Almost all of the hydrogen and helium in the cosmos, along with some of the lithium, was created in the first three minutes after the Big Bang. Two more light elements, beryllium and boron, are synthesized in interstellar space by collisions between cosmic rays and gas nuclei. All of the other elements in nature are formed by nuclear reactions inside stars.

Over the 14-billion-year history of the universe, elements made in stars have been ejected back into space to be incorporated into new stars and planets. Thus there is an intricate relationship between the life cycles of stars and the nucleosynthesis of the elements. Fusion reactions inside stellar cores are exothermic. They release the energy that powers stars and supports them against gravitational contraction. During most of a star’s life, the principal fusion process is the burning of H to form He.

But binding energy per nucleon increases with nuclear...

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