A team of astronomers at the University of Hawaii led by William Best found a couple of “planetary mass objects” orbiting each other rather than orbiting a star. An object at first thought to be a single brown dwarf is actually a pair of two objects of equal flux orbiting each other.It’s not yet clear how this binary system formed, however the discovery might help redefine the line between planets and brown dwarfs – failed stars with tens of times the mass of Jupiter.
The pair J11193254–1137466 was announced last year as an unbound planetary-mass system resides in a cluster of 30 young stars about 95 light-years away from Earth called the TW Hydrae Assocation. 1137466 is around 160 light-years away, however its motion indicates an 80 % chance that it’s a part of this grouping of young stars.
This pair of planets is made up of two balls of gas the size of Jupiter but almost four times more massive, separated by some 600 million kilometers, and slowly circling each other once per century or so. The young couple only emits light at infrared wavelengths, with residual heat from their formation, just 10 million years ago.
The team found that each component is a mere ~3.7 Jupiter masses, placing them in the fuzzy region between planets and stars. While the International Astronomical Union considers objects below the minimum mass to fuse deuterium (around 13 Jupiter masses) to be planets, other definitions vary, depending on factors such as composition, temperature, and formation. The authors describe the binary as consisting of two planetary-mass objects.
Regardless of its definition, 2MASS J11193254–1137466AB qualifies as the lowest-mass binary discovered to date. The individual masses of the components also place them among the lowest-mass free-floating brown dwarfs known. This system will therefore be a crucial benchmark for tests of evolutionary and atmospheric models for low-mass stars in the future.