Why is a galaxy cluster like an uncooked cake?

OK, so I've been a bit lax on this blog, but as promised, more updates! (I've been busy with work and dancing, what can I say!). So, why is a galaxy cluster (a what?!) like an uncooked cake.

Well, let's start with a brief introduction of what a galaxy cluster actually is. (Cliche alert!) A galaxy cluster is basically one of the largest gravitationally bound structures in the Universe. About 3,000,000 light years from side to side -- that is to say it takes light 3,000,000 years to get from one side to another (it takes 8 minutes for light to travel from the Sun to the Earth, and 100,000 years for light to travel from one side of the Milky Way to the other), and made up of dark matter, galaxies and gas that's so hot (we're talking 10,000,000 degrees Celsius sort of hot!), that it emits X-rays rather than say visible light. So that's what a galaxy cluster is. Why is it like an uncooked cake (with raisins in it) then?

OK, well, its like this:

Dark matter = Cake tin
Galaxies = Raisins
Hot X-ray Gas = Batter

Your cake tin determines the shape of your cake, right? When you bake your cake, you don't end up with bits of cake tin in your cake -- the tin and the cake don't really interact with each other. You drop your cake, your cake tin retains its shape (more or less). Dark matter in a galaxy cluster is like that. It determines the shape/size of the cluster, it doesn't interact with the galaxies or the hot gas, and after a collision, it keeps its shape, rather like what we see in the Bullet Cluster (we're imaginative with names ;) )

Your raisins just kind of sit there suspended in your cake batter, right? If you apply enough force to them, the raisins will move, but otherwise, they'll basically sit there. Galaxies are the same. Yeah, they move, because they have gravity (from the dark matter) acting on them, but its not really significant.

Now for your cake batter. It flows to conform to the shape of your cake tin, holds your raisins, if your raisins move, it shows the tracks of how the raisins moved, and if you drop your uncooked cake, your batter will fly everywhere. The hot gas is basically the same. It takes on the shape (if undisturbed) provided by the dark matter, traces the motion of the galaxies, traces anything the galaxies do, and if your cluster bumps into another one, the hot gas goes flying everywhere (see the Bullet Cluster above).

And that, ladies and gents, is why a galaxy cluster is like an uncooked cake. :)