We compare recent results from X-ray, strong lensing, weak lensing, and optical observations with numerical simulations of the merging galaxy cluster 1E 0657–56. X-ray observations reveal a bullet-like subcluster with a prominent bow shock, which gives an estimate for the merger velocity of 4700 km s−1, while lensing results show that the positions of the total mass peaks are consistent with the centroids of the collisionless galaxies (and inconsistent with the X-ray brightness peaks). Previous studies, based on older observational data sets, have placed upper limits on the self-interaction cross section of dark matter per unit mass, σ/m, using simplified analytic techniques. In this work, we take advantage of new, higher quality observational data sets by running full N-body simulations of 1E 0657–56 that include the effects of self-interacting dark matter, and comparing the results with observations. Furthermore, the recent data allow for a new independent method of constraining σ/m, based on the nonobservation of an offset between the bullet subcluster mass peak and galaxy centroid. This new method places an upper limit (68% confidence) of σ/m < 1.25 cm2 g−1. If we make the assumption that the subcluster and the main cluster had equal mass-to-light ratios prior to the merger, we derive our most stringent constraint of σ/m < 0.7 cm2 g−1, which comes from the consistency of the subcluster's observed mass-to-light ratio with the main cluster's, and with the universal cluster value, ruling out the possibility of a large fraction of dark matter particles being scattered away due to collisions. Our limit is a slight improvement over the previous result from analytic estimates, and rules out most of the 0.5-5 cm2 g−1 range invoked to explain inconsistencies between the standard collisionless cold dark matter model and observations.

Constraints on the Self‐Interaction Cross Section of Dark Matter from Numerical Simulations of the Merging Galaxy Cluster 1E 0657−56