Another important clue that convinced scientists that dark matter was real was the observation that it can bend light. This is called gravitational lensing. Astronomers would sometimes look out into the sky and spot something strange. They would see the image of a galaxy coming from one direction. There’s nothing weird about that, but if they moved the telescope a tiny bit, they would see the image of another galaxy that looked very similar to the first galaxy. The shape, the color, and the light that came from these galaxies were so similar, astronomers were sure they were the same galaxy.
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