Science
Spinning galaxies gave the first strong evidence dark matter is real
In the 1970s, Vera Rubin and Kent Ford measured how fast stars orbit at different distances from a galaxy's centre. If only visible matter existed, outer stars should orbit slower — instead, across more than 75 galaxies, they moved just as fast as inner ones. The only explanation was a halo of unseen mass far outweighing everything astronomers could actually see.