The stars at the edges of a galaxy are rotating around the galaxy’s center at the same speed as the stars in the middle of the galaxy. How does this provide evidence of dark matter? Dark matter absorbs light from outside the galaxy, allowing the light of the stars in the galaxy to show the orbital speeds of the stars.

Dark matter emits the light that astronomers need to see the orbital speeds of the stars.

Dark matter subtracts gravity, which allows the stars to rotate at the same speed.

Dark matter provides the gravity that allows the stars to rotate at the same speed.