What observations led to the proposal of Dark Matter? Typically in science, you do not come up with an extension of your theory or propose a new hypothesis unless new data contradicts existing ideas.

Explanation:

Two teams of astronomers observed in 1988 that the universe was accelerating in expansion. They proposed that a phenomenon known as dark energy could be responsible for the development. They came to this conclusion by measuring lights emanating from exploding stars called type 1A supernovae.