An international team led by researchers from The Open University and the University of Bern have directly imaged a remarkable four new brown dwarfs thanks to a new innovative search method.
Brown dwarfs are mysterious astronomical objects straddling the line between stars and planets and are essential to our understanding of both stellar and planetary populations. Yet in almost three decades of searches only 40 could be imaged around stars, until now.
Researchers led by Dr Mariangela Bonavita, Lecturer in Astrophysics at the OU, and Dr Clémence Fontanive from the Center for Space and Habitability (CSH) and the NCCR PlanetS at the University of Bern, directly imaged four new brown dwarfs.
Essential to understanding stars and giant planets
Brown dwarfs fill the gap between the heaviest planets and the lightest stars, with a mix of stellar and planetary characteristics. The researchers reported their findings in a study just published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS). It’s the first time multiple new systems with wide brown dwarf companions have been announced at the same time.
Due to their hybrid nature, brown dwarfs are essential to our understanding of both stars and giant planets. As they orbit a parent star from sufficiently far away they are particularly valuable as they can be directly photographed – unlike those too close to their star as they are hidden by its brightness.
This provides scientists with a unique opportunity to study the details of the cold, planet-like atmospheres of brown dwarf companions.
Innovative search method
“Wide-orbit brown dwarf companions are rare to start with and detecting them directly poses huge technical challenges since the host stars completely blind our telescopes,” says Dr Bonavita.
Most surveys conducted so far have been blindly targeting random stars from young clusters. Dr Fontanive explains: “An alternative approach to increase the number of detections is to only observe stars that show indications of an additional object in their system.” For example, the way a star moves under the gravitational tug of a companion can be an indicator of the existence of that companion, whether it is a star, a planet or something in between.
“We developed the COPAINS tool which predicts the types of companions that could be responsible for observed anomalies in stellar motions,” Dr Fontanive continues. Applying this tool the research team carefully selected 25 nearby stars that seemed promising for the direct detection of hidden, low-mass companions based on data from the Gaia spacecraft of the European Space Agency (ESA).
Using the SPHERE planet-finder at the Very Large Telescope in Chile to observe these stars, they successfully detected ten new companions, including five low-mass stars, a white dwarf (a dense stellar remnant), and a remarkable four new brown dwarfs, with orbits ranging from that of Jupiter to beyond that of Pluto.
Major boost in detection rate
“These findings significantly advance the number of known brown dwarfs orbiting stars from large distances, with a major boost in detection rate compared to any previous imaging survey,” Dr Bonavita explains.
While this approach is mostly limited to signatures from brown dwarf and stellar companions, future phases of the Gaia mission will push these methods to lower masses and allow for the discovery of new giant exoplanets. Dr Fontanive adds: “On top of having so many new discoveries in one go, our programme also demonstrates the power of these search strategies.”
Dr Bonavita said: “This result was only possible because we believed that, when combining space and ground-based 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.”
Publication details:
- Bonavita, C. Fontanive, R. Gratton, K. Mužić, S. Desidera, D. Mesa, B. Biller, A. Scholz, A. Sozzetti, V. Squicciarini: Results from The COPAINS Pilot Survey: four new BDs and a high companion detection rate for accelerating stars, Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 4, July 2022, Pages 5588–5605,
https://academic.oup.com/mnras/article/513/4/5588/6583003
