Astronomers have used the NASA/ESA Hubble Space Telescope to track the two components of Luhman 16AB, the third closest system to the Solar System.
This series of dots with varying distances between them shows the slow dance of two members of the brown-dwarf binary system Luhman 16AB. The image is a stack of 12 images made over the course of three years with Hubble. Image credit: NASA / ESA / Hubble / L. Bedin et al.
Luhman 16AB, also known as WISE J104915.57-531906.1, is a pair of brown dwarfs located in the southern constellation Vela, approximately 6.5 light-years away from Earth.
It is the third closest stellar system to our Sun, after the triple star system Alpha Centauri and Barnard’s Star.
Another peculiarity of this pair is that, after Alpha Centauri AB, it is the nearest known binary system to the Sun.
Despite its proximity, Luhman 16AB was only discovered in 2013 by Penn State University astronomer Prof. Kevin Luhman.
The two brown dwarfs that make up the system, Luhman 16A (primary) and Luhman 16B (secondary), orbit each other at a distance of only three times the distance between the Earth and the Sun.
Luhman 16A is of spectral type L7.5 and Luhman 16B of type T0.5; both at effective temperatures of about 1,880 degrees Fahrenheit (1,027 degrees Celsius, or 1,300 degrees Kelvin).
The estimated age of this system is between 100 million years and 3 billion years.
Both brown dwarfs are known variables, with Luhman 16B more strongly variable than Luhman 16A. The variability likely originates from patchy clouds.
Using high-precision astrometry from Hubble, an international team of astronomers led by the INAF- Astronomical Observatory of Padova tracked the two components of the Luhman 16AB system as they moved both across the sky and around each other.
The researchers were not only interested in the waltz of the two brown dwarfs, but were also searching for a third, invisible companion.
Earlier observations with ESO’s Very Large Telescope indicated the presence of an exoplanet in the system.
The team wanted to verify this claim by analyzing the movement of the brown dwarfs in great detail over a long period of time, but the Hubble data showed that the two dwarfs are indeed dancing alone, unperturbed by a planetary companion.
“Although our data seem to be inconsistent with recent ground-based astrometric measurements, we exclude the presence of third bodies down to Neptune masses and periods longer than a year,” the authors said.
The results will be published in the Monthly Notices of the Royal Astronomical Society, but have been published on arXiv.org ahead of time.
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L.R. Bedin et al. 2017. Hubble Space Telescope astrometry of the closest brown dwarf binary system — I. Overview and improved orbit. MNRAS, accepted for publication; arXiv: 1706.00657
