Gravitational Redshift for Wide Binaries in Gaia eDR3

TL;DR

This paper discusses how gravitational redshift differences in wide binary stars, observed in Gaia eDR3 data, can be mistaken for deviations from Newtonian gravity, highlighting the importance of accounting for relativistic effects.

Contribution

It identifies gravitational redshift as a dominant factor in wide binary kinematics and clarifies its misinterpretation as modified gravity signals in Gaia data.

Findings

Gravitational redshift differences are significant in wide binaries above 0.01 pc.

Misinterpretation of redshift effects can lead to false claims of modified gravity.

The paper emphasizes the need to consider relativistic effects in binary star analyses.

Abstract

The Doppler effect is commonly used to infer the velocity difference between stars based on the relative shifts in the rest-frame wavelengths of their spectral features. In wide binaries, the difference in gravitational redshift from the surfaces of the constituent stars with distinct compactness dominates at separations above 0.01 pc. I suggest that this effect became apparent for wide pairs in the Gaia eDR3 catalogue but incorrectly interpreted as a possible modification of Newtonian gravity in the internal kinematics of very wide binaries.