A very cool methane-rich brown dwarf and a dying white dwarf star have been found orbiting each other by astronomers using the United Kingdom Infrared Telescope (UKIRT), the Gemini Observatory and the European Southern Observatory’s Very Large Telescope.

The exotic system is the first of its type to be discovered, and provides astronomers with insight into the ‘T-dwarf’ population of stars – those which are rich in methane and on the cusps between a planet and star. Methane is only seen in cool stars and gas planets like Jupiter, but T-dwarfs are too cool to permit the same chemical reactions needed to fuel a star like our own Sun. Instead they simply fade over time.

The newly discovered system is around five billion years old, and the T-dwarf has a mass of about 70 Jupiters, and a temperature of approximately 1,000 degrees Celsius. The two stars are bound together by only a weak gravitational attraction – separated by 2.5 trillion kilometres, although would have been much closer together in the past.

The white dwarf component of this system was once a star like our Sun, but has exhausted its fuel supply and expelled its outer layers away into space, leaving a very small but extremely dense core. The loss of mass would have weakened the gravitational pull between the stars, causing the methane dwarf to spiral outwards into the configuration observed today.

“Binary systems like this provide vital information and allow us to better understand ultra-cool atmospheres and the very low-mass dwarfs and planets they enshroud,” says Dr. David Pinfield of the University of Hertfordshire. “The fact that these binaries survive intact for billions of years means that we could find many more lurking out there in the future.”

The system resides about 160 light years away in the constellation of Virgo.