AST 341 Lecture Notes - Lecture 10: Stellar Structure, Black-Body Radiation, Quasistatic Process
23 Dec 2016
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Document Summary
We have learned so far that a star is a radiating gaseous sphere, made predominantly of hydrogen and helium. This mixture of gas is governed by frequent collisions between its particles, ions, electrons, and photons as well. Frequent collisions lead to a state of ther- modynamic equilibrium, which is characterized by a temperature, indicative of the energy distribution of the particles. For example, a free ideal gas in thermodynamical equilibrium is described by a maxwellian velocity (kinetic energy) distribution. It is thus described by a temperature distribution t (r). This function can also be a function of time. However, the condition of thermal equilibrium is still maintained if the time elapsed between collisions - the so-called mean free time - is much shorter than the timescale for change of macroscopic properties. Equilibrium between matter and radiation can be achieved as well, by collisions (in- teractions) between mass particles and photons.
