Astronomers have discovered a planet that orbits at a 90-degree angle around a rare pair of strange stars – a real-life 'twist' on the fictional twin suns of Star Wars hero Luke Skywalker's home planet of Tatooine.
The exoplanet, named 2M1510 (AB) b, orbits a pair of young brown dwarfs — objects bigger than gas-giant planets but too small to be proper stars. Only the second pair of eclipsing brown dwarfs known – this is the first exoplanet found on a right-angled path to the orbit of its two host stars.
An international team of researchers led by the University of Birmingham, made the surprise discovery using the European Southern Observatory's Very Large Telescope (VLT). The brown dwarfs produce eclipses of one another, as seen from Earth, making them part of an 'eclipsing binary'.
Publishing their discovery today (16 Apr) in Science Advances, the researchers note that this is the first time such strong evidence for a 'polar planet' orbiting a stellar pair is collected.
Thomas Baycroft, a PhD student at the University of Birmingham who led the study commented: "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."
The team found this planet while refining the orbital and physical parameters of the two brown dwarfs by collecting observations with the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on the VLT at Paranal Observatory, Chile.
The astronomers observed the orbital path of the two stars in 2M1510 being pushed and pulled in unusual ways, leading them to infer the existence of an exoplanet with its strange orbital angle.
The pair of brown dwarfs, known as 2M1510, were detected in 2018 by Professor Amaury Triaud and others with the Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) that the University of Birmingham partially owns.
Co-author Professor Triaud, from the University of Birmingham, commented: "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.
"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."
The discovery was made possible thanks to pioneering data analysis developed at Birmingham by Dr Lalitha Sairam (now at the University of Cambridge), who developed new methods that improved precision by a factor of 30.
Dr Sairam explains: "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."
