By the low temperature from 2000 to 3500 Kelvin the maximum of its black body radiation lies inred color gamut, according to the spectral class M as well as the rarer classes R, S and N. Due to its expansion and associated large surface the radiated quantity of light and thus luminosity are high, so that a red giant a bright star orin the specialized terminology a star of large absolute brightness, is. Because of the low temperature and high luminosity red giants are in the right upper range of the Hertzsprung Russell diagram.
With stars middle age (z. B. the sun) becomes inInternal hydrogen converted to helium. In the course of the time the hydrogen supply is however almost used up in the Brennzone of the star, which lets helium cores merge with helium or hydrogen cores.
The elements, which are produced inside the star, thus always becomemore heavily. If the nuclear fusion concerned at the element iron, it stops, since merging two iron cores is an endothermic procedure, D. h., it is set free thereby more energy needed than.
Many Hauptreihensterne become at the end of their development oneRed giants. After end of the hydrogen burning caused contraction the helium burning in the core of the star follows after one by the gravitation. The associated rise in temperature leads to a fast expansion of the outside gas layers on several 100 sun radii. They cool therebyoff and form the visible red shining outer hull of the star.
Due to their expansion the outside gas layers have a very small density and are only weakly by the gravitation of the star bound. Therefore develops in the process of his red giant stage instrong star wind, by which the outside gas layers are completely repelled; they surround it then for some time as planetary nebulas.
- Norbert of long ones: Life and dying of the stars.C.H.Beck'Publishing house, Munich 1995.ISBN 3-406-39720-4.
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