# Testing the gravitational redshift with Galileo satellites

## TL;DR

This study tests the gravitational redshift predicted by general relativity using data from Galileo satellites with eccentric and circular orbits, achieving a more precise measurement than previous experiments.

## Contribution

The paper presents a novel analysis of Galileo satellite data to test gravitational redshift, improving measurement accuracy and demonstrating the robustness of the method with different orbit types.

## Key findings

- Measured deviation from general relativity at ( +0.19 ± 2.48 )×10^{-5} for eccentric satellites.
- Achieved a 5.6 times improvement over previous best tests.
- Confirmed the robustness of the analysis method with circular satellites.

## Abstract

We present the results of the analysis of the GREAT (Galileo gravitational Redshift test with Eccentric sATellites) experiment from SYRTE (Observatoire de Paris), funded by the European Space Agency. An elliptic orbit induces a periodic modulation of the fractional frequency difference between a ground clock and the satellite clock, while the good stability of Galileo clocks allows to test this periodic modulation to a high level of accuracy. Galileo satellites GSAT0201 and GSAT0202, with their large eccentricity and on-board H-maser clocks, are perfect candidates to perform this test. By analyzing 1008 days of eccentric Galileo satellites data we measure the fractional deviation of the gravitational redshift from the prediction by general relativity to be $(+0.19 \pm 2.48)\times10^{-5}$ at 1 sigma, improving the best previous test by Gravity Probe A by a factor~5.6. Moreover, we apply the exact same analysis to two almost circular Galileo satellites, in order to show the robustness of the method. By analyzing 899 days of circular Galileo satellites data we measure the fractional deviation of the gravitational redshift from the prediction by general relativity to be $(+0.29 \pm 2.00)\times10^{-2}$ at 1 sigma.