Energy stellar

Helium, plentiful in the cosmos, is a product of the nuclear fusion reactions that are the prime source of stellar energy. The other members of the hehum-group gases are thought to have been created like other heavier elements by further nuclear condensation reactions occurring at the extreme temperatures and densities found deep within stars and in supernovas. 

Abbot, C.G., Radiometer measurements of stellar energy spectra, Astrophys. J., 60, 87-107, 1924. 

It is clear, for example from radio-carbon dating of rocks in the earth s surface, that the solar system must be very much older than the Kelvin age of 3 x 107 years. It is now taken for granted that the main source of stellar energy comes from nuclear reactions. The fusion of four protons (hydrogen nuclei) to an alpha-particle (helium nucleus) is associated with the release of energy Q, where Q k, 26 MeV. The total available energy is thus... 

Fig. 12. Energy levels of leO nucleus near and above the alpha-particle threshold of capture on 12 C. Shown on the right are effective stellar energy regions corresponding to the temperatures given near the three-way arrows. The reaction rate is influenced mainly by the high energy tails of two sub-threshold resonances in 16 O at Er = —45 keV and Er = —245 keV, plus the low energy tail of another high-lying broad resonance at 9580 keV...

The combined mass of two reacting 12 C nuclei falls at an excitation energy of 14 MeV in the compound nucleus of 24Mg. At this energy there are many compound nuclear states, and the most effective range of stellar energies (the Gamow window) at the relevant temperature is about 1 MeV hence a number of resonant states can contribute to the decay of the compound nucleus, and... 

Ter Haar, D (1950) Cosmological Problems and Stellar Energy, Revs. Mod. Phys., 1950 (22) 119-152. 

Eddington AS (1926) The source of stellar energy. Nature 117(Suppl) 25... 

A second component which is responsible for the increased opacity is. the He-ionizing continuum. It may be identified with graphite, which seems to have a "resonance around 25 eV (Taft and Philipp, 1965). The typical size is 0.01 ym and the opacity at 500 A is about <(He) 1.5 x 10 njj. This corresponds to a relative abundance by mass of 2 x 10 , which is about 40% of the cosmic abundance of carbon. Because this component is an efficient absorber only in the He-ionizing continuum, it can absorb about 10-15% of the total stellar energy, which is re-emitted mostly... 

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