Here's my attempt at making up a 'fun' problem for all our math folks. If you look diametrically opposite where you are standing on the outside rim of a relativistic merry-go round, you will see the greatest degree of Lorentz length contraction (distance contraction between the ponies or the stars), compared with the ones on the same side of the rim as you are. First, satisfy yourselves that this is the case, and then tell us, what would be the effect of said contraction on your perception of the gravitational pull of those billions of stars being smooshed together in an area far beyond the black holes in the center of the galaxy? Does it make any difference that you can't actually see the contraction? How does this square with the late Vera Rubin's observation of the anomalous rotation profiles of spiral galaxies? Could this effect explain the additional gravitational pull she attributed to "dark matter"?