Let's talk a little bit about our galaxy. You probably know that it's a spiral galaxy, with several "arms" reaching out from a central bulge, and is shaped like a disk. Most of our galaxy's mass is centered in that central bulge, with is about 13,000 light-years from top to bottom (which is really, really big), and has a density of around 1,600 stars per cubic light-year. To put that in perspective, out where we are in the Milky Way it's only a few thousand light-years thick (which is still really big), and the stellar density is closer to 0.004 stars per cubic light-year.