Scientists capture hidden companions of bright stars using advanced techniques

Artist impression of a brown dwarf orbiting close to a bright star. Credit: ESA, CC BY-SA 3.0 IGO or ESA Standard License.

Photographing faint objects near bright stars is incredibly challenging, like trying to snap a picture of a firefly next to a bright streetlight.

However, by combining data from ESA’s Gaia space telescope with ESO’s GRAVITY instrument on Earth, scientists have successfully captured images of dim companions orbiting eight luminous stars.

This breakthrough opens up new possibilities for capturing images of planets orbiting close to their host stars.

Led by Thomas Winterhalder from the European Southern Observatory (ESO), the international team began by searching through Gaia’s catalog, which lists stars suspected to have companions.

Although Gaia cannot directly see these companions, it detects tiny wobbles in the paths of the brighter host stars, indicating the presence of a hidden object.

From Gaia’s catalog, the team selected eight stars to observe with GRAVITY, an advanced near-infrared interferometer at the Very Large Telescope in Chile. GRAVITY combines infrared light from different telescopes to reveal tiny details in faint objects using a technique called interferometry.

The results were published in the journal Astronomy & Astrophysics.

Using GRAVITY’s sharp and sensitive capabilities, the team detected light signals from 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—objects that are more massive than planets but lighter and fainter than stars.

One of these brown dwarfs orbits its host star at the same distance as Earth from the sun, marking the first time a brown dwarf so close to its host star has been 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,” explained Thomas. “This achievement highlights the remarkable synergy between Gaia and GRAVITY. Gaia identifies tight systems hosting a star and a ‘hidden’ companion, and GRAVITY images the smaller and fainter object with unprecedented accuracy.”

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

The small companions identified from Gaia observations are typically very close to their host stars, with separation angles of just a few dozen milliarcseconds—about the size of a one-Euro coin viewed from 100 kilometers away.

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

The combination of Gaia and GRAVITY data allows scientists to “weigh” individual celestial objects separately, distinguishing the mass of the host star from its companion. GRAVITY also measures the contrast between the companion and host star across various infrared wavelengths, helping to estimate the age of the companions.

Surprisingly, two of the brown dwarfs were less luminous than expected for their size and age, possibly indicating they have even smaller companions.

Having demonstrated the power of the Gaia-GRAVITY duo, scientists are now excited to search for potential planetary companions of stars listed in the Gaia catalog.

Johannes Sahlmann, ESA’s Gaia scientist, remarked, “This result breaks new ground in the hunt for planets in our galaxy and promises glimpses of new distant worlds.”