Final answer:
Observations of Zwicky, Rubin, and Ford suggest the existence of dark matter due to the velocity variations in stars orbiting galaxies, the rotational speeds of spiral galaxies, and the mass distribution of galactic clusters.
Step-by-step explanation:
The observations of Zwicky, Rubin, and Ford suggest the existence of large quantities of dark matter for the following reasons:
- Zwicky's measurements of the velocities of stars orbiting the galaxy showed that the velocity varied with distance from the center of the galaxy. This implies that there is a tremendous amount of matter in the galactic halo, as the velocity curve is almost flat instead of decreasing as expected if the mass was concentrated in the center.
- Rubin's investigation of spiral galaxies found that their outermost reaches were rotating as quickly as their centers, which would cause them to fly apart unless there was a significant discrepancy between their observable matter and their actual matter, suggesting the presence of dark matter.
- Studies of galactic clusters have also indicated that galaxies have a mass distribution greater than that obtained from their brightness, which extends into large halos surrounding the luminous parts of galaxies.