Which of the following is not a way that astronomers can find how much dark matter there is in cluster of galaxies?

a. Using gravitational lensing effects to make a map of how much mass a cluster of galaxies contains.
b. Observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them.
c. Observing X-rays from the hot gas in the cluster, and using the amount of x-ray radiation to estimate the mass of the cluster.
d. Measuring how much slower galaxies in a rich cluster or supercluster are moving than the Hubble Law would predict.
e. Measuring the speeds with which the galaxies are moving around, to estimate the mass of the cluster needed to keep them from moving away.

b. Observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them.

Explanation:

The universe is thought to be made up of 85% dark matters. Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it doesn't absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect. This means that option b is wrong since radio wave is an electromagnetic wave. Dark matter is a form of matter that makes up about a quarter of the total mass–energy density of the universe. Dark matter was theorized due a variety of astrophysical observations and gravitational effects that cannot be explained by accepted theories of gravity unless there were more matter in the universe than can be seen.