Beyond Dark Matter: Testing Alternative Gravity Theories at Galactic Scales Exploring Modified Newtonian Dynamics MOND vs Dark Matter Using Recent Astrophysical Datasets

Abstract

The lack of a resolution to the tension between the unjustified Newtonian Dynamics (MOND) and the Lambda-Cold Dark Matter (Lambda  CDM) paradigm is one of the most far-reaching unanswered questions in modern astrophysics with direct implications on the nature of gravity and the makeup of the universe itself. This paper gives a multi-scale, systematic comparative analysis of the two frameworks using current state-of-the-art astrophysical data such as the SPARC database of 175 disk galaxies, the LITTLE THINGS dwarf irregular galaxy survey, the ROSAT/XMM-Newton galaxy cluster catalogue of 65 systems, and 22 pressure-supported elliptical galaxies of the ATL Affine-invariant Markov Chain Monte Carlo sampling with strict Bayesian Information Criterion and Bayes factor model comparison between the two frameworks was used to perform rotation curve fitting. The findings demonstrate that a strong and statistically significant scale dependent behavior exists: MOND has a higher explanatory power at galactic scales - in particular low-mass and low-surface-brightness rotationally supported systems - with BIC and Bayes factor differences of greater than 450 and 3.85 to 5.2 respectively in favor of MOND compared to ΛCDM over the dwarf and spiral galaxy populations. In contrast, ΛCDM is clearly favored on the galaxy cluster scales, where MOND underestimates cluster masses by factors of three to five, and the Bayes factor is less than 0.01. The Baryonic Tully-Fisher Relation is replicated by MOND as a parameter-free prediction with astounding accuracy, and cluster observations such as the Bullet Cluster pose MOND with difficulty which cannot be overcome without additional mass components. These results demonstrate that both paradigms in their present formulation cannot give an adequately universal account of gravitational phenomenology on all the astrophysical scales, which prompts the construction of unified theoretical frameworks that do not lose the predictive power of MOND in the Galaxy, but restore in the high-mass environments its dark matter-like behavior.

Keywords: Modified Newtonian Dynamics (MOND), Dark Matter, Lambda-Cold Dark Matter (ΛCDM), Galactic Rotation Curves, SPARC Database, Baryonic Tully-Fisher Relation, Bayesian Model Comparison, Radial Acceleration Relation, Galaxy Clusters, Gravitational Phenomenology, Markov Chain Monte Carlo, Alternative Gravity Theories.