We can measure the motions of the galaxies in a galaxy cluster to determine the mass of the entire cluster, similar to the way we measure stellar motions within an elliptical galaxy to determine the g...We can measure the motions of the galaxies in a galaxy cluster to determine the mass of the entire cluster, similar to the way we measure stellar motions within an elliptical galaxy to determine the galaxy’s mass. Astronomers have found that the mass of the luminous, or light-emitting, matter from the galaxies in the cluster and from the gas in between the galaxies makes up only about 10% of the cluster’s total mass.
