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Exoplanet with two ‘suns’ is even more unique than Tatooine
This is an artist’s impression of the exoplanet 2M1510 (AB) b’s unusual orbit around its host stars, a pair of brown dwarfs. The newly discovered planet has a polar orbit, which is perpendicular to the plane in which the two stars are travelling. Polar planets around single stars had been found before, as well as polar discs of gas and dust capable of forming planets around binary stars. But thanks to ESO’s Very Large Telescope (VLT) this is the first time we have strong evidence that such a planet actually exists in a polar orbit around two stars. The two brown dwarfs appear as a single source in the sky, but astronomers know there are two of them because they periodically eclipse each other. Using the UVES spectrograph on the VLT they measured their orbital speed, and noticed that their orbits change over time. After carefully ruling out other explanations, they concluded that the gravitational tug of a planet in a polar orbit was the only way to explain the motion of the brown dwarfs. Credit: ESO / L. Calçada Get the Popular Science daily newsletter💡 The image of Luke Skywalker gazing wistfully across the desert of Tatooine while a pair of “suns” set on the horizon is among of the most famous scenes in pop culture. When Star Warscircumbinary planet in 1993. Still, only 15 examples have been located to date—but researchers now have strong evidence suggesting another should be added to the list. What’s more, it’s one of the most unique binary systems ever observed. The evidence was published on April 16 in the journal Science Advances. When you imagine a stellar system and its orbiting planets, chances are it largely resembles our own solar system. In actuality, our cosmic neighborhood is actually a comparatively rare sight. Of the nearly 6,000 exoplanets documented so far, more than 75 percent exist in stellar orbits radically different from our own. One of the rarest variations is a binary system, in which the path of a planet revolves around two stars. However, the exoplanet 2M1510’s binary system includes a slightly different pairing: brown dwarfs. Brown dwarfs are cosmic oddballs—while too large to classify as planets, they’re also too small to truly meet the definition of a star. But at 13 to 80 times the mass of Jupiter, they exhibit more than enough gravitational pull to draw objects into orbit. 2M1510 is one such object. However,  in this case, there are two brown dwarfs involved here. The result, according to researchers, is an exoplanet that “eccentrically orbits” the pair. To confirm the rarely detected space oddity, astronomers utilized radial velocity calculations to examine data previously collected by NASA’s Kepler space telescope, the Transiting Exoplanet Survey Satellite (TESS), as well as the European Space Southern Observatory’s Very Large Telescope (VLT). This combination of tools and analyses allowed astronomers to bypass  a longstanding physic issue called the three-body problem. This conundrum makes it extremely difficult to assess gravitational behavior between three objects interacting in space. The resulting evidence strongly suggests 2M1510 orbits at a 90-degree polar angle, and moves perpendicular to the dwarfs’ orbits in a never-before-seen way. Adding to its uniqueness, the brown dwarfs are eclipsing, meaning that one of them is always partially obscured when seen from Earth. This also makes it only the second eclipsing brown dwarf binary system ever documented. “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,” Amaury Triaud, a study co-author and professor at the University of Birmingham, said in a statement. According to an accompanying Science Advances “Focus” feature, the system also “provides strong, if indirect, evidence for the existence of one of the most exotic types of exoplanetary systems yet found.”But as rare a find as it is, it’s possible that 2M1510 once had an even more surreal skyscape. That’s because they aren’t only two brown dwarfs in the cosmic neighborhood. A third, more distant brown dwarf is located at the system’s periphery. According to the study’s authors, this hints at a time when a trio of brown dwarfs occupied the system’s center before the gravitational forces pushed it out of the unit. At this point, however, only time will tell if a three-star planet makes it into a Star Wars film.
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