Where did the different chemical elements come from?
<p>When hydrogen in the core of a star is exhausted, the star begins to contract and heat up as a result. If the star’s mass is insufficient, it will simply shed its outer layers of material, leaving only a core consisting of helium (a helium white dwarf). Still, if the star’s mass is large enough, the next cycle of nuclear reactions will begin, in which helium is converted into carbon and oxygen.</p>
<p>When helium is exhausted, the compression will repeat, and depending on its mass, the star will either shed its outer layers of material, leaving a white dwarf, or carbon and oxygen will begin to burn. Successively heavier elements may ignite until…</p>
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