Gas DM Offsets

In galaxy clusters that have undergone recent mergers — most dramatically in the Bullet Cluster and similar systems — the X-ray emitting intracluster gas and the gravitational mass traced by weak lensing become spatially offset. The gas, experiencing ram pressure during the merger, is slowed and displaced from the dark matter halos, which pass through each other essentially collisionlessly. These offsets between the gas centroid and the total mass centroid have been used as powerful evidence for dark matter and to set limits on dark matter self-interaction cross sections. However, the statistical distribution of gas-mass offsets across large cluster samples shows a tail of large offsets that is more extended than ΛCDM simulations predict, and certain merging clusters exhibit asymmetric gas distributions and non-trivial velocity structures that complicate the simple gas-versus-collisionless-matter interpretation.

Successive Collision Theory provides a unified framework for understanding gas-mass offsets that does not invoke dark matter particles, instead explaining both the offset itself and its statistical distribution through gravitational superposition and angular momentum inheritance. In SCT, the 'dark matter' analog is the gravitational superposition of overlapping nested comoving frames — a distributed, smooth gravitational contribution that is genuinely collisionless and non-dissipative in the same way that dark matter particles are assumed to be. During a cluster merger, the superposition contribution tracks the stellar and compact-object mass (which is also collisionless) rather than the gas, naturally producing a spatial offset between the X-ray gas and the total effective gravitational mass. The Bullet Cluster offset is therefore explained by the same mechanism in SCT as in ΛCDM, but without requiring particles: the effective dark mass is the superposition contribution from the frame hierarchy, which moves with the collisionless component.

The excess tail of large offsets in the statistical distribution of cluster mergers is explained in SCT through the angular momentum inheritance mechanism. Clusters with higher inherited angular momentum have gas distributions that are more extended and have shallower central concentration relative to the collisionless component, because the centrifugal barrier from inherited angular momentum supports the gas against gravitational compression more effectively than it affects the frame superposition contribution, which has no angular momentum of its own. During a merger, higher-angular-momentum clusters therefore produce larger gas-mass offsets at equivalent merger velocities, extending the offset distribution toward larger values. SCT predicts the magnitude of the gas-mass offset tail should correlate with the cluster spin parameter inferred from galaxy velocity fields — a cross-correlation testable with upcoming combined weak lensing, X-ray, and spectroscopic cluster surveys.