Astronomers have detected what they think may be an exoplanet circling a brown dwarf pair called Luhman 16AB, the third-closest star system to the Sun.
Luhman 16AB, also known as WISE 1049-5319, was discovered earlier this year by Prof Kevin Luhman of Penn State University and his colleagues.
“The distance to this brown dwarf pair is 6.5 light years – so close that Earth’s television transmissions from 2006 are now arriving there,” Prof Luhman noted.
Luhman 16AB is only slightly farther away than the second-closest star, Barnard’s star, which was discovered 6 light-years from the Sun in 1916.
After the discovery, astronomers around the world used a variety of telescopes to characterize the pair.
After two-months of observations and extensive data analysis, a team led Dr Henri Boffin of the European Southern Observatory found that both brown dwarfs have a mass between 30 and 50 Jupiter masses. By comparison, the Sun has a mass of about 1,000 Jupiter masses.
“The two brown dwarfs are separated by about three times the distance between the Earth and the Sun. Binary brown dwarf systems are gravitationally bound and orbit about each other. Because these two dwarfs have so little mass, they take about 20 years to complete one orbit,” said team member Dr Yuri Beletsky of Carnegie Observatories at Las Campanas Observatory, who is a co-author of the paper published in online in the journal Astronomy & Astrophysics (arXiv.org).
The astronomers used ESO’s Very Large Telescope to image Luhman 16AB in the best possible conditions every 5 or 6 days over the period from April 14 to June 22, 2013. They detected tiny displacements of the brown dwarfs in their orbit during only this the two-month period. They also measured the positions of the objects with 10 times better accuracy than before and thereby detect even small perturbations of their orbit.
The measurements were so fine that the astronomers were able to see some very small deviations from the expected motion of the two brown dwarfs around each other. The fact that the deviations appear correlated is a strong indication that a companion perturbs the motion of one of the two brown dwarfs. This companion is most likely a planetary-mass object, which has an orbital period between 2 months and a year.
Dr Boffin concluded: “further observations are required to confirm the existence of a planet. But it may well turn out that the closest brown dwarf binary system to the Sun turns out to be a triple system!”
Boffin HMJ et al. 2013. Possible astrometric discovery of a substellar companion to the closest binary brown dwarf system WISE J104915.57-531906.1. Astronomy & Astrophysics, published online December 11, 2013; doi: 10.1051/0004-6361/201322975