The climate map of a brown dwarf

A team of astronomers used the VLT (Very Large Telescope) at ESO to map the surface of the brown dwarf at just 6.6 light years from Earth, the third system closer to the Sun and the closest to be discovered since 1916. It was made a map of the light and dark areas on the surface of the star. The result was published in the January 30, 2014 in the journal Nature.

A weather map, the first ever of the surface of the brown dwarf closer to Earth, Luhman 16B, one of two brown dwarfs recently discovered in a couple close to the Sun, as obtained by a team of astronomers using the VLT (Very Large Telescope) at ESO and whose results were published in the January 30, 2014 in the journal Nature in a paper entitled “A global cloud map of the nearest known brown dwarf”.

Luhman 16B

Artistic representation of Luhman 16B derived from the VLT observations. The details of the surface were added to give an artistic effect. Credit : ESO/NASA/JPL

Brown dwarfs bridge the gap between the gas giant planets like Jupiter and Saturn, and the faint cool stars. They do not contain enough mass to start nuclear fusion in the core and can emit only weakly at wavelengths of infrared light. The first object as confirmed brown dwarf was found only twenty years ago and even now is only known from a few hundred of these elusive objects.

Now some astronomers have exploited the potential of the Very Large Telescope, not only to get a picture of these brown dwarfs, but also to build a map of the light and dark areas on the surface of Luhman 16B. Ian Crossfield, the Max Planck Institute for Astronomy (Heidelberg, Germany), the lead author of the new article, summed up the results: “The preceding observations suggested that brown dwarfs could have a patchy surface, but now we can actually build a map. Soon we will be able to observe the clouds that form, evolve, and dissipate on this brown dwarf – at the end of exoplanets meteorologists can predict whether a visitor to Luhman 16B could expect a clear or cloudy. ”

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Map of the surface of Luhman 16B reproduced from the VLT observations . Credit : ESO/NASA/JPL

Brown dwarfs closer to the solar system form a pair known as Luhman 16AB, located 6.6 light years from Earth in the southern constellation of Vela. This pair is the third system closer to our planet, after Alpha Centauri and Barnard’s Star, but it was only discovered in early 2013 by the American astronomer Kevin Luhman from images obtained from satellite WISE infrared survey. The official name is WISE J104915.57 – 531906.1. As Luhman had already discovered fifteen other double stars, has been used as Luhman 16. Following the convention for double stars, Luhman 16A is the brightest of the pair, while the secondary star is called Luhman 16B and the pair is referred to as Luhman 16AB. The weakest component, Luhman 16B, had already given indications that its brightness would change every few hours during the rotation – a clue that indicated the presence of particular characteristics of the surface.

To get the map of the surface, astronomers have used a clever technique: brown dwarfs observed with the instrument mounted on the VLT CRIRES and this has allowed them not only to see the changes in brightness during the period of rotation of Luhman 16B, but also to see if the structures of light and dark moved away or closer to the observer. Combining all of this information could recreate the arrangement of light and dark areas on the surface.

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The figure shows the object at six different times, with equal intervals, while it rotates once around its own axis . Credit : ESO/NASA/JPL

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