Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different?
A) The orbital speeds would fall off sharply with increasing distance from the galactic center.
B) The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant.
C) The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round.
D) The rotation curve would look the same with or without the presence of dark matter.
Question 2
What observational evidence supports the galactic fountain model (which describes how gas cycles between the disk of the galaxy and regions high above the disk)?
A) We have discovered a jet of ionized gas shooting out of the bulge of our galaxy.
B) We have discovered that the entire galactic disk is being uniformly rained on by cool gas coming from the halo.
C) We see hot gas high above the region of the disk near our solar system, along with cool gas that appears to be raining down from the halo.
D) We have observed a lot of water molecules in the interstellar medium.
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