Testing the Weak Equivalence Principle near black holes

Today we have quite stringent constraints on possible violations of the Weak Equivalence Principle from the comparison of the acceleration of test-bodies of different composition in Earth's gravitational field. In this talk, I show how we can test the Weak Equivalence Principle in the strong gravitational field of black holes by studying the reflection features of their accretion disks. Constraints on a possible violation of the Weak Equivalence Principle by massive particles and X-ray photons are inferred from a NuSTAR observation of the black hole binary EXO 1846-031.