Suppose stars at 1000 ly from the center of a galaxy and those at 2000 ly from the center of the galaxy both revolve at the same speed.How would the mass within 2000 ly of the center of the galaxy compare to the mass within 1000 ly of the center of the galaxy?

Question

Quizplus · Accepted Answer

According to Kepler's third law, if stars at different distances from the center of a galaxy revolve at the same speed, the mass within the larger radius (2000 ly) must be greater. Specifically, the mass within 2000 ly would be twice as great as the mass within 1000 ly, assuming a roughly spherical distribution of mass.

Suppose Stars at 1000 Ly from the Center of a Galaxy