Testing the equivalence principle via the shadow of black holes

Sheng Feng Yan, Chunlong Li, Lingqin Xue, Xin Ren, Yi Fu Cai, Damien A. Easson, Ye Fei Yuan, Hongsheng Zhao

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


We study the equivalence principle, regarded as the cornerstone of general relativity, by analyzing the deformation observable of black hole shadows. Such deformation can arise from new physics and may be expressed as a phenomenological violation of the equivalence principle. Specifically, we assume that there is an additional background vector field that couples to the photons around the supermassive black hole. This type of coupling yields impact on the way the system depends on initial conditions and affects the black hole shadow at different wavelengths by a different amount, and therefore observations of the shadow in different wavelengths could constrain such couplings. This can be tested by future multiband observations. Adopting a specific form of the vector field, we obtain constraints on model parameters from Event Horizon Telescope observations and measurements of gas/stellar orbits.

Original languageEnglish (US)
Article number023164
JournalPhysical Review Research
Issue number2
StatePublished - May 2020

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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