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pp chain vs CNO cycle

What you are seeing: the two main hydrogen-burning networks in stellar cores, with their energy-generation rate compared across temperature. The pp chain (left) goes as ε∝T4\varepsilon \propto T^4; the CNO cycle (right) goes as ε∝T17\varepsilon \propto T^{17}. The cross-over is near 1.8×1071.8 \times 10^7 K. The Sun (T_core = 1.55×1071.55 \times 10^7 K) is about 99% pp; an O-star is essentially 100% CNO

Figure 1. pp-chain (left) and CNO-cycle (right) reaction networks; live pp/CNO contribution as a function of core T; Q = 26.73 MeV per net synthesis. Method: epsilon_pp ~ T^4, epsilon_CNO ~ T^17, normalized so the Sun is 99% pp.
core T (10^7 K)1.55
presetSun
animation speed2

WHAT TO TRY

  • Vary each control and watch the rail readouts respond.
  • Compare the diagnostic plot against the live scene.