Introduction to Astronomy The Solar System
Introduction to Astronomy The Solar System ASTR 101
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This 3 page Class Notes was uploaded by Torrey Lynch on Sunday October 25, 2015. The Class Notes belongs to ASTR 101 at University of North Carolina - Chapel Hill taught by J. Rose in Fall. Since its upload, it has received 25 views. For similar materials see /class/228835/astr-101-university-of-north-carolina-chapel-hill in Astronomy at University of North Carolina - Chapel Hill.
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Date Created: 10/25/15
SUMMARY FOR OCTOBER 27 CLASS Topics Covered 1 Future Evolution of the Sun Summary for Each Topic 1 What happens when after 10 billion years the Sun has exhausted its available fuel supply of hydrogen in its core We can speculate that perhaps one or more of the follwoing things can happen a the site of hydrogen to heliurn fusion moves from the core to another location b another fusion process involving heliurn starts up to replace hydrogen to heliurn fusion as the energy source c when fusion ends the Sun will cool It will then either collapse completely or it is maybe saved from collapse by the emergence of a new form of pressure that can occur at very high density In fact all of the above takes place at some level The main point to keep in mind is that throughout the Sun s late evolution it tends to become increasingly divided in personality between a progressively srnaller denser hotter core and a larger lower density cooler envelope As 4 H nuclei are replaced by a single He nucleus the pressure in the core drops which is further exacerbated as H to He fusion stars to wind down and thus the core will contract and further heat up Eventually the core becomes so hot that the temperature in the still hydro gen rich layer surrounding the core becomes hot enough for nuclear fusion of H to He to commence It in fact takes place at an even greater rate than before which pumps extra heat energy into the surrounding envelope which then expands and cools The result is a red giant star We discussed evidence in class that such red giant stars exist Speci cally if you make a lot of the lumi nosities of neaby stars versus their surface temperatures you nd that most of them lie along a principal sequence in this so called H R diagram with the more luminous and hotter stars being the more massive ones and the less luminous and cooler redder stars being less mas sive ones All of these main sequence7 stars are deriving their energy from H to He fusion in their cores How ever there are also stars int he upper right corner of the H R diagram the red giant stars which represnt stars in the advanced stage of evolution discussed above We looked at the equation relating luminosity temperature and radius to see that a very luminous star with alow surface temperature must have a huge radius L 47TR20T4 where L is luminosity R is the radius and T is the sur face temeprature of the star We followed the various evolutionaty stages that the Sun will go through which are summarized in stellarpdf ending with the core becoming so dense that a new kind of prssure called degenerate electron pressure comes into play and prevents the Sun from collapsing any fur ther This degenerate electron pressure is an effect of the quantum theory of matter and represents a basic resistance of electrons against being packed too closely together In this way the Sun ends its life as a slowly cooling White dwarf7 star A pictorial representation of the Sun s evolutionary stages is given in Figures sun evolution001jpg and sun evolution002jpg