NASA's Webb telescope has discovered indications of potential aurorae on a solitary brown dwarf.
Aurorae on Earth are formed when energetic particles from
the Sun are captured by Earth's magnetic field and interact with gas molecules
in our atmosphere, creating mesmerizing curtains of light. Similarly, Jupiter
and Saturn also experience auroral processes involving interactions with the
solar wind, as well as contributions from their active moons. However, for
isolated brown dwarfs like W1935, the absence of a stellar wind poses a mystery
as it cannot explain the extra energy required for methane emission in the
upper atmosphere. The team suggests that internal processes or external
interactions with interstellar plasma or a nearby active moon may account for
this emission.
Just because you’re cold and lack a star doesn’t mean you’re not capable of cool things! We're looking at you, W1935. #AAS243
— NASA (@NASA) January 10, 2024
A discovery using @NASAWebb has found a brown dwarf with infrared emission suggesting atmospheric heating by auroral processes: https://t.co/5fDMUMIZpl pic.twitter.com/B1SLpz1Snk
The discovery of aurorae in brown dwarfs unfolded like a
detective story. Jackie Faherty, an astronomer at the American Museum of
Natural History in New York, led a team that was granted time with the Webb
telescope to study 12 cold brown dwarfs. One of these objects, W1935, was
discovered by citizen scientist Dan Caselden through the Backyard Worlds
zooniverse project, while W2220 was discovered using NASA's Wide Field Infrared
Survey Explorer. Detailed observations with the Webb telescope revealed that
W1935 and W2220 were remarkably similar in composition, brightness,
temperatures, and spectral features. However, the notable difference was that W1935
exhibited methane emission instead of the expected absorption feature observed
in W2220. This unique emission was detected at a specific infrared wavelength
that the Webb telescope is particularly sensitive to.
Faherty expressed her surprise at the discovery of
methane emission on the brown dwarfs, as they had expected to observe methane
absorption instead. She questioned the reason behind this unexpected
phenomenon. To investigate further, the team utilized computer models to
analyze the emission. The models revealed that W2220 exhibited an anticipated
energy distribution throughout its atmosphere, with decreasing temperatures at
higher altitudes. However, W1935 presented an intriguing outcome. The most
accurate model indicated a temperature inversion, where the atmosphere became
warmer with increasing altitude. This temperature inversion puzzled the
researchers, as it is typically observed in planets with a nearby star that can
heat the stratosphere. The absence of an apparent external heat source in this
object made the finding even more remarkable. Ben Burningham, a co-author from
the University of Hertfordshire in England and the lead modeler, emphasized the
wild nature of this discovery.
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