Dark Matter Exists!!

There is a great post by Sean at Cosmic Variance on the new Dark Matter discovery. The post was slashdotted early Tuesday my time, so I couldn’t get at it until this evening. It’s compulsory reading for everyone.

There are just two important things to note here. Firstly, as pointed out in the article and comments, approximately 90% of the visible mass of the galaxy clusters lies in the intergalactic gas, and only about 10% comes from the galaxies themselves. The gravitational field from the galaxies that remain in the cluster after the collision is negligible. This is not where the gravity is coming from. Secondly the dark matter is only weekly interacting, both with other dark matter and also with the plasma. The Dark Matter in both clusters wouldn’t be slowed down by the collision. You would expect it to end up with the visible center of the clusters, where it would have been before the collision, which is exactly what the results show.

Of course, now we finally know for certain that this stuff exists, the next challenge is to figure out exactly what it is, and to make some of it here on earth. This is one of the most interesting problems in particle physics today, and will be one of the major goals of the Large Hadron Collider and the International Linear Collider.