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 rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round.(c) the orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant.(d) the rotation curve would look the same with or without the presence of dark matter.

A) The orbital speeds would fall off sharply with increasing distance from the galactic center.

Explanation:

The plot of radial distance versus the orbital speed of objects gives us the galaxy rotation curve. The theoretical and practical curves have significant difference. A possible explanation of this difference could be the existence of dark matter.

According to the theoretical calculations the curve should increase sharply and then decrease as the radial distance increases. The theoretical graph does not take dark matter into account. But the plot made by observations shows the plot increasing first then becoming constant as the radial distance increases.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true