It seems to be a simple question, but I wasn't really able to find an appropriate answer: How dense is the Milky Way? I am certain that there are reliable statistic, maybe even new ones from the GAIA catalogue?
I am very aware of the fact that the tremendously varies between the core, the bulge, the spiral arms and the inter-arm regions, but I'd like to have a single number for the whole galaxy, something like "a solar system per pc$^3$". Is there anything around?
Thank you very much in advance!