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Image of Luhman 16AB
Courtesy NASA / JPL / Gemini Observatory / AURA / NSF
Pasadena, CA— Astronomers, including Carnegie’s Yuri Beletsky, took
precise measurements of the closest pair of failed stars to the Sun,
which suggest that the system harbors a third, planetary-mass object.The
research is published as a letter to the editor in Astronomy &
Astrophysics available online at http://arxiv.org/abs/1312.1303.
Failed stars are known as brown dwarfs and have a mass below 8% of
the mass of the Sun—not massive enough to burn hydrogen in their
centers. This particular system, Luhman 16AB, was discovered earlier
this year and is only 6.6 light-years away.
After the discovery announcement, several teams of astronomers,
including the one with Beletsky, used a variety of telescopes to
characterize the neighbouring couple.
After two-months of observations and extensive data analysis,
Beletsky’s team, led by Henri Boffin of the European Southern
Observatory (ESO), found that both objects 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,” explained Beletsky.
The team used the FORS2 instrument on ESO’s Very Large Telescope at
Paranal to image the brown dwarf couple in the best possible conditions,
every 5 or 6 days over the period April 14, to June 22, 2013. Because
of the instrument enabled the observers to make very precise
measurements, the scientists were already able to detect tiny
displacements of the two objects in their orbit during only this the
two-month period.
The astronomers were able to measure the positions of the two brown
dwarfs with ten times better accuracy than before and thereby detect
even small perturbations of their orbit.
“We have been able to measure the positions of these two objects with
a precision of a few milli-arcseconds,” said Boffin. “That is like a
person in Paris being able to measure the position of someone in New
York with a precision of 10 centimetres.”
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 two months and a year.
“Further observations are required to confirm the existence of a
planet,” concludes Boffin. “But it may well turn out that the closest
brown dwarf binary system to the Sun turns out to be a triple system!”
The team is composed of Henri Boffin, Kora Muzic, Valentin Ivanov, Andrea Mehner, Jean-Philippe Berger, Julien Girard, and Dimitri Mawet (ESO, Chile), Dimitri Pourbaix (Université Libre de Bruxelles, Belgium), Rudy Kurtev (Universidad de Valparaiso, Chile), and Yuri Beletsky (Carnegie Observatories at Las Campanas Observatory, Chile).
