Recently, Astronomers Have Observed Stars and Other Objects That Orbit

Multiple Choice

Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

A) all these faster-moving objects must be escaping from the gravity of the Milky Way and will soon be lost to our Galaxy
B) each of the faster-moving outer objects must be the result of a supernova explosion (giving them extra speed)
C) it is the Sun that is moving too slowly because of a collision billions of years ago; the outer objects are really moving at the appropriate speed for their distance from the center
D) there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there
E) no one can come up with any explanation for this puzzling observation