Author ORCID Identifier
Document Type
Article
Publication Date
11-20-2020
Abstract
The strong equivalence principle (SEP) distinguishes general relativity (GR) from other viable theories of gravity. The SEP demands that the internal dynamics of a self-gravitating system under freefall in an external gravitational field should not depend on the external field strength. We test the SEP by investigating the external field effect (EFE) in Milgromian dynamics (MOND), proposed as an alternative to dark matter in interpreting galactic kinematics. We report a detection of this EFE using galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample together with estimates of the large-scale external gravitational field from an all-sky galaxy catalog. Our detection is threefold: (1) the EFE is individually detected at 8σ to 11σ in "golden"galaxies subjected to exceptionally strong external fields, while it is not detected in exceptionally isolated galaxies, (2) the EFE is statistically detected at more than 4σ from a blind test of 153 SPARC rotating galaxies, giving a mean value of the external field consistent with an independent estimate from the galaxies' environments, and (3) we detect a systematic downward trend in the weak gravity part of the radial acceleration relation at the right acceleration predicted by the EFE of the MOND modified gravity. Tidal effects from neighboring galaxies in the Λ cold dark matter (CDM) context are not strong enough to explain these phenomena. They are not predicted by existing ΛCDM models of galaxy formation and evolution, adding a new small-scale challenge to the ΛCDM paradigm. Our results point to a breakdown of the SEP, supporting modified gravity theories beyond GR.
Corrections were made to this article on 2021 January 12. The image quality of Figure 2 was improved (see additional files).
Keywords
non-standard theories of gravity (1118), disk galaxies (391), gravitation (661), modified Newtonian dynamics (1069)
Language
English
Publication Title
Astrophysical Journal
Grant
693024 NASA ADAP 80NSSC19k0570 NSF PHY-1911909
Rights
© 2020. The Author(s). Published by the American Astronomical Society. This is an Open Access work distributed under the terms of the Creative Commons Attribution Licence (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Kyu-Hyun Chae et al. Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies. 2020 ApJ 904 51
Manuscript Version
Final Publisher Version
Comments
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