In 2018, astronomers discovered a pair of brown dwarf stars orbiting each other in a rare system known as an eclipsing binary. Further observations show that this binary, named 2M1510, is even more unique than previously thought.
The researchers report the discovery of an exoplanet, named 2M1510(AB)b, that orbits its parent star at a 90-degree angle – the so-called polar orbit – with respect to the plane of the brown dwarfs’ orbit. The discovery, made with the European Southern Observatory’s (ESO) Very Large Telescope (VLT), is the first time scientists have documented strong evidence for the existence of a “polar planet” orbiting a star pair, as detailed in a study published Wednesday in the journal Science Advances.
“A planet orbiting not just a double, but a double brown dwarf, and in a polar orbit, is pretty incredible and exciting,” said Amaury Trio, co-author of the study and an astronomer at the University of Birmingham in the UK, in a statement to ESO.
According to the study, to date, astronomers have discovered 16 circumbinary planets – exoplanets orbiting two stars. The orbits of these planets are roughly in the same plane as the orbits of the double stars that orbit each other. Until the recent discovery, scientists had only theorized the existence of such a system with a circumbinary planet in a perpendicular orbit – the so-called polar orbit – based on evidence such as the discovery of perpendicular planet-forming disks around pairs of stars.
“I am particularly pleased to have been involved in identifying strong evidence for this configuration,” said Thomas Bancroft, a PhD student in astronomy and astrophysics at the University of Birmingham and lead author of the study.
In addition to the exoplanet’s polar orbit, the pair of brown dwarfs themselves are extremely rare. They form an eclipsing double, meaning that their orbital trajectories cause them to eclipse each other as we see them from Earth. 2M1510 consists of only the second pair of brown dwarfs known to science.
While studying these two brown dwarfs, Triod, Bancroft and their colleagues noticed that their orbital trajectories are strangely “pushing and pulling”. This suggests the presence of an exoplanet in an unusual orbital plane, whose gravity, according to the researchers, is likely to affect the binary pair, the statement said.
“We have considered all possible scenarios, and the only one that is consistent with the data is if the planet is in a polar orbit around this binary,” Bancroft added.
“The discovery… was unexpected in the sense that our observations were not designed to look for such a planet or orbital configuration. So it’s a big surprise,” Trio summarized. “Overall, I think it shows us as astronomers, as well as the general public, what is possible in the fascinating Universe that we inhabit.”
