Testing general relativity using millimeter wavelength radio interferometry of Sgr A*

Abstract

General relativity, though widely accepted in the weak-field limit, is difficult to test in the strong-field regime. Millimeter wavelength VLBI offers a unique opportunity to resolve the black hole structure on event-horizon scales. The ability of millimeter wavelength VLBI observations of Sgr A* to constrain black hole parameters such as mass, spin, and deviation from general relativity was considered. Realistic simulations of Sgr A* were performed using the MAPS software. Image reconstructions were made using MACIM and image-based parameter extraction using the Hough transform was considered. Non-imaging techniques using least-squares fitting of a simple ring and gaussian model to VLBI amplitudes and closure phases were considered. The Hough transform is not able to place strong constraints on black hole parameters. Least-squares fitting techniques indicate possible sensitivity to deviations from general relativity and prove able to extract the photon ring radius to within 5-7% of the expected value. It is concluded that VLBI observations of Sgr A* represent a promising opportunity for testing general relativity in the strong-field regime.