UC astrophysicist takes part in discovery of exoplanet orbiting two stars at the same time
This is the first time that strong evidence has been found for one of these 'polar planets' orbiting two stars at once.
An international group of scientists has discovered a planet orbiting two stars simultaneously at a perfect 90-degree angle. This is the first time that strong evidence has been found for one of these 'polar planets' orbiting two stars at the same time, a discovery made using the European Southern Observatory's (ESO) Very Large Telescope (VLT).
In recent years, several planets have been discovered orbiting two stars, known as circumbinary planets. Typically, these planets orbit in the same plane as the host stars themselves (coplanar orbits).
However, there had already been hints that planets could also exist in perpendicular, or polar, orbits around binary stars. In theory, such orbits are stable, and planet-forming disks have been detected in polar orbits around binary stars. But until now, there had been no clear evidence that polar planets actually exist.
"I am quite excited to be involved in finding credible evidence for the existence of this configuration," says Thomas Baycroft, a PhD student at the University of Birmingham, UK, who led the study published in the journal Science Advances.
The exoplanet, called 2M1510 (AB) b, orbits a binary system of young brown dwarfs - objects larger than gas giant planets but considered "failed stars" because they are too small to sustain hydrogen fusion into helium. The two brown dwarfs eclipse each other when observed from Earth, forming what scientists refer to as an “eclipsing binary”.
This is quite rare. Not only is it only the second known eclipsing binary brown dwarf system, but experts have now discovered that it hosts the first exoplanet ever found to follow a trajectory perpendicular to the orbits of its two host stars.
" Usually, polar orbits tend to increase the orbital eccentricity and often lead to collisions between objects. However, when the orbit is around a binary star system, as in this case, it can remain dynamically stable," explains Alexandre Correia, professor at the Department of Physics of the Faculty of Sciences and Technology of the University of Coimbra (FCTUC) and researcher at the Centre for Physics of the University of Coimbra (CFisUC). "What is really surprising is how this planet evolved into such an orbit, since most planet formation theories predict only coplanar orbits," adds the co-author of the study.
The scientists discovered the planet while refining the orbital and physical parameters of the two brown dwarfs, using observations made with the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile. This pair of brown dwarfs, known as 2M1510, was first detected in 2018 by Amaury Triaud and other researchers using SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars), another facility at Paranal.
The team observed that the orbits of the two stars in 2M1510 were being pushed in an unusual way, which led them to conclude that an exoplanet with this peculiar orbital angle was present. "We explored all possible scenarios, and the only one consistent with the data corresponds to the existence of a planet in a polar orbit around this binary system," the researchers report.
"This discovery was quite unexpected, because our observations were not collected to look for a planet or an orbital configuration of this kind. So, it was indeed a big surprise," they conclude.
The scientific paper "Evidence for a polar circumbinary exoplanet orbiting a pair of eclipsing brown dwarfs" is available here.