A star, which is $2\mathrm{.}1{10}^{20}m$ from the center of a galaxy, revolves around that center once every $2\mathrm{.}8{10}^8$ years. Assuming each star in the galaxy has a mass equal to the Sun's mass of $2\mathrm{.}0{10}^{30}kg,$ the stars are distributed uniformly in a sphere about the galactic center, and the star of interest is at the edge of that sphere, estimate the number of stars in the galaxy.