Astronomy: The Universe Online Practice

Question

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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 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 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 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.
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.
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Answer 1

The correct response to the question is:

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

This finding suggests that there is more mass in the galaxy than what we can observe with visible matter, as the expected rotation speeds based on visible matter would decrease with distance from the center. The presence of dark matter helps explain the consistent rotation speeds of stars at varying distances from the galactic center.