The Bullet Cluster is not a Cosmological Anomaly

TL;DR

This paper demonstrates through detailed simulations that the Bullet Cluster's observed properties align with the standard Lambda-CDM cosmological model, challenging previous claims of anomalies requiring new physics.

Contribution

The study provides comprehensive, pixel-by-pixel simulations including MHD and cooling, showing the Bullet Cluster's features are consistent with Lambda-CDM, unlike earlier models suggesting anomalies.

Findings

Bullet Cluster's properties match Lambda-CDM predictions

Previous simulations required unrealistically high initial velocities

No need for new physics or modifications to gravity

Abstract

The Bullet Cluster (1E0657-56) merger is of exceptional interest for testing the standard cold-dark-matter plus cosmological constant cosmological model, and for investigating the possible existence of a long- or short-range "fifth-force" in the dark sector and possible need for modifications of general relativity or even of Newtonian gravity. The most recent previous simulations of the Bullet Cluster merger required an initial infall velocity far in excess of what would be expected within the standard cosmological model, at least in the absence of additional forces or modifications to gravity. We have carried out much more detailed simulations, making pixel-by-pixel fits to 2D data-maps of the mass distribution and X-ray emission, allowing for triaxial initial configurations and including MHD and cooling. Here, we compare the initial conditions of the Bullet Cluster merger to those in similar-mass merging clusters in the Horizon cosmological simulation. We conclude that the observed properties of the Bullet Cluster are completely consistent with Lambda-CDM.