No Dark Core Required in Abell 520: A Comprehensive Refutation Based on Geometric and Statistical Analysis

The claim of a “dark core” in galaxy cluster Abell 520—a concentration of dark matter spatially separated from galaxies—has been presented as a challenge to collisional dark matter models. Using a comprehensive suite of 15 independent robustness tests (R1–R15), geometric analysis, and rigorous model comparison via information criteria (AIC, BIC, LOOIC), we demonstrate that no dark core is required to explain the observational data. Our analysis, conducted entirely without dark matter (DM) sector terms under the framework MMA-DMF, reveals that weak lensing (WL) mass peaks form an elongated ridge-like structure significantly offset from the X-ray centroid. A simple two-parameter geometric model (NormalRidge) decisively outperforms the dark-core-at-centroid hypothesis (DarkCore@X) with ΔBIC ≈ 1.55×10³, ΔAIC ≈ 1.55×10³, representing Jeffreys’ “decisive” evidence against the dark core interpretation. All geometric tests confirm that the X-ray peak lies outside the convex hull of WL peaks, with minimum separations >19.6″ (>47 kpc), and strong axial alignment (p ≈ 5.2×10⁻⁴). The mass-to-light ratios at 150 kpc remain consistent with normal baryonic cores across multiple photometric backgrounds and k-corrections. By Occam’s razor—both in requiring no additional entity and no DM sector—the standard interpretation of distributed mass with a normal baryonic core is preferred. We conclude that the “dark core” phenomenon in A520 is an artifact of incomplete error propagation and insufficient model comparison in previous analyses.