American researchers might have found the first example of binary exoplanets orbiting each other. A study describing the research, yet to be published, was presented this summer at the American Astronomical Society Meeting, and picked up recently by Space.com.
The two rogue objects, which do not appear to orbit a star, straddle the definition between gas planets and brown dwarfs. The former includes planets like Jupiter and Saturn, while the latter are stellar objects that are not massive enough to become fully fledged stars.
Although they each have about 15 times the mass of Jupiter, these objects are 65 light-years away and they are very dim – a needle in a very large and dark haystack.
The discovery is part of a larger project looking into brown dwarf binaries. By studying binary objects, astronomers are capable of establishing properties with more accuracy, so they become a perfect testing ground for their theories.
The team, led by Daniella Bardalez Gagliuffi from the University of California, San Diego, has been looking at these brown dwarf binaries to better understand how planets evolve. Brown dwarfs are thought to form like stars, but as they cool down they become more and more planet-like.
And one of these low-temperature objects appeared to have a previously unresolved companion, which is a very interesting finding. The binary system is part of a young group of stars, and discovering two of them so close to each other suggests that they formed together, a fact that also plays an important role in understanding their properties.
“Given that they're so close, it's extremely likely that they're bound,” Gagliuffi told Space.com. “They're probably brother and sister.”
Gravitationally bound objects tend to form at the same time. Combining this information with their luminosity and mass, we can work out how they have changed over the years.
More observations are needed to confirm the nature of this system, though. Finding a pair of binary rogue planets would be incredible, but even if they turn out to be “just” brown dwarfs, they would be on the smaller scale for these types of objects.