I want to thank everyone for their great interest in my last post on dark matter! I got an awful lot of questions about what I mean by dark matter being “collisionless,” and in particular, about this picture:
This is two galaxy clusters that have collided recently. The pink shows the X-ray emissions, which comes from the normal matter in the clusters colliding and heating up. The blue shows the mass, and where it is, which I contend needs to be mostly dark matter.
Well, many of you are skeptical, and rightfully so. So I’ve decided to set you straight, by showing you a visual simulation (that I scavenged) of a pair of colliding galaxy clusters. They contain both collisionless dark matter (in blue) and normal, splat-able matter (in pink). Let’s take a look at what happens when we run these into each other (use the control bar and double-click on the image to start/stop the animation):
These theories are called non-local theories of gravity, and you would need a different theory of gravity for every different configuration of colliding galaxy clusters. So you’d need one theory for the bullet cluster (above), another one for Abell 520:
Another one for MACS J0025:
And another one for all the clusters that have not yet collided!
Or, you need dark matter. I’m not going to state that this proves anything, but it, in combination with all the other things that dark matter explains, convinces me. And I hope it helps clear things up for you!