A publication in Nature Astronomy

SPECULOOS telescopes pinpoint a rare eclipsing binary brown dwarf

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Artistic view of WISE 0855 as it might appear if viewed up close in infrared light.©Joy Pollard, Gemini Observatory/AURA

An international team of scientists including researchers from the University of Liège has just identified an eclipsing binary brown dwarfs with the telescopes of the SPECULOOS project led by Michaël Gillon, researcher at the University of Liège. This rare discovery - only one other binary system of this type had been discovered more than 10 years ago - has just been published in the journal Nature Astronomy.


n international team of scientists, led by Amaury Triaud, a researcher at the University of Birmingham, has just made an important discovery: an eclipsing binary system composed of two brown dwarfs in eclipse, one of them passing in front of the other at each orbit. Brown dwarfs are so-called "sub-stellar" objects, they form like stars but have too little mass to allow nuclear fusion in their core, the process that characterizes normal stars. Although scientists believe that brown dwarfs are widespread in the universe, they are still difficult to detect because of their low luminosity. In this case, the observations were obtained shortly after the construction of the first telescopes, while they were still in the test phase," explains Michaël Gillon, astronomer at the University of Liège (ASTROBIOLOGY / Faculty of Science), initiator and principal investigator of the SPECULOOS project (Search for habitable Planets EClipsing ULtra-cOOl Stars), at the origins of the discovery. We had turned one of our telescopes in Chile toward a known brown dwarf (2MASSW J1510478-281817) and observed a decrease in brightness of this object for about 90 minutes, indicating that an eclipse had just occurred." A signal that enabled the researchers to conclude to the binary nature of the brown dwarf.

We were able to confirm our hypothesis by using two more powerful telescopes: the Keck, a 10-metre diameter telescope located in Hawaii and the Very Large Telescope of 8 metres located in Chile, a few kilometres from our SPECULOOS-South Observatory," says Laetitia Delrez, a researcher at ULiège (ASTROBIOLOGY and STAR Institute). Observations of eclipsing binary brown dwarfs are extremely rare - only one other similar system has been identified, more than 10 years ago. "This configuration will allow astronomers to measure their radius and mass without making assumptions, they have already been able to measure the individual velocities of the two brown dwarfs, allowing them to constrain their masses.  "In addition to their radii, obtained from the eclipse and luminosity, we were also able to estimate their age - around 50 million years-, which is really rare because usually in the measurements of these objects, at least one other element is missing," explains Dr Amaury Triaud, researcher at the School of Physics & Astronomy at the University of Birmingham, who led the analysis.

The team that the produced the discovery consists of researchers from the University of Birmingham, the University of California, San Diego, the University of Liège, the Institute of Astrophysics of the Canaries, the American Museum of Natural History, the University of Cambridge, the University of Bern, the Massachusetts Institute of Technology, the University of Göttingen and the University of Warwick.

Scientific reference

TRIAUD & al., A SPECULOOS Discovery of an Eclipsing Substellar Binary in a Young Triple System, Nature Astronomy, Volume 4, Issue 3, 9 March 2020


University of Liège

Michaël GILLON | ASTROBIOLOGY | Faculté des Sciences

Laetitia DELREZ | ASTROBIOLOGY | STAR Research Institute | Faculté des Sciences

University of Birmingham



Brown Dwarves SPECULOOS Amanda J. Smith 

Artist's view from one of the SPECULOOS telescopes, with the two brown dwarves in the sky. The third red dot, is a third brown dwarf nearby, which is also part of the same system. The book on the side shows the data that led to this discovery. The left page shows the eclipse captured by SPECULOOS while the right page shows the data from Keck and the VLT.
© University of Birmingham / Amanda J. Smith

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