ASTR 1P02 Lecture Notes - Lecture 4: Hydrostatic Equilibrium, Main Sequence, Thermostat
8 Apr 2016
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Document Summary
Once a star becomes a main sequence star it is in hydrostaic equilibrium. The force of gravity which is compressing the star is balanced by the outward gas pressure from within the star. The pressure and the temperature increase"s with depth. Hydrostaic equilibrium is maintained through pressure-temperature thermostat. If the rate of the hydrogen fusion in the core goes up, the pressure and temperature will increase. Increased pressure pushes out the top layer and the star expands and cools. The luminosity of main sequence stars increases slowly over ime, The present luminosity of the sun is l = 4 10^26 wats. It is about 30% higher than what it was when it became a main sequence star. To maintain the stars pressure (p), in order to support the top layers, with decreasing n the temperature (t) has to increase over ime.
