Structural Persistence of the Lensing-Defined Gravitational Acceleration Field Through Cluster Merger Stages

Dissociative galaxy cluster mergers provide a unique observational environment in which the spatial relationship between intracluster plasma, galaxies, and the lensing-defined gravitational acceleration field can be directly examined. In these systems the collisional intracluster plasma is slowed and displaced by hydrodynamic interactions while the collisionless galaxy population continues along the merger trajectory, allowing the geometry of the lensing-defined gravitational acceleration field to be probed independently of the dominant baryonic gas component. We examine three well-studied mergers—the Bullet Cluster (1E 0657-56), MACS J0025.4-1222, and DLSCL J0916.2+2951, the Musket Ball Cluster—which span different dynamical stages of the merger process. In every case the lensing-defined field remains aligned with the galaxy distribution while the intracluster plasma is substantially displaced. The same separation hierarchy, with plasma–lensing offsets much larger than galaxy–lensing offsets, recurs across early-, intermediate-, and late-stage mergers. This geometry is consistent with a collisionless dark-matter component, but the observations alone do not uniquely determine the physical origin of the lensing-defined field; they instead define an empirical geometric constraint that any viable model of cluster dynamics must satisfy.