"For about half of the planet's orbit, which lasts 550 Earth-years, three stars are visible in the sky; the fainter two are always much closer together, and change in apparent separation from the brightest star throughout the year," added Ph.D. student Kevin Wagner, also of the University of Arizona and discoverer of HD 131399Ab.
On an extra-special note, the direct imaging of HD 131399Ab is the first exoplanetary discovery for the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument that is attached to the ESO's Very Large Telescope (VLT) located in Chile.
Now it has been found, more observations are needed to understand the exoplanet's orbital trajectory.
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The exoplanet's wide orbit around HD 131399A takes it a third of the way to the orbit of the HD 131399BC binary. The constant gravitational turbulence caused by this 3-star configuration should be enough to knock the exoplanet off-kilter. And yet there it is, apparently stable and merrily going about its strange orbit.
"If the planet was further away from the most massive star in the system, it would be kicked out of the system," said Apai. "Our computer simulations have shown that this type of orbit can be stable, but if you change things around just a little bit, it can become unstable very quickly."
This discovery serves to remind us that multi-star planetary systems may be a common occurrence in our galaxy; just because there's more stars orbiting one another, it doesn't necessarily mean the gravitational dynamics will make planetary formation and orbital stability impossible -- it simply adds a whole new layer of exoplanetary possibilities.
This research has been published in the journal Science.