heavier atoms are created during radioactive decay. Nuclear physicists say other elements exist, but their heavy atoms are too unstable to live more than a moment.
This assortment of known and unknown basic elements provides the ingredients in the blazing stars. But there the coolest temperatures soar to thousands of degrees and all elements are too hot to reach the solid, or liquid states of matter. They are blazing gases. And it so happens that in this form the elements a star are easier to identify across the vast distances of space.
The spectroscope has lenses and mirrors to analyze incandescent gases and each different element makes its identifying marks on the rainbow spectrum of light. This is how we know the ingredients in a star. In all cases, the two major ingredients are hydrogen and helium. Most of the other known elements have been detected in the average star, though altogether they make up less than one hundredth part of its material. However, there are variations even in the average or main sequence stars, most of which are fairly similar to our sun.
It seems that the chemical composition of a star varies somewhat with temperature and temperature also creates a variety of starry colors. The colors provide clues to energy output, which is related to the rate at which a star is burning. Actually it consumes its original hydrogen fuel by atomic fusion, which releases nuclear energy as it converts the hydrogen fuel into helium ash. White dwarfs are white hot and made mostly of helium. Certain younger stars seem to contain more metallic elements though usually not more than one per cent of their total material.
It now seems that new stars are forming while ancient ones die. The chemical composition of each star appears to be related to its life story. At birth, it was composed almost or perhaps entirely of hydrogen, the lightest of all elements made from the smallest of all possible atoms. This changes as nuclear fusion converts the hydrogen fuel to helium. The evidence indicates that our average starry sun has taken perhaps five billion years to convert about half of its original hydrogen into helium.