Year: 2026
Type: article
Abstract: Einstein’s General Relativity (GR), which has been precisely tested on galaxy and solar system scales, is still poorly constrained in extremely weak gravitational fields (with dimensionless Newtonian potentials of Φ ∼ 10 −8 ). In this Letter, we propose a new method to probe such a weak-field regime of gravity and measure the spatial curvature generated per unit mass. Specifically, binary microlensing events provide a laboratory to measure the parameterized post-Newtonian (PPN) parameter ( γ ), by combining the lensing mass ( M lens GR ) inferred from microlensing with the dynamical mass ( M dyn ) determined from interferometric astrometry. Astrometric tracking of binary lenses was previously hindered by their faintness and minuscule angular separations (typically a few milliarcseconds). This limitation has been alleviated by the deployment of GRAVITY+, which pushes the instrument’s sensitivity and astrometric precision to unprecedented heights. Based on astrometric simulations of the binary microlensing event ASASSN-22av, we directly estimate γ at the precision of ∼23%. Such testing of GR in the extremely weak-field regime can be further improved to a much higher precision (∼3%), based on more binary microlensing events with precise determination of the dynamical/lens mass.
Institution: Beijing Normal University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Awards: G3004611528, G8702593729
OpenAlex ID: W7207704244