We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.
Stacy McGaugh, Federico Lelli, Jim Schombert, "The Radial Acceleration Relation in Rotationally Supported Galaxies
" (September 19, 2016).
The dynamics of galaxies of almost every kind can be fully explained by the distribution of ordinary matter in those galaxies.
As a result, one of two things must be true. Either General Relativity is not an accurate description of weak gravitational fields and need to be modified in some fashion to reflect this reality, or there is some mechanism by which the distribution of dark matter in a galaxy and the distribution of ordinary matter in a galaxy are rigidly intertwined.
Nothing axiomatic about dark matter theories explains why there is such a tight relationship between the distribution of ordinary matter and the distribution of dark matter in a galaxy, although a wide variety of dark matter theories approximately reproduce observed galactic behavior. But, this could simply reflect our ignorance of an emergent property of what is naively a pretty simple dark matter model.
In this paper McGaugh, a leading physicists advocating for a gravity modification solution to dark matter phenomena in other publications, doesn't resolve that question.
An article discussing the paper is here
, and the main fault in the article is the assumption that this research is new or groundbreaking, when it really simply sums up conclusions that have been widely discussed ever since Dr. Milgrom published his first paper on the topic