ASTR 101 1st Edition Lecture 28 Outline of Last Lecture I Low mass stars II Life stages of low mass stars Outline of Current Lecture I Life track of a sun like star II Life stages of high mass stars III High mass stars make elements necessary for life Current Lecture I II II Life track of a Sun like Star a Our Sun is a low mass star Once hydrogen is completely exhausted it will evolve from the main sequence It will eventually become a white dwarf Life stages of a high mass star a The core in a high mass star is even hotter than in a low mass star There is only proton proton collision in low mass and now we have hydrogen atoms colliding with helium using carbon nitrogen and oxygen as catalysts A greater core temperature enabled H nuclei to overcome greater repulsion b This is done through the CNO cycle The net effect is still converting 4 protons into 1 helium c Life stages of high mass are similar to that of low mass stars but high mass stars evolve very fast compared to a low mass star i Hydrogen core fusion in the main sequence ii Hydrogen shell fusion as a supergiant iii Helium core fusion also as a supergiant iv This time we will have other elements burning on the shell as well High mass stars make elements necessary for life a The force of gravity in a high mass star keeps its carbon core so hot that degeneracy pressure is not a factor Once helium fusion stops gravitational contraction of carbon core continues until the core reaches 600 million K which allows carbon to be fused into other elements b Gravitational equilibrium is temporarily restored by carbon fusion carbon fusion continues until it is depleted once again and still more elements are able to be formed This struggle between the star and gravity will eventually result in the formation of new elements These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute c d e f Multiple shell burning near the end of the star s life its inside contains layers of different each fusing a different element iron piles up in the silicone fusing core toward the very end Core temperatures in stars with greater than 8MSun allow the fusion of elements as heavy as iron Iron is unique it is not possible to generate nuclear energy from Iron which has the lowest mass per nuclear particle Iron appears to be the most stable element and elements heavier than iron are not produced in stars There is a higher abundance of elements with even numbers of protons How does a high mass star die Through a Supernova explosion