Jackpot

Thanks to GRAVITY’s uniquely sharp and sensitive eye, the team caught the light signal of all eight predicted companions, seven of which were previously unknown. Three of the companions are very small and faint stars, while the other five are brown dwarfs. These are celestial objects in between planets and stars: more massive than the heaviest of planets but lighter and fainter than the lightest of stars.

One of the brown dwarfs spotted in this study orbits its host star at the same distance as Earth from the Sun. This is the first time a brown dwarf so close to its host star could be directly captured¬.

“We have demonstrated that it is possible to capture an image of a faint companion, even when it orbits very close to its bright host,” explains Thomas. “This achievement highlights the remarkable synergy between Gaia and GRAVITY. Only Gaia can identify such tight systems hosting a star and a ‘hidden’ companion, and then GRAVITY can take over to image the smaller and fainter object with unprecedented accuracy.”

In an earlier study, astronomers used Gaia data and a different ground-based observatory to capture the image of a giant gas exoplanet. This planet orbits its host star at about 17 times the distance of Earth from the Sun, tracing an angle in the sky considerably wider than the typical separation of the companions imaged by GRAVITY in this new result.

The small companions inferred from Gaia observations typically lie at tiny separation angles of a few dozen milliarcseconds, which is about the size of a one-Euro coin viewed from 100 km distance.

“In our observations, Gaia data act as a kind of signpost,” continues Thomas. “The part of the sky that we can see with GRAVITY is very small, so we need to know where to look. Gaia’s unparalleled precise measurements of the movements and positions of stars are essential to point our instrument to the right direction in the sky”.