Acknowledgements

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory. We thank the technical, administrative, and scientific staff of the participating institutes and the observatory for their extraordinary support during the development, installation, commissioning, and operation of GRAVITY. The instrument relies strongly on the VLTI infrastructure, and we want to especially express thanks for its timely upgrade and continued improvement for GRAVITY and the Second Generation instruments.

[COMMENT: I have combined all received acknowledgements in 3 GROUPS and put them together in "This research was supported by ... , has received funding from ... , and was supported in parts by ... .]

This research was supported by Paris Observatory, by CNRS/INSU, by the Programme National Cosmologie et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES, by the Programme National GRAM of CNRS/INSU with INP and IN2P3, co-funded by CNES and by the Programme National Hautes Energies (PNHE) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES, has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement 730890 (OPTICON), from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 743029), from the Irish Research Council (IRC), grant GOIPG/2016/769 and SFI grant 13/ERC/12907, from the Humboldt Foundation Fellowship and the ESO Fellowship programes, from the European Research Council under the European Union’s Horizon 2020 research and innovation programme under grants agreement Nos. 2016–ADG–74302 (EASY), 2015-StG-677117 (SFH), 694513, and 742095 (SPIDI), and was supported in parts by the German Federal Ministry of Education and Research (BMBF) under the grants Verbundforschung #05A08PK1, #05A11PK2, #05A14PKA and #05A17PKA, by Fundação para a Ciência e a Tecnologia, Portugal, with grants reference UID/FIS/00099/2013, SFRH/BSAB/142940/2018 (P.G.) and PD/BD/113481/2015 (M.F., in the framework of the Doctoral Programme IDPASC Portugal), by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship, from the Direction Scientifique Générale of Onera and by a Grant from Science Foundation Ireland under Grant number 18/SIRG/5597.