Dark Matter Is in Our DNA
While some point to galaxy cluster work by Fritz Zwicky in the 1930s, dark matter was truly “discovered” in the 1970s by Vera Rubin, who was studying the rotation of spiral galaxies. Rubin found that galaxies were spinning too fast for the matter we could see in them, yet they weren’t flying apart. Rubin’s work left astronomers with a choice: Either our laws of gravity were wrong, or there was something else out there pulling on the galaxy’s stars and speeding them up while keeping them together.
Since physicists had already invested a few centuries on their theories of gravity, few of them signed up for the first conclusion. In that way the astrophysical community moved en mass toward the second idea: There was another kind of stuff out there we couldn’t see that was exerting a gravitational force on the stuff we could see.