Estimating Number of Stars in Milky Way Galaxy: Kepler Problem Solution

[CinderBlockFist]

Our Sun, with mass 2.0 1030 kg, revolves about the center of the Milky Way galaxy, which is 2.2 1020 m away, once every 2.5 108 years. Assuming that each of the stars in the galaxy has a mass equal to that of our Sun, that the stars are distributed uniformly in a sphere about the galactic center, and that our Sun is essentially at the edge of that sphere, estimate roughly the number of stars in the galaxy.

How can i find this answer if the stars don't fill up the space because they are spheres?

 

[dextercioby]

Compute the galaxy's mass and divide it to the mass of the sun (i assumed that the average mass of a star is roughly equal to the one of the sun).

Daniel.

 

[HallsofIvy]

It doesn't matter that the stars don't fill space. Treat it as if all mass were concentrated at the center of the galaxy.