We propose the bigravitational interference induced Lagrange surface and low-density vacuum region theory, predicting that Lagrange surfaces in binary gravitational systems host low-density vacuum regions (K < 1) caused by bigravitational interference. Photons traversing these regions exhibit frequency shifts (redshift entering, blueshift exiting) and anomalous refraction distinct from standard gravitational lensing. For extreme mass-ratio systems (e.g., stellar-mass black hole with companion), the low-density region assumes an asymmetric "flying saucer" shape elongated toward the primary mass, with the Lagrange surface centered at the Lagrange point. This produces characteristic asymmetric Einstein arcs with redshift gradients—a unique signature distinguishable from General Relativity predictions. We introduce the universal constant α relating vacuum density to gravitational contrast, propose its physical interpretation as a new fundamental property of spacetime akin to the speed of light, and outline observational tests using black hole-companion-quasar lensing systems for the prediction of α.
Fei Li (Mon,) studied this question.