The mass of the presently observable matter in a typical rich cluster of galaxies appears to be approximately what fraction of the mass required to hold the cluster together by gravity?
A) 10%
B) 100%, or the entire galaxy
C) about 1%
D) 90%

Question

Quizplus · Accepted Answer

The mass of the observable matter in a typical rich cluster of galaxies is only about 10% of the mass required to hold the cluster together by gravity. This discrepancy is evidence for the existence of dark matter, which does not emit light or radiation that we can currently detect.

The Mass of the Presently Observable Matter in a Typical