2025ApJ...981..195M

Modified Newtonian dynamics (MOND) was originally proposed to model galaxy rotation curves without dark matter. However, MOND presents difficulties in explaining the radial acceleration relation observed in galaxy clusters, and moreover, it does not completely eliminate the need for dark matter, since it requires using nonluminous particles (e.g., cold molecular gas or dust, or neutrinos) to explain the observed hydrostatic equilibrium of the hot gas. Hyperconical modified gravity (HMG) offers a relativistic framework that recovers the success of MOND in galaxy rotation curves as a natural particular case, and it could potentially reconcile the previously described discrepancies without invoking any type of dark matter. This paper analyzes the performance of the HMG model for hydrostatic equilibrium in 12 XMM Cluster Outskirts Project galaxy clusters, with a special focus on 5 objects with available complete stellar mass information: A1795, A2029, A2142, A2319, and A644. Specifically, we used high-resolution X-ray data with which gas density and mass profiles were previously derived to constrain modified gravity models. Our results show that the hydrostatic equilibrium of analyzed cluster gas is more naturally adjusted to the HMG model beyond 1 Mpc, reducing the need to fit parameters, but further research is required to expand to more spatial scales.