The final radius of a protostar r2 is a function of its mass and initial radius r1: gm where-b-4.5 ev and ε,-13.6ev a. from the expression of the jeans mass and jeans radius, derive an expression for the jeans density. for a jeans density of 10-16kg. m-3 plot the initial radius of protostars between 0.2 and 2 solar masses on a different graph, plot the final radius of the same protostars. b. c.