“Astronomers’ sunglasses” spot stripy clouds in brown dwarf atmosphere

Using polarized light, astronomers have detected signs of cloud bands in the atmosphere of a brown dwarf far beyond the solar system. It turns out that these gassy giants have a similar appearance to Jupiter, and the same kind of wild weather.

Caught in the middle ground between planets and stars, brown dwarfs are enigmatic objects. They form in the same way as stars, when pockets of gas and dust clouds collapse under their own gravity. Stars eventually collect enough mass to create tremendous pressure and heat, igniting the core with nuclear fusion.

But brown dwarfs don’t make it quite that far. While they end up with much larger masses than Jupiter – up to 80 times more, in fact – that’s still not enough for them to fire up as a star. Instead, they find themselves stuck as a cool ball.

Brown dwarfs occupy the middle ground between planets and stars
Brown dwarfs occupy the middle ground between planets and stars

NASA/JPL-Caltech/R. Hurt (IPAC)

Now, a new study has shown just how Jupiter-like brown dwarfs can be. A team of astronomers has used the Very Large Telescope (VLT) in Chile to look for signs of clouds in the atmosphere of Luhman 16A, the closest brown dwarf to Earth. It’s part of a binary system of brown dwarfs, located a celestial stone’s-throw away at just 6.5 light-years.

The team studied the object by measuring the polarization of light coming from it. Light that radiates from its warm surface scatters off molecules in the atmosphere, polarizing it in a certain way. Polarimetric instruments, which the team describes as “astronomer’s sunglasses,” can then tell if this polarization is uniform across the whole object, or if it’s stronger in some parts than others.

In this case, the signals were stronger in some parts, indicating cloud bands streaking across the Luhman 16A. However, it didn’t reveal how many bands there were. To figure that out, the researchers modeled different cloud band patterns, and the one that most closely matched the brown dwarf’s light imprint was for two large bands.

That pattern is similar to what we see on Jupiter. The models also suggested that these clouds would create storms where it rains silicates or ammonia.

With the current study acting as a proof of concept, the team says that studying polarized light could help give us a better understanding of the clouds, atmospheres and, ultimately, habitability of exoplanets. That could be invaluable in the search for alien life.

“Polarimetry is very sensitive to cloud properties, both in brown dwarfs and exoplanets,” says Maxwell Millar-Blanchaer, lead author of the study. “This is the first time that it’s really been exploited to understand cloud properties outside of the solar system.”

The research was published in The Astrophysical Journal. The team describes the work in the video below.

Astronomers Use “Sunglasses” to Find Cloud Bands on a Brown Dwarf

Sources: Caltech, Hubble

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