Brown dwarfs are the weird non-planets but non-stars in the universe, and astronomers have wondered for decades whether their atmospheres are streaked like Jupiter’s or spotty like the Sun’s. A team of astronomers at the University of Arizona used NASA’s TESS observatory to come up with the answer: If you saw a brown dwarf yourself, it would look more like a giant planet than a star.
Brown dwarfs are about the size of Jupiter, but much more massive. But they are not massive enough to sustain the fusion of hydrogen in their nuclei, so they do not qualify as stars. They float largely undetectable in the galaxy because they don’t emit much radiation.
Nevertheless, they are hot inside (generated by the heat left over from their formation) and cold outside (because space), so that the heat constantly flows outside. And when heat flows, weather happens.
But weather can happen in all sorts of ways, like the striped bands of Jupiter, the chaotic eddies of the earth, or the random spots of the sun. What kind are brown dwarfs?
Astronomers from the University of Arizona turned to NASA’s Transiting Exoplanet Survey Satellite (TESS), which normally hunts for exoplanets but is exquisitely tuned to study brown dwarfs as well. Using TESS, they observed the Luhman 16 system, a pair of orbiting brown dwarfs only 6.5 light years away.
By carefully studying the change in brightness of the Luhman 16 binary during its orbit, they were able to determine the patterns in its atmosphere. The result: streaked.
Jupiter gets its streaks from its rapid rotation. Warm flags of material rise from the interior, reach the edge of the atmosphere, cool off and sneak back down again. The rotation of the massive planet tightens these springs into rings, giving Jupiter its characteristic alternating stripes of material moving up and down.
Presumably something similar happens in the Luhman 16 system.
“If we know how the wind blows and redistributes heat in one of the best studied and closest brown dwarfs, we can better understand the climate, temperature extremes and development of brown dwarfs in general,” said lead author Daniel Apai , Associate Professor in the Department of Astronomy and Steward Observatory and the Lunar and Planetary Laboratory.
Further research will help astronomers determine if this is the status quo for brown dwarfs or if each is unique.
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