Hubble telescope finds exoplanet orbiting binary star system

For the first time, researchers have confirmed the existence of a three-body system, using the NASA Hubble Space Telescope to locate a planet orbiting two stars in a system located 8,000 light-years away towards the center of the galaxy, officials announced on Thursday.

Using the telescope and a technique called gravitational microlensing (in which the gravity of a star in the foreground bends and amplifies the light of a background star that momentarily aligns with it), astronomers were able to confirm the existence of the planet and the stars around which it orbits in OGLE-2007-BLG-349, a system located in the Scorpius constellation.

The objects were initially discovered by an international consortium in 2007, and the researchers have determined that the planet orbits around the stars at a distance of approximately 300 million miles, or roughly the same distance between the sun and our asteroid belt.

It completes one orbit around both stars about once every seven years, and the stars themselves are about 7 million miles apart or 14 times the diameter of the moon’s orbit around the Earth, the astronomers explained. A paper detailing the team’s findings has been submitted to and accepted by The Astronomical Journal, a publication of the American Astronomical Society (AAS).

Discovery demonstrates effectiveness of microlensing as planet-hunting tool

The researchers first discovered one of the stars and the planet nine years ago using observations from ground-based telescopes, but additional analysis revealed a third object which could not be identified. As lead author David Bennett of the NASA Goddard Space Flight Center in Maryland explained, there were two different, equally plausible scenarios early on.

“The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star,”  Bennett said. He and his colleagues then used Hubble images along with gravitational microlensing to determine that the light from the foreground lens system was much too faint to have been from a single star.

The brightness level, they determined, was consistent with that of a pair of closely-orbiting red dwarf stars, meaning the system they were looking at had to be comprised of two stars and a single planet. Follow-up observations conducted using Hubble’s Wide Field Planetary Camera 2 with the benefit of a nearly perfect alignment confirmed this discovery, as the lensing magnified the light so much that it “allowed us to see the signal of the two stars,” Bennett said.

Their research has successfully demonstrated that microlensing can detect planets orbiting double-star systems, the authors noted, suggesting that Hubble and its successors may be a powerful tool in the ongoing hunt for new and potentially habitable exoplanets.

“This discovery suggests we need to rethink our observing strategy when it comes to stellar binary-lensing events,” study co-author Yiannis Tsapras from the Astronomisches Recheninstitut (Astronomical Calculation Institute) in Heidelberg, Germany, explained in a statement. “This is an exciting new discovery for microlensing.”

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Image credit: NASA, ESA, and G. Bacon (STScI)

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