Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
A)Although dark matter emits no visible light,we have detected its radio emissions.
B)The orbital speeds of stars far from the galactic center are surprisingly high.
C)Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk.
D)Our view of distant galaxies is often obscured by dark blotches,which are presumably made of dark matter.

Question

Quizplus · Accepted Answer

The orbital speeds of stars far from the galactic center are surprisingly high, which suggests the presence of extra mass that cannot be accounted for by visible matter. This extra mass is believed to be in the form of dark matter.

Answer: C
 Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk. This implies the presence of a large amount of dark matter that cannot be directly detected.

Option A is incorrect since dark matter does not emit radio waves that can be detected. Option D is also incorrect since the dark blotches observed in distant galaxies are usually caused by other phenomena such as dust or gas.

Why Do We Believe That Most of the Mass of the Milky