An artist’s impression of the exoplanet 2M1510 (AB) b’s unusual orbit around a pair of brown dwarfs
ESO/L. Calçada
In a first, a pair of unusual stars has been revealed to have an equally unusual companion – an exoplanet that orbits them perpendicularly.
Astronomers may think they know what is normal for stars and planets, “but the universe is very diverse”, says Amaury Triaud at the University of Birmingham, UK. He and his colleagues unexpectedly found evidence of the rare configuration while analysing data collected by the Very Large Telescope in Chile.
The two stars are brown dwarfs, which means they are both small and very dim because they can’t sustain nuclear fusion and are often referred to as failed stars or substellar objects. They follow orbits such that they keep eclipsing each other when viewed from Earth. Researchers have only observed one eclipsing brown dwarf binary before.
When Triaud and his colleagues carefully analysed the new binary system to determine the masses of the stars and how they move, they found an unexpectedly strange signal in the data. Ultimately, the only physical scenario that could explain it was one involving a planet-sized object orbiting the two stars, tracing out an ellipse perpendicular to the stars’ orbits.
Triaud says that perpendicular orbits aren’t completely unheard of, but he and his colleagues never expected to see one in this context. “Brown dwarfs are rare. Pairs of brown dwarfs are rare. Eclipsing pairs of brown dwarfs are even rarer and faint, so it’s difficult to make measurements,” he says. “That’s where the surprise was, that in a system which was far from being ideal and rare in itself we have this configuration.”
Twenty years ago, such configurations were considered science fiction, but now they have become science fact, says Katherine Blundell at the University of Oxford. “This is a really beautiful result,” she says. The details of the two stars’ precessing orbits make a strong case that this “harmonograph in the sky” is real. Studying how they eclipse each other will make it possible to pin down more details about the motion of this peculiar threesome going forward, says Blundell.
While the researchers want to learn more about the exoplanet, named 2M1510 (AB) b, they can draw comparisons with the fictional Tatooine in Star Wars, a desert world that orbited two suns. However 2M1510 (AB) b’s two suns would be dimmer, basking its surface in something similar to a double dose of moonlight.
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