title: The nongravitational interactions of dark matter in colliding galaxy clusters.
abstract: Collisions between galaxy clusters provide a test of the nongravitational forces acting on dark matter. Dark matter's lack of deceleration in the "bullet cluster" collision constrained its self-interaction cross section σ(DM)/m < 1.25 square centimeters per gram (cm(2)/g) [68% confidence limit (CL)] (σ(DM), self-interaction cross section; m, unit mass of dark matter) 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 7.6σ significance. The position of the dark mass has remained closely aligned within 5.8 ± 8.2 kiloparsecs of associated stars, implying a self-interaction cross section σ(DM)/m < 0.47 cm(2)/g (95% CL) and disfavoring some proposed extensions to the standard model.
authors: Laboratoire d'Astrophysique, École Polytechnique Fédérale de Lausanne, Observatoire de Sauverny, 1290 Versoix, Switzerland. Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK. david.harvey@epfl.ch.
authors: David
authors: D
authors: Harvey
authors: Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK.
authors: Richard
authors: R
authors: Massey
authors: Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK.
authors: Thomas
authors: T
authors: Kitching
authors: Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK.
authors: Andy
authors: A
authors: Taylor
authors: Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK.
authors: Eric
authors: E
authors: Tittley