Perspectives on binary stars and exoplanets with Gaia DR4 and VLTI/GRAVITY

Gaia DR4 will be different from previous releases thanks to the publication of individual astrometric epochs for all targets. Previously released parameters were limited to average values over the Gaia observing window (three years for the DR3). Epoch measurements will enable deeper analyses taking into account the complexity of individual objects through a refined modelling of their sky trajectories. Two main cases can be distinguished: binaries or multiple stars for which each component is measured separately by Gaia (resolved systems) and binary targets for which the companions are very faint and/or spatially unresolved. A large number of resolved systems is present in existing Gaia releases. Anomalies in the motion of single targets provide unique hints on dark and/or very low mass orbiting companions. I will present the example of the Gaia BH3 black hole and exoplanets. I will conclude on how to prepare for the interpretation of Gaia DR4 data.