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There is no doubt that Proxima Centauri, at a distance of 4.2 light years from the Sun, is the closest star. However, it is less certain which is the closest brown dwarf (though they are probably black or deep red, depending on their temperature) and it is still quite possible that one lies even closer than 4 light years away.
The Leibniz Institute for Astrophysics in Potsdam (AIP) is particularly interested in this possibility, and a few years ago they discovered Epsilon Indi Ba and Bb, the closest known brown dwarfs at about 12 light years away. An AIP researcher, Ralf-Dieter Scholz, and his colleagues, now report the discovery of another two brown dwarfs, WISE J0254+0223 and WISE J1741+2553, at distances of 15 and 18 light years respectively.
As the names of the two new arrivals indicate, they were first observed by the Wide-field Infrared Survey Explorer (WISE), that took the images shown above in 2010. The two brown dwarfs, at the centre of each image, attracted the attention of Scholz's team because of their high infrared luminosity, accompanied by very faint optical luminosity, implying very cool temperatures.
By comparing the positions of the same objects in the 2MASS and SDSS catalogues, made several years earlier, the researchers noted that the two objects had moved across the sky with a proper motion of 2.5 and 1.5 arcseconds per year. The objects positions in 2000 are indicated in each of the above images.
The large proper motions and colour of the objects was immediately sufficient to identify them as very nearby brown dwarfs, but confirmation came with spectroscopic observations made with the new Large Binocular Telescope in Arizona.
Like any type T and Y brown dwarfs, WISE J0254+0223 and WISE J1741+2553 are particularly cold, far below the temperatures needed to generate energy, and they are destined to cool slowly and become almost invisible.
One can't help but suspect that there are more of these failed stars even closer to the Sun than Proxima Centauri, perhaps too faint to be detected by present day instrumentation. |
