Question: What was the first cluster you saw?

Monique Henson answered on 9 Nov 2015:

I’ve never actually seen a galaxy cluster with my own eyes. It sounds strange doesn’t it – I study them for a living, but I’ve never seen one. In fact, I don’t even use telescopes for my research. Instead, I work with computer models of galaxy clusters. Computer models are a really important part of modern astronomy because they allow us to test our ideas about how the Universe works. Essentially we take all of the knowledge we have about the Universe and use it to develop a set of rules for how we think it works (e.g. a rule for how gravity pulls things together). We then use this to write a computer program that makes a model Universe. If the model Universe ends up looking like the one we see in the sky, then it suggests some of our ideas are right. If it looks really different then we have to go back and adapt our ideas.

You can see some great examples of these kind of computer models here: http://www.illustris-project.org/media/