Absence of a fundamental acceleration scale in galaxies

TL;DR

This study analyzes 193 galaxies and finds no evidence for a universal acceleration scale, suggesting that the Radial Acceleration Relation's scale is emergent and not fundamental, challenging modified gravity theories like MOND.

Contribution

It provides strong statistical evidence that a universal acceleration scale does not exist across galaxies, refuting theories that treat it as fundamental.

Findings

No universal acceleration scale found (p-value < 10^{-20})

Radial Acceleration Relation is likely emergent, not fundamental

MOND and similar theories are ruled out as fundamental explanations

Abstract

The Radial Acceleration Relation confirms that a nontrivial acceleration scale can be found in the average internal dynamics of galaxies. The existence of such a scale is not obvious as far as the standard cosmological model is concerned, and it has been interpreted as a possible sign of modified gravity. The implications could be profound: it could in principle explain galactic dynamics without large amounts of yet-undetected dark matter and address issues that the standard cosmological model faces at galactic scales. Here, we consider 193 disk galaxies from the SPARC and THINGS databases and, using Bayesian inference, we show that the probability of existence of a fundamental acceleration that is common to all the galaxies is essentially zero: the $p$-value is smaller than $10^{-20}$ or, equivalently, the null hypothesis is rejected at more than 10$\sigma$. We conclude that the acceleration scale unveiled by the Radial Acceleration Relation is of emergent nature, possibly caused by a complex interplay between baryons and dark matter. In particular, the MOND theory, or any other theory that behaves like it at galactic scales, is ruled out as a fundamental theory for galaxies at more than 10$\sigma$.