Special and General Relativistic Effects in Galactic Rotation Curves

TL;DR

This paper explores how relativistic effects in galaxy rotation curves can distinguish between dark matter and modified gravity theories, proposing observable tests for these effects.

Contribution

It calculates the expected relativistic Doppler and gravitational shifts in galaxy models within general metric theories of gravity, proposing observational strategies.

Findings

Relativistic effects are potentially detectable in galaxy rotation curves.

Observable quantities can measure special- and general-relativistic effects independently.

Combining data from many galaxies enhances detection prospects.

Abstract

The observed flat rotation curves of galaxies require either the presence of dark matter in Newtonian gravitational potentials or a significant modification to the theory of gravity at galactic scales. Detecting relativistic Doppler shifts and gravitational effects in the rotation curves offers a tool for distinguishing between predictions of gravity theories that modify the inertia of particles and those that modify the field equations. These higher-order effects also allow us in principle, to test whether dark matter particles obey the equivalence principle. We calculate here the magnitudes of the relativistic Doppler and gravitational shifts expected in realistic models of galaxies in a general metric theory of gravity. We identify a number of observable quantities that measure independently the special- and general-relativistic effects in each galaxy and suggest that both effects might be detected in a statistical sense by combining appropriately the rotation curves of a large number of galaxies.