# Is there a fundamental acceleration scale in galaxies?

## TL;DR

This study revisits the question of whether a universal acceleration scale exists in galaxies, finding that current data do not strongly support MOND's prediction of a fundamental acceleration constant.

## Contribution

The paper applies Bayesian analysis to a large galaxy sample to assess the existence of a universal acceleration scale, challenging previous claims and highlighting the need for more precise data.

## Key findings

- Broad posterior distributions of acceleration scale weaken the case for a universal constant.
- Incompatibility between global fit and marginalized distributions reduces support for MOND.
- More accurate observations are necessary to confirm or refute the fundamental acceleration scale.

## Abstract

Milgrom's modified Newtonian dynamics (MOND) can explain well the mass discrepancy problem in galaxy without invoking dark matter. The MOND theory predicts a universal constant acceleration scale in galaxy, below which the Newtonian dynamics is no longer valid. Recently, Rodrigues et al. analyzed 193 high-quality disk galaxies by using Bayesian inference and they concluded that the probability of existence of a fundamental acceleration scale is essentially 0. In this paper, we use the same method to revisit the same question: Is there a fundamental acceleration scale in galaxies? We fit each galaxy rotation curve of 175 SPARC galaxies with Gaussian priors on galaxy parameters and a variable acceleration scale. After marginalizing over the nuisance parameters, we find that the marginalized posterior distributions of the acceleration scale become broad. The incompatibility between the global best fit and the marginalized posterior distributions of the acceleration scale is greatly reduced. However, there still exists evidence that rejects MOND as a fundamental theory. More accurate observations are needed to exclude or confirm the existence of a fundamental acceleration scale in galaxies.