Is there any direct evidence for dark matter—WIMP or Super—WIMP based? The Bullet Cluster may have provided an answer. This is a pair of galaxy clusters that have collided. The collision had little effect on the stars; they passed quietly by each other. However, huge clouds of interstellar gas rammed into one another at 6 million mph, heat up to 100 million degrees celsius and fired out X-rays—(the red areas in the photo at left). It is the blue areas that are the mystery; these were detected in 2006 because of the gravitational lensing of the background stars. Despite the enormous gravitational mass, there is no interaction with anything else happening in the collision—this is very probably dark matter: unreactive particles oblivious to the firestorm around them.