The non-gravitational interactions of dark matter in colliding galaxy clusters

Understand

Collisions between galaxy clusters provide a test of the non-gravitational forces acting on dark matter.

• Dark matter's lack of deceleration in the `bullet cluster collision' constrained its self-interaction cross-section \sigma_DM/m < 1.25cm2/g (68% confidence limit) for long-ranged forces.
• Using the Chandra and Hubble Space Telescopes we have now observed 72 collisions, including both `major' and `minor' mergers.
• Combining these measurements statistically, we detect the existence of dark mass at 7.6\sigma significance.