In the picture of the universe each one of those dots is not a galaxy! Each dot is a super-cluster having 100 to 1000 clusters. Each cluster is 100s-1000s of galaxies! On an average a galaxy is 100,000 to 600,000 light years across having about 100 to 1000 billion stars. One light year is about 9461000000000km. …Aaaand that’s only the stuff we can see! Notice the Milky Way in the center, that because that picture is of the observable universe (us in the center and looking all around). The entire universe could be even bigger — 3 x 10 to the power 23 times bigger (almost a trillion trillion times big). You think the universe is huge? No, it’s actually far far far bigger than that!