ASTR 1P02 Lecture Notes - Main Sequence, Event Horizon, Reaction Rate
31 Jan 2013
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Document Summary
First red giant stage of a medium mass star (m= 0. 5 m-8m: non-fusing he core which shrinks and heats up, hydrogen is fused into helium (hydrogen fusing shell, non-fusing hydrogen over layer. Because of its proximity to very hot he-core the rate of hydrogen fusion in hydrogen fusing shell is greater than the fusion rate during the main sequence phase. The energy transport to the surface cannot catch up with all that energy produced in the fusing shell and the thermal pressure builds in the interior of the star. This pressure causes the star to expand. Increase in the surface area causes the surface temperature to drop and its color changes from white yellow to orange or red. When the temperature of the shrinking helium core increases to 100 million. K the helium nuclei start fusing into c12 (and some o16) nuclei with the release of energy (so-called helium flash)
