In the 1970s, astronomer Vera Rubin observed that stars at the edges of spiral galaxies were moving just as fast as those near the center. According to Newtonian physics, they should have been moving much slower or flying off into space unless some unseen mass was holding them in place. Galaxy Clusters
It does not interact with electromagnetic forces, meaning it is completely transparent. Dark Matter
Most evidence suggests dark matter is "cold," meaning its particles move slowly relative to the speed of light. 🔭 Key Evidence In the 1970s, astronomer Vera Rubin observed that
The exact identity of dark matter remains unknown, though several leading theories exist: The quest for dark matter with Matt Bothwell In the 1970s