Galaxy clusters are commonly analyzed under the assumption that the intracluster plasma is approximately hydrostatic within the dominant cluster acceleration field, such that the observed pressure gradient traces the acceleration required for support (Sarazin 1988; Voit 2005). This assumption underlies many cluster-based mass measurements used in cosmological studies (Allen et al. 2011) and plays a central role in the interpretation of systems such as the Bullet Cluster (Clowe et al. 2006). In this work we test a narrower question directly using deprojected X-ray thermodynamic profiles of relaxed galaxy clusters derived from Chandra observations (Vikhlinin et al. 2006): does the observed intracluster plasma structure itself trace the dominant acceleration field? For Abell 2029 and Abell 1795 we compute the acceleration required to support the observed plasma pressure gradient and compare it with a gas-based reference acceleration derived from the observed intracluster plasma distribution under standard Newtonian assumptions. This comparison is used only as a diagnostic baseline and is not intended as a reconstruction of the full cluster acceleration budget. In both clusters the required acceleration exceeds the gas-based reference acceleration by one to two orders of magnitude across nearly the entire radial range. This discrepancy persists after conservative smoothing of the pressure profiles and after Monte Carlo propagation of the reported density and pressure uncertainties. These results indicate that the observed intracluster plasma does not trace the dominant acceleration field even in dynamically relaxed systems. The analysis relies only on observed X-ray thermodynamic profiles and does not assume any particular theory of gravity.
Julie Fragoules (Sat,) studied this question.