http://www.sciencemag.org/news/2018/04/european-satellite-reveals-motions-more-1-billion-stars-and-shape-milky-wayReally interesting about a new satellite's mission.
But the thread title is a pull quote from the article. There are literally hundreds of billions of stars in our galaxy. And we have a VERY limited vantage point.
OF COURSE the galaxy isn't completely mapped. The things that we cannot detect
and likely don't even know exist are exponentially more than the number of stars that we can detect from this limited vantage point.
It ought to be easily understood how limited our understanding of the galaxy is.
However, on to the reason for the quote: "Science" has been claiming a lot of certainty about things
1 lately, so it's not too surprising people might think we already "know" all about what's in the galaxy.
1: Things that we absolutely don't have certainty about, but that's not about to give any pause to the people who "F*ing Love Science!!!"
(edited for clarity)