The host objects, both classified as brown dwarfs, lie in a rare category of substellar binaries that eclipse one another as seen from Earth. Brown dwarfs occupy the mass range between large gas giants and stars but lack sufficient mass to ignite hydrogen fusion. The planetary discovery was made using the European Southern Observatory's Very Large Telescope (VLT) located at Paranal Observatory in Chile.
Led by a team from the University of Birmingham, the international collaboration published their findings in the journal Science Advances. According to the researchers, this configuration demonstrates the existence of a 'polar planet' that orbits perpendicular to the orbital plane of its dual suns.
"I'm particularly excited to be involved in detecting credible evidence that this configuration exists. We had hints that planets on perpendicular orbits around binary stars could exist, but until now we lacked clear evidence of this type of polar planet. We reviewed all possible scenarios, and the only consistent with the data is if a planet is on a polar orbit about this binary," said lead author Thomas Baycroft, a PhD student at the University of Birmingham.
The team uncovered the planet while analyzing high-resolution spectral data from the VLT's UVES instrument to refine the characteristics of the two brown dwarfs. Their observations revealed subtle gravitational interactions in the binary system, pointing to the gravitational influence of an orbiting planet.
The brown dwarf pair, known as 2M1510, was first observed in 2018 as part of the SPECULOOS project (Search for habitable Planets EClipsing ULtra-cOOl Stars), partially funded and operated by the University of Birmingham.
"A planet orbiting not just a binary, but a binary brown dwarf, as well as being on a polar orbit is rather incredible and exciting," said co-author Professor Amaury Triaud. "The discovery was serendipitous, as our observations were not collected to seek such a planet, or orbital configuration. As such, it is a big surprise and shows what is possible in the fascinating universe we inhabit, where a planet can affect the orbits of its two stars, creating a delicate celestial dance."
This breakthrough was enabled by a novel analytical method developed by Dr Lalitha Sairam during her time at Birmingham, now at the University of Cambridge. Her approach significantly enhanced measurement accuracy.
"From variations in velocity of the two brown dwarfs, we can measure their physical and orbital parameters, however being faint, these measurements and therefore their parameters were uncertain. Thanks to that improvement we noticed the orbits of the two brown dwarfs around one another were being delicately affected," explained Dr Sairam.
Research Report:Evidence for a polar circumbinary exoplanet orbiting a pair of eclipsing brown dwarfs
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