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

Quizplus · Accepted Answer

If spiral galaxies did not contain dark matter, the rotation curves would fall off sharply with increasing distance from the galactic center. This is because the visible matter (stars, gas, dust) in a galaxy is concentrated near the center, and its gravitational influence would weaken quickly with distance. Without additional mass from dark matter to hold the outer parts of the galaxy together, the visible matter alone would not be sufficient to maintain the flat rotation curve observed in spiral galaxies.

Spiral Galaxy Rotation Curves Are Generally Fairly Flat Out to Large