An ordinary brown dwarf near Earth turned out to be the rarest binary system of very massive planets - or a pair of not very massive dwarfs.
The discovery of a new large exoplanet today will surprise no one. But if a pair of such planets revolves around each other, and not around a star, this has never happened. Unsurprisingly, astronomers initially mistook them for a larger, lonely brown dwarf. Only now, in an article presented on the online preprint service ArXiv, scientists have revealed the true nature of this unique object.
Eugene Magnier of the University of Hawaii and his colleagues studied the brown dwarf 2MASS J11193254-1137466, an object larger than a planet but not large enough to be ignited by a thermonuclear reaction of hydrogen and become a star. It was discovered in 2015 about 85 light years from Earth. Surrounded by a cloud of hot dust left over from its birth, J1119-1137 is visible only in the infrared. Then astronomers noted its small (less than 15 masses of Jupiter) mass and - judging by the spectral characteristics - youth (about 10 million years). Therefore, J1119-1137 interested Magnier and his co-authors: they study such small and young dwarfs in order to better understand the processes of the appearance and evolution of stars and the boundary that separates real stars from "failed" brown dwarfs.
The observations were carried out with the Keck II 10-meter telescope located at the Keck Observatory in Hawaii and using an adaptive optical system that corrected for distortions associated with the influence of the Earth's atmosphere on light. This allowed us to consider that in fact J1119-1137 is a pair of bodies, slowly - making one revolution about once every 90 years - revolving around each other. The distance between them is about 3, 6 AU. e. - about 600 million km.
© Trent Dupuy, William Best, Michael Liu / Keck Observatory
Scientists have estimated the mass of both bodies at 3, 7 masses of Jupiter, so that, according to classical concepts, they belong to the planets, gas giants. The fact is that a "weak" thermonuclear reaction with the participation of deuterium takes place in the depths of brown dwarfs, but they are not large enough for a reaction with protons to take place, as in the Sun and other real stars. To start reactions with deuterium nuclei, the body needs to gain at least 13-14 Jupiter masses, so the border between the planets and brown dwarfs is usually drawn here.
On the other hand, the authors themselves, apparently, adhere to a more modern approach, which distinguishes large planets from small dwarfs not in size, but in origin. Planets are formed from a rotating protoplanetary disk; brown dwarfs, like stars - during the gravitational collapse of a gas and dust cloud. But no matter how we call J1119-1137 and whatever the origin of each member of the pair, it remains unclear how their tandem developed and how rare such a situation is in the Galaxy. Perhaps other bodies that appear as single brown dwarfs are binary systems of either large planets or small dwarfs.