Illustration: Alan Stonebraker; solar neutrino image courtesy Robert Svoboda, Louisiana State University; Sirius and Betelgeuse images from NASA/Hubble Space Telescope

Figure 2: The main energy production processes during stellar hydrogen burning and helium burning. (Top left) the $pp$ reaction, which controls the main energy production in low-mass main sequence stars like our sun (neutrino image, bottom left). (Top center) the first CNO cycle as main energy source in massive main sequence stars such as Sirius (shown at bottom center). (Top right) the main reactions of stellar helium burning such as the triple $α$ process and the subsequent $α$ capture on $12C$, which control the energy production for red giant stars such as Betelgeuse (bottom right).