Astronomers discovered rare eclipse of double brown dwarf system

Astronomers working on "first light" data from a newly commissioned telescope in Chile made a chance discovery that led to the identification of a rare eclipse of two brown dwarfs. The result was published today in the journal Nature Astronomy.

Sometimes called "failed stars," brown dwarfs occupy a grey zone between stars and giant planets. They are unable to sustain the fusion of hydrogen into helium, a process that powers the light from normal stars like the Sun; yet they appear to form like stars, only with less mass. They provide a critical link in scientists' understanding of star and planet formation.

The chance discovery was led by an international team of researchers, including scientists at UC San Diego, working on a project called SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars), which aims to find planets orbiting the smallest stars, including brown dwarfs. SPECULOOS finds planets by detecting periodic dips in a star's brightness as a planet passes in front of it, an event called a planetary transit.

Astronomers predict that the smallest stars and brown dwarfs could host large populations of close-in, potentially habitable rocky planets, like the famous seven-planet system TRAPPIST-1 that was discovered in 2017 by members of the same team.

"This is a great example of scientific serendipity," explained Adam Burgasser, professor of physics at UC San Diego and co-leading author on the study. "While searching for planets, we found an eclipsing brown dwarf binary, a system that is uniquely suited for studying the fundamental physics of these faint celestial objects."

Soon after the construction of the first SPECULOOS telescopes in Chile, and during early testing observations, the team targeted the brown dwarf "2MASSW J1510478-281817," also known as 2M1510, in the constellation Libra. In this case, the SPECULOOS observations picked up a distinct signal that led the researchers to speculate that 2M1510 might be two brown dwarfs instead of one, in orbit around each other.

"Among the first test observations we performed, we turned one of our telescopes to a known brown dwarf. But suddenly the object appeared to get dimmer for about 90 minutes, which indicated an eclipse just took place," reported Michael Gillon, principal investigator of the SPECULOOS project.

Artem Burdanov, a postdoctoral researcher at Massachusetts Institute of Technology and co-author on the study concurred, adding, "We rapidly realized that we were probably looking at two eclipsing brown dwarfs, one passing in front of the other, a configuration which is much rarer than planetary systems."