Spiral arms appear bright because ________.
A) they contain far more stars than other parts of the galactic disk
B) they are the only places where we find stars within the disk of the galaxy
C) they contain more molecular clouds than other parts of the disk
D) they contain more hot young stars than other parts of the disk
Question 2
What evidence suggests that most of the mass of the Milky Way is in the form of dark matter?
A) The orbital speeds of stars far from the galactic center are surprisingly high.
B) 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.
C) Although dark matter emits no visible light, we have detected its radio emissions.
D) Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter.
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