In this unit, you are reading about galaxy clusters, in which dark matter once again plays a role. Be sure to read over the Galaxy Clusters lesson before responding to the discussion question. What do you think of the state of the dark matter mystery? Will relativity remove dark matter from galaxy clusters in the same way it may have removed it from the Milky Way? If not, what do you think is the most promising candidate for dark matter? This is a good topic for you to do a little outside reading on - it's a big topic in research, and new information is coming in all the time. If you include a relevant and well-referenced article or video link, I will give you extra credit/extra discussion points on this posting. Note: such a reference is meant to supplement your discussion, not replace it! And Wikipedia doesn't count!