Testing general relativity by micro-arcsecond global astrometry

Abstract

The global astrometric observations of a GAIA-like satellite were modeled within the PPN formulation of Post- Newtonian gravitation. An extensive experimental campaign based on realistic end-to-end simulations was conducted to estab- lish the sensitivity of global astrometry to the PPN parameter γ, which measures the amount of space curvature produced by unit rest mass. The results show that, with just a few thousands of relatively bright, photometrically stable, and astrometrically well behaved single stars, among the ∼10 9 objects that will be observed by GAIA, γ can be estimated after 1 year of continuous observations with an accuracy of ∼10 −5 at the 3σ level. Extrapolation to the full 5-year mission of these results based on the scaling properties of the adjustment procedure utilized suggests that the accuracy of � 2 × 10 −7 ,a t the same 3σ level, can be reached with ∼10 6 single stars, again chosen as the most astrometrically stable among the millions available in the magnitude range V = 12−13. These accuracies compare quite favorably with recent findings of scalar-tensor cosmological models, which predict for γ a present-time deviation, |1 − γ|, from the General Relativity value between 10 −5 and 10 −7 .