Bold banding may be a common feature of brown dwarf skies.
Scientists have spotted evidence of Jupiter-like stripes in the thick atmosphere of a nearby brown dwarf, a new study reports — and this evidence was gathered in a novel way.
Brown dwarfs are bigger than planets but not big enough to host fusion reactions in their interiors. For this reason, these curious objects are also known as "failed stars."
NASA's recently retired Spitzer Space Telescope previously detected banding patterns on multiple brown dwarfs, by tracking in detail how the objects' brightness varied over time. But in this new study, scientists inferred banding via polarimetry, the measurement of polarized light.
Polarized light oscillates in the same direction rather than in multiple, random avenues the way "normal" light does. Polarimetric instruments take advantage of this alignment, much as polarized sunglasses do to reduce the glare of light from Earth's star.
The study team used a polarimetric instrument on the European Southern Observatory's Very Large Telescope (VLT) in Chile to study the brown dwarf Luhman 16A, which is about 30 times heftier than Jupiter. The failed star is part of a brown-dwarf binary; it and its similar-sized partner, Luhman 16B, are the nearest such pair to Earth, a mere 6 light-years away.
The VLT instrument, known as NaCo, detected an excess of polarization in the brown dwarf's light. That's a strong indication of atmospheric banding, researchers said. After all, the light was unpolarized when it was first emitted deep within Luhman 16A, becoming polarized by scattering off haze particles high in the brown dwarf's skies. In a uniform, unbanded atmosphere, this polarization would average out into an unpolarized glow.
The scientists further interpreted the VLT observations using sophisticated computer models of Luhman 16A's thick atmosphere. The combined work suggests that the brown dwarf is striped, perhaps with two major, broad bands, researchers said.
"Polarimetry is the only technique that is currently able to detect bands that don't fluctuate in brightness over time," study lead author Maxwell Millar-Blanchaer, a postdoctoral astronomy researcher at the California Institute of Technology (Caltech) in Pasadena, said in a statement. "This was key to finding the bands of clouds on Luhman 16A, on which the bands do not appear to be varying."