A severe challenge to the MOND phenomenology in our Galaxy

TL;DR

This paper analytically examines the MOND framework in our Galaxy and finds that recent observations of declining rotation curves strongly challenge MOND's validity as a universal galactic theory.

Contribution

It provides the first analytical derivation of the galactic rotation curve gradient in MOND and tests its phenomenology against recent Galactic data.

Findings

Declining rotation curve in the outer Galaxy challenges MOND at over 5 sigma

Analytical derivation of rotation curve gradient in MOND framework

Supports the view that MOND is not a fundamental or universal galactic theory

Abstract

Modified Newtonian Dynamics (MOND) is one of the most popular alternative theories of dark matter to explain the missing mass problem in galaxies. Although it remains controversial regarding MOND as a fundamental theory, MOND phenomenology has been shown to widely apply in different galaxies, which gives challenges to the standard $\Lambda$ cold dark matter model. In this article, we derive analytically the galactic rotation curve gradient in the MOND framework and present a rigorous analysis to examine the MOND phenomenology in our Galaxy. By assuming a benchmark baryonic disk density profile and two popular families of MOND interpolating functions, we show for the first time that the recent discovery of the declining Galactic rotation curve in the outer region ($R \approx 17-23$ kpc) can almost rule out the MOND phenomenology at more than $5\sigma$. This strongly supports some of the previous studies claiming that MOND is neither a fundamental theory nor a universal description of galactic properties.