Brown dwarfs are mysterious astronomical objects that bridge the gap between the heaviest planets and the lightest stars, with a mix of stellar and planetary characteristics. Because of this hybrid nature, these puzzling objects are crucial to improving our understanding of giant stars and planets. Brown dwarfs orbiting a sufficiently distant parent star are particularly valuable because they can be directly photographed, unlike those that are too close to their star and are therefore hidden by its luminosity. This provides scientists with a unique opportunity to study the details of the cold, planetary atmospheres of brown dwarf companions.

However, despite remarkable efforts in the development of new observation technologies and image processing techniques, direct detections of star companion brown dwarfs have remained rather rare, with only about forty systems imaged in nearly three decades of research. Researchers led by Mariangela Bonavita of the Open University and Clémence Fontanive of the Center for Space and Habitability (CSH) and NCCR PlanetS at the University of Bern have directly imaged four new brown dwarfs as they report in a study just released. to be published in the newspaper Royal Astronomical Society MNRAS Monthly Notices. This is the first time that multiple new systems with brown dwarf companions across wide orbital separations have been announced at the same time.

Innovative research method

“Broad-orbiting brown dwarf companions are initially rare, and detecting them directly poses enormous technical challenges since host stars completely blind our telescopes,” says Mariangela Bonavita. Most surveys so far have blindly targeted random stars from young clusters. “An alternative approach to increase the number of detections is to observe only stars that show clues of an additional object in their system”, explains Clémence Fontanive. For example, the way a star moves under the gravitational pull of a companion can be an indicator of that companion’s existence, whether it’s a star, a planet, or something in between. both.

“We have developed the COPAINS tool which predicts the types of companions that could be responsible for the anomalies observed in stellar movements”, continues Clémence Fontanive. Applying the BUDDY tool, the research team carefully selected 25 nearby stars that showed promise for the direct detection of low-mass hidden companions based on data from the European Space Agency (ESA) Gaia spacecraft. Then using the Very Large Telescope’s SPHERE planet finder in Chile to observe these stars, they managed to detect ten new companions with orbits ranging from Jupiter to Pluto, including five low-mass stars, a white dwarf ( a dense stellar remnant), and four remarkable new brown dwarfs.

Major increase in detection rate

“These findings dramatically increase the number of known brown dwarfs orbiting stars at great distances, with a major increase in detection rate over any previous imaging survey,” says Mariangela Bonavita. While for the moment this approach is mainly limited to the signatures of brown dwarfs and stellar companions, future phases of the Gaia mission will push these methods towards lower masses and allow the discovery of new giant exoplanets. Clémence Fontanive adds: “In addition to having so many new discoveries at once, our program also demonstrates the power of these research strategies.”

“This result was only possible because we believed that by combining space and ground facilities to directly image exoplanets, the whole is greater than the sum of its parts. We hope this will be the start of a new era of synergy between different instruments and detection methods”, concludes Mariangela Bonavita.

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