HYDROGEN "BURNING" (PROTON-PROTON CHAIN)
A star's energy comes from combining light elements into heavier elements byfusion, or "nuclear burning".
In small stars like the sun, hydrogen burning is the
fusion of 4 hydrogen nuclei (protons)
into a helium nucleus (2 protons + 2 neutrons).
Forming helium from hydrogen gives offlots of
energy (a natural hydrogen bomb).
Nucleosynthesis requires very high temperature. The minimum temperature for hydrogen fusion is 5 million degrees.