NASA's Webb telescope has discovered indications of potential aurorae on a solitary brown dwarf.

 NASA's Webb telescope has discovered indications of potential aurorae on a solitary brown dwarf.

Credit Image:A visual representation created by an artist depicts a spherical, gaseous entity set against a backdrop of a dark expanse filled with stars. This entity, known as a brown dwarf, dominates the right side of the image. Its surface exhibits a range of deep blue hues and is adorned with sinuous, horizontal bands that wrap around it, reminiscent of the distinctive features found on Jupiter, a planet within our own solar system. The brown dwarf is positioned at a slight tilt towards the right and towards the observer, allowing for the complete visibility of one of its poles. Encircling this pole is a vibrant red curtain, symbolizing the presence of an aurora.

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

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

— NASA (@NASA) January 10, 2024

 

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.