The Acceleration Scale, Modified Newtonian Dynamics, and Sterile Neutrinos

TL;DR

This paper discusses the acceleration scale in galaxies, the MOND theory as an alternative to dark matter, and how sterile neutrinos might reconcile observations across different cosmic scales.

Contribution

It explores a combined model of MOND with sterile neutrinos to explain astrophysical phenomena from galaxy dynamics to cosmic microwave background.

Findings

MOND explains galaxy rotation curves without dark matter.

Sterile neutrinos help reconcile MOND with galaxy cluster observations.

The combined model fits multiple astrophysical data sets.

Abstract

General Relativity is able to describe the dynamics of galaxies and larger cosmic structures only if most of the matter in the Universe is dark, namely it does not emit any electromagnetic radiation. Intriguingly, on the scale of galaxies, there is strong observational evidence that the presence of dark matter appears to be necessary only when the gravitational field inferred from the distribution of the luminous matter falls below an acceleration of the order of 10^(-10) m/s^2. In the standard model, which combines Newtonian gravity with dark matter, the origin of this acceleration scale is challenging and remains unsolved. On the contrary, the full set of observations can be neatly described, and were partly predicted, by a modification of Newtonian dynamics, dubbed MOND, that does not resort to the existence of dark matter. On the scale of galaxy clusters and beyond, however, MOND is not as successful as on the scale of galaxies, and the existence of some dark matter appears unavoidable. A model combining MOND with hot dark matter made of sterile neutrinos seems to be able to describe most of the astrophysical phenomenology, from the power spectrum of the cosmic microwave background anisotropies to the dynamics of dwarf galaxies. Whether there exists a yet unknown covariant theory that contains General Relativity and Newtonian gravity in the weak field limit, and MOND as the ultra-weak field limit is still an open question.