Using NASA/ESA/CSA’s James Webb Space Telescope, astronomers detected a brown dwarf with infrared emissions from methane, likely due to energy in the upper atmosphere. The heating of the upper atmosphere that drives this emission is associated with auroras. The brown dwarf, named W1935, is located 47 light-years away.
Artist’s impression of the brown dwarf W1935. Image credit: NASA/ESA/CSA/L. Hustak, STScI.
On Earth, auroras occur when energetic particles blasted into space from the sun are captured by Earth’s magnetic field.
They cascade into the atmosphere along magnetic field lines near the Earth’s poles, colliding with gas molecules and creating eerie, dancing curtains of light.
Jupiter and Saturn have similar auroral processes that involve interaction with the solar wind, but also receive auroral contributions from nearby active moons, such as Io (for Jupiter) and Enceladus (for Saturn). Masu.
“For an isolated brown dwarf like W1935, the absence of a stellar wind that contributes to auroral processes and accounts for the extra energy in the upper atmosphere required for methane emission is puzzling,” American Airlines astronomers said. said Dr. Jackie Faherty. Natural History Museum and colleagues.
Faherty and his colleagues used Webb to observe a sample of 12 cool brown dwarf stars.
These included object W1935, discovered by citizen scientist Dan Caselden who collaborated on the Backyard Worlds Zooniverse project, and object W2220, discovered using NASA’s Wide Field Infrared Survey Explorer.
Webb revealed in great detail that W1935 and W2220 appear to be close clones of each other in composition.
Also, the brightness, temperature, and spectral characteristics of water, ammonia, carbon monoxide, and carbon dioxide were similar.
A notable exception is that W1935 showed emission from methane, in contrast to the expected absorption feature observed for W2220. This was observed at infrared wavelengths, to which Webb is uniquely sensitive.
“We expected methane to be present because it’s everywhere in these brown dwarfs,” Faherty said.
“But instead of absorbing light, we found just the opposite. The methane was glowing. My first thought was, what the hell? Why is this object emitting methane?” Do you want it?
Astronomers used computer models to deduce what might be behind the emission.
Modeling work showed that W2220 has a predictable energy distribution in its atmosphere, becoming colder with increasing altitude.
On the other hand, W1935 produced surprising results. The best models supported a temperature inversion, where the atmosphere becomes warmer as altitude increases.
“This temperature inversion is really puzzling,” says Dr. Ben Burningham, an astronomer at the University of Hertfordshire.
“We’ve seen this kind of phenomenon on planets with nearby stars that can heat the stratosphere, but it’s outrageous to see something like this on a celestial body with no obvious external heat source. .
In search of clues, researchers looked to our backyard: the planets of our solar system.
The gas giant planet could serve as a proxy for what is seen happening 47 light-years away in the atmosphere of 1935 AD.
Scientists have noticed that planets like Jupiter and Saturn have significant temperature inversions.
Research is still ongoing to understand the causes of stratospheric heating, but leading theories about the solar system include external heating by auroras and internal energy transport from deep in the atmosphere, with the former being the leading explanation. ).
According to the research team, W1935 is the first aurora candidate outside the solar system with the signature of methane emission.
It is also the coldest aurora candidate outside the solar system, with an effective temperature of about 200 degrees Celsius (400 degrees Fahrenheit).
In our solar system, the solar wind is the main contributor to the auroral process, and active satellites like Io and Enceladus play the role of planets like Jupiter and Saturn, respectively.
W1935 does not have any companion stars, so stellar winds cannot contribute to this phenomenon. It is not yet known whether an active moon is responsible for her W1935's methane emissions.
“W1935 provides a spectacular expansion of solar system phenomena without any explanatory stellar illumination,” Faherty said.
“With Webb, we can actually ‘lift the lid’ on chemistry and figure out how auroral processes are similar or different outside of our solar system.”
The authors announced that findings this week’s AAS243243rd Meeting of the American Astronomical Society, New Orleans, USA.
_____
Jacqueline Faherty other. 2024. JWST exhibits the auroral features of frigid brown dwarfs. AAS243Abstract #4359
