Discovery of a record number of brown dwarfs

Brown dwarfs are mysterious astronomical objects that bridge the heaviest planets and the lightest stars, with a mixture of star and planetary characteristics. Because of this hybrid nature, these confusing 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 photographed directly, as opposed to those that are too close to their star and therefore hidden by its brightness. This gives scientists a unique opportunity to study the details of the cold, planetary atmospheres of brown dwarf comrades.

But despite remarkable efforts in the development of new observation technologies and imaging techniques, direct detection of star-associated brown dwarfs has remained quite rare, with only about forty systems depicted 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 depicted four new brown dwarfs, which they report in a study just published. the newspaper Royal Astronomical Society MNRAS monthly announcements. This is the first time that several new systems with brown dwarf companions across wide orbital separations have been announced at the same time.

Innovative research method

“Widely orbiting brown dwarf companions are rare at first, and detecting them directly poses enormous technical challenges as host stars completely blind our telescopes,” says Mariangela Bonavita. Most studies so far have blindly targeted random stars from young clusters. “An alternative approach to increasing the number of detections is to only observe stars that show traces 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.

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

Large increase in detection speed

“These results dramatically increase the number of known brown dwarfs orbiting stars at great distances, with a significant increase in detection speed compared to any previous image study,” says Mariangela Bonavita. While this approach is currently mainly limited to the signatures of brown dwarfs and stellar companions, future phases of the Gaia mission will push these methods toward 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 strength of these research strategies.”

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

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