There is an intruder among the brown dwarfs

An international team of researchers studied the binary system Luhmann 16AB where two brown dwarfs (objects of mass greater than Jupiter but too inferior to the sun to light up like stars) are orbiting each other in only 6.6 years light from the Earth. Astronomers have discovered that the orbits are disturbed by a third object, which could be added to the star system.


Digitized Sky Survey


By studying in detail a couple of “failed stars” near the Sun, a team of astronomers has suggested the existence of a third hidden object, similar to the mass of a planet. The failed stars known as brown dwarfs are better: they are stars that have a mass greater than that of a planet like Jupiter, but less than 8% of that of the Sun that is not reaching the 70 Jupiter masses, because it has the minimum mass place in their nuclear fusion of stars (so to trigger the burning of hydrogen into helium).

This particular binary system studied by the researchers is called Luhman 16AB, discovered at the beginning of 2013 to just 6.6 years light from Earth. Over the months, several astronomers have studied the two brown dwarfs to define their characteristics. After two months of observation, the team which includes Yuri Beletsky from Carnegie University has found that both objects have a mass between 30 and 50 Jupiter masses. In comparison, the Sun has a mass of about 1.000 Jupiter masses.

“The two brown dwarfs are separated by a distance equivalent to three times that between the Earth and the Sun. The two brown dwarfs are gravitationally bound and orbit one another. Since they have such small mass, it takes about 20 years to complete their orbit, “said Beletsky.

The team, led by Henri Boffin from the European Southern Observatory (ESO), has used the instrument FOR2 mounted on ESO’s Very Large Telescope (VLT) in Chile to photograph the pair of brown dwarfs , every 5 or 6 days between 14 April and 22 June this year (2013). As the instrument has allowed the observers to make very precise measurements, the scientists were able to detect small shifts of the two objects already in orbit during these two months. Astronomers were able to measure the positions of the two brown dwarfs with a precision ten times greater than before, and therefore they have also detected the small perturbations of their orbit.



Composite infrared images

Credit: NASA/JPL/NSF/Gemini

The researchers were able to see some small deviations from the expected orbital motion. From these small changes in both orbits of brown dwarfs, astronomers conclude that there may be a third object to keep company to the two failed stars. It may be a heckler from the crowd like a planet, which has an orbital period from two months to one year. With future observations, the theory could be confirmed: it is very likely that this is a third brown dwarf and then Luhman 16AB becomes a ternary star system.

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