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article imageAstronomers map weird brown dwarf where molten iron rains

By Robert Myles     Jan 31, 2014 in Science
Heidelberg - An international team of astronomers has produced the first ever map of the weather on the surface of the nearest astronomical oddity, known as a brown dwarf, to Earth.
Brown dwarfs are neither stars nor planets. They fill the gap between giant gas planets, of which Jupiter and Saturn are examples in our own solar system, and faint cool stars. Even in cool stars nuclear fusion reactions take place, converting hydrogen to helium, and in the process emitting light.
Brown dwarfs, on the other hand, are the damp squibs of the cosmos. They don’t contain sufficient mass for their cores to initiate nuclear fusion. Unlike our sun, which emits light at higher frequencies, brown dwarfs resemble the dying embers of a fire, glowing feebly at infrared wavelengths of light.
Because they glow so faintly, brown dwarfs are difficult to detect. Although their existence was theorized in the 1960s, and various brown dwarf candidates emerged subsequently, the discovery of the first confirmed brown dwarf had to wait until 1994 when three Spanish astrophysicists identified an object they called Teide 1, in the Pleiades open cluster.
To date, only a few hundred brown dwarf objects have been confirmed.
Astronomers used the European Southern Observatory’s (ESO) Chile-based Very Large Telescope (VLT), the world’s most advanced visible-light astronomical observatory, to map the recently discovered brown dwarf, which forms one of a pair.
The VLT array was used to target the brown dwarf object known as Luhman 16B. Dark and light features on Luhman 16B, whose less snappy astronomical name is WISE J104915.57-531906.1B, were plotted by the astronomers.
Another interesting feature of the discovery is that, in astronomical terms, the brown dwarf pairing, known as Luhman 16AB, in the southern constellation of Vela (the Sail), is pretty much in our precinct of the Milky Way, being a mere six light years distant. Only the Alpha Centauri system (at 4.37 light years) and Barnard’s Star (at 5.98 light years) lie closer to our sun.
After the Luhman 16AB pair was discovered in 2013, observations of the fainter Luhman 16B found that its brightness changed slightly every few hours as it rotated, providing a clue that it might have marked surface features.
The ESO’s VLT array was then trained on the brown dwarfs and used to map out the dark and light features on the surface of Luhman 16B.
To map Luhman 16B’s surface, astronomers used the CRIRES — cryogenic high-resolution infrared echelle spectrograph — instrument on the VLT. The CRIRES allowed the researchers not just to see the changing brightness as Luhman 16B rotated, but also to see whether dark and light features were moving away from, or toward the observer. All this information was combined to recreate a map of the dark and light patches of the surface.
Summarizing the results, Ian Crossfield, based at the Max Planck Institute for Astronomy in Heidelberg, Germany and lead author of the results published Jan. 30 in the journals Nature and Astrophysical Journal Letters, said, “Previous observations suggested that brown dwarfs might have mottled surfaces, but now we can actually map them. Soon, we will be able to watch cloud patterns form, evolve, and dissipate on this brown dwarf.”
The maps produced by the research team are reminiscent of crude satellite weather maps of Earth but, with ever-larger telescopes being built and coming on stream over the next few years, Crossfield forecast, “Eventually, exometeorologists may be able to predict whether a visitor to Luhman 16B could expect clear or cloudy skies."
Surface map of Luhman 16B recreated from VLT observations. ESO s Very Large Telescope has been used ...
Surface map of Luhman 16B recreated from VLT observations. ESO's Very Large Telescope has been used to create the first ever map of the weather on the surface of the nearest brown dwarf to Earth. The figure shows the object at six equally spaced times as it rotates once on its axis
ESO / I. Crossfield
Cloudy it may be on Luhman 16B, but it’s unlikely any human will ever set foot there. The temperature of the clouds detected by Crossfield and his colleagues is estimated at around 1,100°C. But even if a sufficiently heatproof spacesuit were ever devised, astronauts would likely have to contend with Luhman 16B’s inhospitable drizzle.
On Luhman 16B, a hard rain falls, literally. For exometeorologists speculate that what passes for rain on Luhman 16B consists of minute droplets of molten iron and various minerals, floating in an atmosphere of mainly hydrogen.
In a parallel study, led by Beth Biller at the University of Edinburgh in Scotland, the atmospheres of both Luhman 16A and Luhman 16B were examined at greater depths, enabling researchers to reconstruct what happens in different layers of the atmosphere for both Luhman 16A and 16B.
Biller commented, “We've learned that the weather patterns on these brown dwarfs are quite complex. The cloud structure of the brown dwarf varies quite strongly as a function of atmospheric depth and cannot be explained with a single layer of clouds."
Biller saw the mapping of Luhman 16AB as just the start for exocartography. Looking ahead, she added, “We are excited by what we have been able to see in these studies, but this is only the start. With new generations of telescopes, such as the forthcoming European Extremely Large Telescope, astronomers will likely see surface maps of more distant brown dwarfs -- and eventually, surface maps for young giant planets.”
Astronomers might not have too long to wait. Although its installation has been subject to delays, 2014 should see the new SPHERE instrument installed at the VLT. SPHERE, short for Spectro-Polarimetric High-contrast Exoplanet Research, will be dedicated to exoplanet research and should be capable of mapping objects like Luhman 16AB in far greater detail than has been possible up till now.
The ESO Very Large Telescope (VLT) during observations. A reddish laser beam is launched to create a...
The ESO Very Large Telescope (VLT) during observations. A reddish laser beam is launched to create an artificial star at an altitude of 90 km in the Earth´s mesosphere. This Laser Guide Star (LGS) allows astronomers to remove the effects of atmospheric turbulence, producing images almost as sharp as if the telescope were in space.
ESO - Serge Brunier.
More about brown dwarfs, Exoplanets, Luhman 16AB, European southern observatory, Eso
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