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Astronomers Detect Turbulent Bands of Clouds on a Brown Dwarf 6.5 Light-Years Away by using polarime
Time：2020-7-3 Source：Science Alert Author： Gilbert Cheung
A brown dwarf 6.5 light-years from Earth in the
constellation of Vela could be banded like a bumblebee butt. New observations
of the object seem to show stripes of clouds that circle its entire globe,
similar to those on Jupiter.
It's not the first time such bands have been detected on a brown dwarf - but it is the first time astronomers have made such a detection using polarimetry, taking measurements of objects based on the way the light they emit is twisted, or polarised.
It's not a new technique, but advances in technology and analysis techniques are giving it new life as a tool for understanding our cosmos, astronomers note.
"Polarimetry is receiving renewed attention in astronomy," said astronomer Dimitri Mawet of Caltech and the Jet Propulsion Laboratory.
"Polarimetry is a very difficult art, but new techniques and data analysis methods make it more precise and sensitive than ever before, enabling groundbreaking studies on everything from distant supermassive black holes, newborn and dying stars, brown dwarfs and exoplanets, all the way down to objects in our own Solar System."
A distance of 6.5 light-years is really small in astronomical
terms, but it's a long way away to try to pick out details on an object as
small and dim as a brown dwarf.
Brown dwarfs are an intermediate between planets and stars, and are often called "failed stars". They form the same way stars do - from the collapse of dense knots of material in cosmic gas clouds - but they're just not quite massive enough for hydrogen fusion in their cores.
Some of them could fuse deuterium, but they run out of fuel pretty quickly compared to 'real' stars; brown dwarfs are expected to undergo a cooling and contracting process similar to white dwarfs.
"Polarimetry is the only technique that is currently able to detect bands that don't fluctuate in brightness over time," Millar-Blanchaer said. "This was key to finding the bands of clouds on Luhman 16A, on which the bands do not appear to be varying."
The technique didn't allow the team to see the actual clouds. That would be amazing, but it's a little outside our capabilities at the present time.
Rather, the team took polarimetric measurements of the brown
dwarf, and then used sophisticated modelling to try to reproduce the
polarisation signature they observed. Two thick, permanent bands of clouds,
like those seen on Jupiter, were a close match.
And, like Jupiter, those clouds would be roiling, turbulent weather mess machines.
"We think these storms can rain things like silicates or ammonia. It's pretty awful weather, actually," said astronomer Julien Girard of the Space Telescope Science Institute.
And the research has implications well beyond Luhman A. As our instruments continue to improve, we may be able to use polarimetry to study the atmospheres of exoplanets, looking not just for weather, but to see whether we can identify the conditions for life.
Unfortunately, we probably won't find those on brown dwarfs though.
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