Halfway between the planet and the star, new brown dwarfs have been spotted in the Milky Way

Brown dwarfs are larger than planets but smaller than stars, and are difficult to detect due to their low luminosity. They are even less noticeable when you are near a star a thousand times brighter.

Many of them could be observed because they “wandered around on their own, like isolated objects, so we were not dazzled by the star,” explained Sylvester Laqueur, a researcher at the National Center for Scientific Research and one of the authors of the study published this week in the journal Astronomy and Astrophysics.

But for the first time, brown dwarfs have been found orbiting close to their host stars, at distances equivalent to those that separate the Earth from the Sun.

Eight “candidates”

Astronomers started from the latest catalog of the European space probe Gaia, which maps the stars in the Milky Way, along with their locations. Some presented “a very special orbital motion, which led us to believe that a brown dwarf could orbit,” the astrophysicist says.

Eight “candidates” are selected to be targeted from thousands of star systems. Thanks to these indications, the gravitational instrument of the Very Large Telescope (VLTI) of the European Southern Observatory (ESO) in Chile was set to “take a look at the expected location,” explains Karine Babusio, a researcher at the University of Grenoble Alpes. Also author of the study.

Acting as a magnifying glass, the interferometer precisely measured objects previously identified by Gaia. Thus, scientists were able to analyze their luminosity and mass, and conclude the existence of brown dwarfs for five of the eight candidates. These “hidden companions” of stars, located less than 200 light-years from Earth, have a mass between 60 and 80 times the mass of Jupiter.

“Failed Stars”

This discovery will allow us to better understand what brown dwarfs are, which are celestial objects that can be compared to “aborted stars.” Scientists are particularly interested in knowing whether these objects are “born like stars, by a compressed gas cloud, or like planets, on the edges of an accretion disk around a star,” says Sylvester Laqueur.

Unlike a star, a brown dwarf does not burn hydrogen in its core. It is therefore much less luminous (a thousand times less bright in the case of this study), but it still emits a luminous flux that planets do not have.