An international team of astronomers has found a needle-in-a-haystack stellar system just 119 light-years from Earth. The system contains not one but three brown dwarfs, stellar objects that were never massive enough to begin nuclear fusion at their core and become full-fledged stars (often refered to as failed stars).

More importantly, two of these failed stars are eclipsing binaries, a setup that provides researchers with insights into the nature of the celestial bodies. An eclipsing binary happens when two failed stars are aligned in the line of sight we see them, so they constantly eclipse each other. 

The system, known as 2M1510, was one of the very first discovered in the project called SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars). The goal of the project is to find terrestrial planets around the smallest of stars and brown dwarfs by looking at planets eclipsing their star. However, it seems to work well in identifying eclipsing binaries too.  

“From the very first spectrum we obtained, we could tell we had an exciting binary discovery,” co-leading author Adam Burgasser, from UC San Diego, said in a statement. “It was thrilling to see the absorption lines move back and forth in perfect synchronicity, which allowed us to measure the mass of the binary.”

The research has brought an unprecedented level of certainty into the measurements of these two objects. The team worked out that the failed stars are 45 million years old, with a mass that's around 4 percent of the Sun and a diameter of about 220,000 kilometers (136,000 miles). The measurements also allowed researchers to put theories about brown dwarfs to the test.

“Collecting a combination of mass, radius, and age is really rare for a star, let alone for a brown dwarf,” explained Amaury Triaud, a Birmingham Fellow at the University of Birmingham in the UK, who was the primary author of the study. “Usually one or more of these measurements is missing. By drawing all these elements together, we were able to verify theoretical models for how brown dwarfs cool, models which are over 30 years old. We found the models match remarkably well with the observations, a testament to human ingenuity.”

The team also provided corrections to some of the models, which they said should be taken into account in estimations of future brown dwarf properties. The findings are reported in Nature Astronomy.