Milky Way Dynamics Favor Dark Matter over Modified Gravity Models

TL;DR

This study uses multiple high-precision observations of the Milky Way to test gravity models, finding strong evidence against modified gravity theories and supporting dark matter models.

Contribution

It provides a novel, independent test that decisively disfavors MOND and STVG, favoring dark matter explanations for galactic dynamics.

Findings

Modified gravity models cannot reproduce both radial and vertical observations simultaneously.

MOND is disfavored at more than 13 sigma; STVG at more than 4 sigma.

Dark matter halo models are consistent with all observed data.

Abstract

Modified gravity theories such as Modified Newtonian Dynamics (MOND) and Scalar-Tensor-Vector Gravity (STVG) have been proposed as alternatives to dark matter, but decisive tests have been hindered by degeneracies between baryonic structure and gravitational laws. Here we break this degeneracy using independent, high-precision constraints: the Milky Way radial rotation curve, vertical phase-space spirals from Gaia, and a broken-exponential stellar disk. A joint reconstruction of the radial and vertical gravitational fields reveals a structural inconsistency in modified gravity -- no model can simultaneously reproduce both observations. Our results strongly disfavor MOND at $>13\sigma$ and STVG at $>4\sigma$. In contrast, dark matter halo models naturally explain the observations, providing a self-consistent test of gravity on galactic scales.