Dynamical Friction Constraints on the Dark Matter Hypothesis Across Astronomical Scales

TL;DR

This paper examines how dynamical friction constraints challenge the dark matter hypothesis by showing that in several astronomical systems, the predicted orbital decay timescales are inconsistent with their observed lifetimes, thus questioning the dark matter explanation.

Contribution

It provides a comprehensive review of dynamical friction constraints across various astronomical systems, highlighting cases where dark matter halos are implausible based on orbital decay timescales.

Findings

Dynamical friction timescales often shorter than system lifetimes when assuming dark matter halos.

Several systems, including dwarf galaxies and the Magellanic Clouds, challenge the dark matter hypothesis.

Orbital decay constraints exclude certain dark matter models for these systems.

Abstract

Dynamical friction implies a consistency check on any system where dark matter particles are hypothesised to explain orbital dynamics requiring more mass under Newtonian gravity than is directly detectable. Introducing the assumption of a dominant dark matter halo will also imply a decay timescale for the orbits in question. A self-consistency constraint hence arises, such that the resulting orbital decay timescales must be longer than the lifetimes of the systems in question. While such constraints are often trivially passed, the combined dependencies of dynamical friction timescales on the mass and orbital radius of the orbital tracer and on the density and velocity dispersion of the assumed dark matter particles leads to the existence of a number of astronomical systems where such a consistency test is failed. Here, we review cases from stars in ultrafaint dwarf galaxies, galactic bars, satellite galaxies, and, particularly, the multi-period mutual orbits of the Magellanic Clouds, as recently inferred from the star formation histories of these two galaxies, as well as the nearby M81 group of galaxies, where introducing enough dark matter to explain observed kinematics leads to dynamical friction orbital decay timescales shorter than the lifetimes of the systems in question. Taken together, these observations exclude dark matter halos made of particles as plausible explanations for the observed kinematics of these systems.