Question

By measuring the rotation curves of galaxies beyond the Milky Way, astronomers have determined that dark matter exists in individual galaxies. Because dark matter is a part of galaxies, astronomers need to determine if dark matter also exists between galaxies.

Considering a galaxy cluster as a gravitationally bound system, astronomers estimate the total mass of the cluster by measuring the movements of the individual galaxies relative to one another. The total mass of a cluster can then be compared to the estimated mass of the observable matter: individual galaxies and hot, intracluster gas.

For example, by measuring the motions of galaxies in a particular cluster, the mass of the cluster is determined to be 800 MMW (where MMW is a unit of mass equal to the mass of the Milky Way Galaxy). When the mass of the visible matter is added up, the individual galaxies have a total mass of 40 MMW, and the hot intracluster gas between galaxies has a total mass of 80 MMW. What conclusions can be drawn about the nature of the galaxy cluster's mass?

Check all that apply.

A) Most of the cluster's mass is accounted for by the hot intracluster gas.
B) Most of the cluster's mass cannot be seen as visible matter.
C) Most of the cluster's mass is accounted for by the individual galaxies.
D) The mass of the dark matter accounts for more of the gravitational force within the cluster than does the mass of the visible matter.
E) The mass of the visible matter accounts for more of the gravitational force within the cluster than does the mass of the dark matter.

Answer 1

Most of the galaxy cluster's mass cannot be seen as visible matter and the dark matter within the cluster accounts for more gravitational force than the visible matter. This implies the cluster contains a substantial amount of dark matter which is not detectable by standard luminosity measurements.

Step-by-step explanation:

When analyzing the mass of a galaxy cluster, astronomers estimate the total mass by measuring the velocities of galaxies within the cluster. A specific galaxy cluster's mass is determined to be 800 MMW, while the sum of the visible matter accounts for only 120 MMW (40 MMW from galaxies and 80 MMW from intracluster gas). The conclusions drawn from this data are:

• B) Most of the cluster's mass cannot be seen as visible matter.
• D) The mass of the dark matter accounts for more of the gravitational force within the cluster than does the mass of the visible matter.

The mass of the dark matter surpasses the combined mass of the galaxies within the cluster and the hot intracluster gas. This indicates that a significant amount of mass within the galaxy cluster cannot be accounted for by the visible matter alone, and most of the gravitational force is likely due to dark matter. Observations and calculations suggest that dark matter exists between galaxies as well as inside them, playing a crucial role in the dynamics of galaxy clusters.