Which one of these statements about clusters of galaxies is true?
A) The observed mass of the galaxies of the cluster is many thousands of times too small to hold the cluster together.
B) The observed mass of the galaxies of the cluster is about 10 times larger than the amount needed to hold the cluster together.
C) The observed mass of the galaxies in the cluster is about 10 times too small to hold the cluster together.
D) The observed mass of the galaxies of the cluster is almost exactly equal to the mass needed to hold the cluster together.

Question

Quizplus · Accepted Answer

The observed mass of galaxies in a cluster, based on visible matter, is significantly less than what would be needed to hold the cluster together gravitationally. This discrepancy suggests the presence of a significant amount of dark matter, which does not emit light but exerts gravitational force.

Which One of These Statements About Clusters of Galaxies Is