Question

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?(1 point)
Responses

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

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

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

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.

Answer 1

The correct response is:

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

This observation is critical as the stars at the edge of the galaxy are moving at similar speeds to those in the center, which contradicts the expectation based on visible matter alone. According to Newtonian mechanics, we would expect stars at the edge of a galaxy to move more slowly due to their greater distance from the mass concentrated in the center. The presence of dark matter provides the additional gravitational force needed to explain this phenomenon, suggesting that there is a significant amount of unseen mass within the galaxy.