Testing general relativity by micro-arcsecond global astrometry

¹ Istituto di Fisica “G. Galilei”, Via Marzolo 8, 35100 Padova, Italy
² Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova
³ Centro per gli Studi e le Attività Spaziali “G. Colombo” (CISAS), Padova
⁴ INAF, Osservatorio Astronomico di Torino, 10025 Pino Torinese TO, Italy

Corresponding author: M. G. Lattanzi, lattanzi@to.astro.it

Received: 24 October 2002
Accepted: 27 November 2002

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 establish 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 ~10⁹ 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 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 , at the same level, can be reached with ~ 10⁶ single stars, again chosen as the most astrometrically stable among the millions available in the magnitude range . These accuracies compare quite favorably with recent findings of scalar-tensor cosmological models, which predict for γ a present-time deviation, , from the General Relativity value between 10^-5 and  10^-7 .