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Brown dwarf shows Jupiter like cloud bands

Brown dwarfs are those objects that are lighter than the stars but heavier than the planets. They typically have the 13 to 80 times the mass of the Jupiter.

May 7, 2020 16:22 IST
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The team of astronomers has recently discovered that Luhman 16A, the closest brown known dwarf, has been showing the signs of cloud bands. They are similar to those seen on Saturn and Jupiter.

The technique of polarimetry has been used for the first time by the scientists in order to determine the properties of atmospheric clouds that are outside of the exoclouds or solar system.

Brown dwarfs are those objects that are lighter than the stars but heavier than the planets. They typically have the 13 to 80 times the mass of the Jupiter.

Luhman 16A: Important Details

Luhman 16A has been a part of the binary system that also contains a second brown dwarf i.e. Luhman 16B. After Alpha Centauri and Barnard’s star, it has been the third closest system to our sun, at a distance of 6.5 light-years.

Even having similar masses and temperature and presumably have been formed at the same time, Luhman 16A and 16B have shown different weather. Luhman 16B, instead of exhibiting the evidence of more irregular and patchy clouds, has not shown any signs of stationery cloud bands. Therefore, it has more noticeable brightness variations because of its cloudy features, unlike Luhman 16A.

Julien Girard, a member of the discovery team stated that like Earth and Venus, they are twins but have very different weather. He further added that it can rain things like silicates and ammonia, making pretty awful weather.

How the cloud bands were discovered?

To study the polarised light from Luhman 16 system, researchers used an instrument on the very large telescope in Chile.

Polarisation is basically a property of light that represents the direction in which the light wave oscillates. To reduce the glare and improve the contrast, polarised glasses block out the one direction of polarisation. As per the lead author, Max Millar- Blanchaer, instead of trying to block that glare, we have been trying to measure it.

When the light is reflected off of particles, like cloud droplets, it can go for a certain angle of polarisation. Astronomers can easily deduce the presence of clouds without resolving directly either of the brown dwarf’s cloud structure, by measuring a preferred polarisation of light from a distant system. The polarisation can be used, even from light-years away, to determine what the light had encountered along in its path.

Result of the observation:

In order to determine, what the light had encountered on its way, there was a comparison between the observations against models with different properties- striped cloud bands, brown dwarf atmospheres with solid cloud decks, and even the brown dwarfs that have been oblate due to their fast rotation. It was found that only the models of atmospheres with cloud bands were a match to the observations of Luhman 16A.

The polarimetry technique has not been limited to the brown dwarfs. The technique can also be applied to the exoplanets orbiting distant stars.

Some essential highlights of the study:

•  James Webb Space Telescope, NASA’s upcoming telescope will be able to study systems like Luhman 16 in order to look for the signs of brightness variations in infrared light that have been indicative of cloud features.

•  NASA’s Wide-Field Infrared Survey Telescope (WFIRST) will come equipped with a coronagraph instrument that will be able to conduct polarimetry.

•  The study has been accepted for publication in The Astrophysical Journal.

•  The Space Telescope Science Institute (STScl) has been expanding the frontiers of space astronomy by hosting the science operation centre for the James Webb Space Telescope, science operation centre of Hubble Space Telescope, and the science operation centre for the future Wide Field Infrared Survey Telescope (WFIRST).

•  STScl has also been housing the Mikulski Archive for Space Telescopes (MAST). It is a NASA funded project that will provide the astronomical community a variety of astronomical data archives. It is also the data repository for the Webb, Hubble, K2, Kepler, Tess missions, and many more.

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