At an estimated distance of 130.5 light-years, CWISE J014611.20-050850.0AB has a projected separation of 129 AU (astronomical units), or 129 times the distance between the Sun and the Earth, making it the widest-separation brown dwarf pair found to date.
Brown dwarfs are cool, dim objects that have a size between that of a gas-giant planet and that of a Sun-like star.
Sometimes called failed stars, these objects are too small to sustain hydrogen fusion reactions at their cores, yet they have star-like attributes.
Typically, they have masses between 11-16 Jupiters (approximate mass at which deuterium fusion can be sustained) and 75-80 Jupiters (approximate mass to sustain hydrogen fusion).
While stars are often found in binary systems, brown dwarf binaries are much rarer.
“Because of their small size, brown dwarf binary systems are usually very close together. Finding such a widely separated pair is very exciting,” said study’s first author Emma Softich, an undergraduate student at Arizona State University.
In the study, the researchers inspected images of brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, where companion brown dwarfs may have been overlooked.
In doing so, they discovered CWISE J014611.20-050850.0AB (CWISE J0146-0508AB for short), a wide brown dwarf binary located 130.5 light-years away in the constellation of Cetus.
Based on its significant proper motion, one of the system members, CWISE J0146-0508A, was previously submitted as an object of interest by citizen scientists Nikolaj Stevnbak, Sam Goodman, Melina Thévenot, Dan Caselden, and Frank Kiwy.
The astronomers then used data from the Dark Energy Survey (DES) to confirm that it was indeed a brown dwarf pair.
“Wide, low-mass systems like CWISE J014611.20-050850.0AB are usually disrupted early on in their lifetimes, so the fact that this one has survived until now is pretty remarkable,” said study’s co-author Dr. Adam Schneider, an astronomer with the U.S. Naval Observatory and George Mason University.
To measure the spectral types of CWISE J0146-0508A and CWISE J0146-0508B, the researchers observed both components with the Near-Infrared Echellette Spectrometer (NIRES) located on the Keck II telescope.
They confirmed the brown dwarfs have spectral types L4 and L8, and that they have a projected separation of 129 AU.
“Binary systems are used to calibrate many relations in astronomy, and this newly discovered pair of brown dwarfs will present an important test of brown dwarf formation and evolution models,” said study’s co-author Dr. Jennifer Patience, an astronomer at Arizona State University.
The discovery is described in a paper published in the Astrophysical Journal Letters.
Emma Softich et al. 2022. CWISE J014611.20-050850.0AB: The Widest Known Brown Dwarf Binary in the Field. ApJL 926, L12; doi: 10.3847/2041-8213/ac51d8
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