We know that stars are the factories that gave the universe the elements of the periodic table. Well, this is not entirely true, but nearly so.
In fact, nearly 13 billion years ago our very hot universe was already cooling down enough to allow electrons to recombine onto protons to make the first hydrogen atoms. These elements are said to have an atomic number of one. In addition to this element which wins the prize for being the first recognizable element in the universe, also helium atoms with an atomic number of two, and trace amounts of lithium and beryllium recombine from the cooling gas.
The first stars in the universe were made mostly of hydrogen, similar to all stars today. The first stars were also responsible for creating elements other than beryllium, same as all stars today.
These element-making factories require extremely high temperatures and pressures in excess of 100 million degrees which can only be found deep in the core of a star. On the topic of making a multitude of elements, the bigger the star the better. In the ideal example of a star much more massive than the Sun, the other elements are made by the combining of two or more helium nuclei. Each time a new helium nucleus grabs another helium nucleus, the atomic number increases by two.
In this way, elements with even numbered atomic numbers like carbon, oxygen, and silicon are expected to be more common today than elements with odd numbered atomic numbers. This theoretical expectation can be tested by measuring the relative amounts of the chemical elements in the Sun and other nearby stars. When observational astronomers go out and make such tests, their findings agree with this expectation.
Although indirect, this agreement is interesting because it is the only way we have to test our knowledge of the activities that take place in 100 million degree environments!
