Fig8_6 Energy generation by two hydrogen burning processes

Fig8_6 Energy generation by two hydrogen burning processes

Fig. 8.6 . The energy output (left vertical axis), in units of power per kilogram or J s-1 kg-1, as a function of core temperature (bottom horizontal axis) in millions, or 106, degrees kelvin, designated K. The proton-proton chain, denoted PP, dominates the hydrogen-burning energy production for the Sun and less massive stars that have lower core temperatures. At the center of the Sun, where the temperature is 15.6 x 106 K, the proton-proton chain is the dominant nuclear reaction chain for converting hydrogen nuclei into helium nuclei, with an energy output 0.016 J s-1 kg-1, or 51 million MeV g-1 s-1 in the units that nuclear astrophysicists employ. In more massive main-sequence stars, the central temperature is higher, and the CNO cycle of hydrogen burning is the most efficient process. Main-sequence stars of mass less than 1.5 solar masses shine by the proton-proton chain of nuclear reactions, while the main sequence stars with mass greater that 1.5 solar masses burn hydrogen by the CNO set of nuclear reactions.

Copyright 2010, Professor Kenneth R. Lang, Tufts University