Class 9 Homework-

Dark matter is suspected to exist in the universe because:
A. the night sky is dark between stars
B. the orbital period of stars in the outer parts of a galaxy is greater than the orbital period
of stars near the galactic center
C. the orbital period of stars in the outer parts of a galaxy is less than the orbital period of
stars near the galactic center
D. the orbital period of stars in the outer parts of a galaxy is about the same as the orbital
period of stars near the galactic center
E. all galaxies have about the same mass




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