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Weather out of this world

Astronomers have found the first hints that failed stars known as ‘brown dwarfs’ may have weather patterns with winds, clouds and storms. This was announced today by Dr Chris Tinney at ScienceNOW! in Melbourne.

Dr Tinney of the Anglo-Australian Observatory and Mr Andrew Tolley, a student at the University of Oxford, recently observed a brown dwarf and noted changes in its surface chemistry as it rotated. They made their observations with Australia’s largest optical telescope, the Anglo-Australian Telescope (AAT), located at Siding Spring outside Coonabarabran NSW.

The left panel shows the weather patterns we might expect on a brown dwarf if it looked like Jupiter. The right panel shows observed variations seen as the brown dwarf LP944-20 rotates. The arrows highlight strong episodes of cloud passage where very different signals are seen in the two colours observed.

Brown dwarfs are failed stars with masses in between that of Jupiter-like planets and normal stars. For decades, scientists have suspected that brown dwarfs exist but the first confirmed detection came only a few years ago. Today, after 30 years of searching, less than 50 brown dwarfs have been discovered. Of these, only a handful are bright enough and close enough to be studied for weather.

Tinney’s team is leading Southern Hemisphere attempts to learn more about brown dwarfs. They are very faint, and extremely difficult to detect, and for Tinney and Tolley to have noted surface changes is remarkable.

Brown dwarfs never made it as stars, being too small to light up their nuclear furnaces. Instead, they just smoulder away in space at temperatures below 2000 degrees — less than a third that of a typical star like the sun. ‘Proper’ stars are so hot that their surfaces are a completely smooth mix of vapourised material. But the outer layers of brown dwarfs are cool enough for chemicals to ‘rain’ out as smoke-like particles.

Tinney said, “Brown dwarfs are too small and far away to see the clouds. We detected them indirectly through the effects they have on the brown dwarf’s atmosphere. We looked for a changing pattern of chemistry in the atmosphere of one brown dwarf, called LP944-20, as it rotated.”

With a special instrument developed by the AAT, called the Taurus Tuneable Filter, Tinney and Tolley were able to ‘tune into’ a very narrow wavelength band and accurately measure tiny fluctuations. The narrow band chosen matched that of a tracer molecule called titanium oxide. The strength of this tracer allowed astronomers to track the formation of cloud particles.

Now that the technique has been honed, the astronomers are looking to other brown dwarfs. “We plan to study at least two more brown dwarfs in the next few months,” Tinney concluded.

Background material on brown dwarfs

Background material on titanium oxide

Information and photos are also available on the ScienceNOW! website

For further information contact
Roger Bell, Public Relations Officer, Anglo-Australian Observatory
(02) 9372 4865

Dr Chris Tinney, email
(02) 9372 4849 (Office),May 3-5, May 6 (9am-2pm),May 11-14
0416 092117    (Mobile),May 6 (4pm) - May 10

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