GRAVITY - Reaching out to SgrA* with VLTI

International audienceAs one of the 2nd generation of interferometric instruments in VLTI, GRAVITY was in-stalled at the end of 2015 and has been observing the Galactic Center since May 2016. Withthe goal to reach an accuracy of tens of micro arcseconds, it is able to perform the mostprecise astrometric measurement of SgrA* to date. For that purpose, GRAVITY combinesthe light collected (coherently) from of all the 8 m UTs or the four 1.8 m ATs providing in-frared wavefront sensing to control the telescope adaptive optics, two interferometric beamcombiners (one for fringe-tracking and one for the science object), an acquisition cameraand various laser guiding systems for beam stabilization, as well as a dedicated laser metrol-ogy to trace the optical path length differences for narrow angle astrometry. Operating inK band with an active stabilization of the science channel, GRAVITY is able to increasethe typical integration time from a few milliseconds (the typical atmospheric coherencetime) to minutes, which implies a big leap in sensitivity allowing to observe fainter objects(K=19 in science detector) with the power of a 130m baseline interferometer, as it is theclose environment of the supermassive black hole located in the center of our Galaxy