How Does Gravitational Lensing Tell Us About the Mass of a Galaxy

question 27

Multiple Choice

How does gravitational lensing tell us about the mass of a galaxy cluster?

• A) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.
• B) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law.
• C) The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster.
• D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.