Question

stars in the outer parts of the milky way

• orbit more quickly than expected based on the amount of luminous mass.
• are younger than expected based on the cold dark matter model of the universe.
• should be brighter than they are observed to be if current stellar evolution theories are correct.
• have a much lower metallicity than expected based on the galaxys age.

Explanation:

Stars in the outer parts of the Milky - Way orbit more quickly than expected based on the amount of luminous mass. This is a well - known problem related to the presence of dark matter. The other statements are not accurate in the context of current astronomical understanding.

Answer:

Stars in the outer parts of the Milky Way orbit more quickly than expected based on the amount of luminous mass.