AST 341 Lecture Notes - Lecture 11: Virial Theorem, Hedeby Stones, Net Force

• School: Stony Brook University
• Department: Astronomy
• Course: AST 341
• Professor: Rosalba Perna

Document Summary

Let"s consider an isolated, spherically symmetric, static star. Let"s derive these equations one by one: conservation of mass. Let r be the radial coordinate in the star, and (r) the density as a function of radius. Let"s consider an annulus of thickness dr at a distance r from the center, and let dm be the mass enclosed by the annulus. If there are no sources or sinks of mass in the annulus, one can write dm = 4 r2 dr dm dr. We have seen that, for most of its lifetime, a star can be assumed to be in thermal equilibrium, i. e. at each radius the gas is neither heating up nor cooling down with time. Let q be the rate of energy generation per unit mass (with units erg s 1 g 1) and let"s again consider an annulus of thickness dr at a distance r from the center.