A team of astronomers, led by Arizona State University undergraduate student Emma Softich, has discovered a rare pair of brown dwarfs that has the widest separation of any brown dwarf binary system found to date.
Brown dwarfs are celestial objects that are smaller than a normal star and without sufficient mass to sustain nuclear fusion, but that are hot enough to radiate energy. Many brown dwarfs have been discovered with data from NASA’s Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, which solicits help from the public to search the WISE image data bank to find brown dwarfs and low-mass stars, some of the sun’s nearest neighbors.
For this study, the team made a series of images of Backyard Worlds discovery, which showed possible brown dwarfs that were not seen. In so doing, they discovered a rare brown dwarf binary system (CWISE J014611. 20 050850.0AB).
“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 co-author Adam Schneider of the U.S. Flagstaff Station, Naval Observatory and George Mason University.
For this study, lead author Softich, who is an astrophysics student at ASU’s School of Earth and Space Exploration, went through about 3,000 brown dwarfs from Backyard Worlds one by one and compared the WISE images to other survey images, looking for evidence of a brown dwarf companion to the original target. The team then used data from the Dark Energy Survey (DES) to confirm that it was indeed a brown dwarf pair.
They then used the Keck Observatory’s Near-Infrared Echellette Spectrometer (NIRES) to confirm that the brown dwarfs have spectral types L4 and L8, and that they are at an estimated distance of about 40 parsecs (130.4 lightyears) from Earth, with a projected separation of 129 astronomical units, or 129 times the distance between the sun and the Earth.
This distance makes CWISE J014611. 20-050850.0AB the widest brown dwarf pair found to date, with a separation of around 12 billion miles, three times the separation of Pluto from the sun.
“Because of their small size, brown dwarf binary systems are usually very close together,” Softich said. It is exciting to find such a separated pair.
The gravitational force between two brown dwarfs is also lower than that between stars with the same separation. Wide brown dwarf binaries are therefore more susceptible to being disrupted over time. This makes this pair of brown-dwarfs an extraordinary find.
The team hopes that this discovery will give astronomers the opportunity to study brown dwarf binary system and to create models and procedures to aid in their recognition in the future.
“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 co-author Jennifer Patience, who is Softich’s adviser at ASU.