Astronomers utilizing NASA’s James Webb Space Telescope have identified a brown dwarf, named W1935, emitting infrared radiation from methane in its upper atmosphere. This discovery poses an intriguing mystery as W1935 is a cold brown dwarf without a host star, making the origin of energy in its upper atmosphere enigmatic. The research team speculates that the observed methane emission might be a result of processes generating aurorae, offering a novel perspective on the behavior of such celestial objects.
These unexpected findings are currently being presented at the 243rd meeting of the American Astronomical Society in New Orleans. To unravel the mystery, the astronomers draw parallels with our solar system, where methane emission linked to aurorae is a common feature in gas giants like Jupiter and Saturn.
Artist’s Concept of Brown Dwarf W1935.
This image’s concept depicts the enigmatic brown dwarf W1935, situated 47 light-years away from Earth. Recently discovered by astronomers using NASA’s James Webb Space Telescope, W1935 exhibits unexpected infrared emission from methane. The mystery deepens as this cold brown dwarf lacks a host star, leaving astronomers puzzled about the source of energy that heats its upper atmosphere, causing the methane to glow.
In this representation, the team speculates that the observed methane emission may be a result of processes generating aurorae, visually portrayed in vibrant red hues. This intriguing celestial illustration adds a new dimension to our understanding of these mysterious objects beyond our solar system.
Aurorae on Earth materialize when energetic particles from the Sun interact with our planet’s magnetic field, creating mesmerizing displays of light near the poles. Similarly, Jupiter and Saturn undergo auroral processes, influenced by their interaction with the solar wind and contributions from active moons like Io and Enceladus. However, the case of isolated brown dwarfs such as W1935 presents a puzzling challenge. Lacking a stellar wind to contribute to the auroral process, the mystery deepens regarding the additional energy needed for methane emission in the upper atmosphere.
The research team contemplates potential explanations, considering internal processes akin to Jupiter and Saturn’s atmospheric phenomena or external interactions with interstellar plasma or a nearby active moon to account for this intriguing emission. Unraveling this cosmic enigma promises to enhance our understanding of the diverse mechanisms at play in celestial bodies beyond our solar system.
The A Brown Dwarf Detective Story.
The aurorae’s discovery played out like a detective story. A team led by Jackie Faherty, an astronomer at the American Museum of Natural History in New York, was awarded time with the Webb telescope to investigate 12 cold brown dwarfs. Among those were W1935 – an object that was discovered by citizen scientist Dan Caselden, who worked with the Backyard Worlds zooniverse project – and W2220, an object that was discovered using NASA’s Wide Field Infrared Survey Explorer.
Webb revealed in exquisite detail that W1935 and W2220 appeared to be near clones of each other in composition. They also shared similar brightness, temperatures, and spectral features of water, ammonia, carbon monoxide, and carbon dioxide. The striking exception was that W1935 showed emission from methane, as opposed to the anticipated absorption feature that was observed toward W2220. This was seen at a distinct infrared wavelength to which Webb is uniquely sensitive.
The unexpected discovery of methane emission, instead of absorption, in brown dwarf W1935 prompted a sense of bewilderment among researchers, as described by Jackie Faherty, the lead astronomer on the project. Rather than adhering to the anticipated pattern of methane presence, the team observed a glow from this celestial object. Faherty recalled her initial reaction, questioning the unusual emission and pondering the reasons behind it. In their quest for answers, the team turned to computer models to discern the underlying factors influencing this phenomenon.
The models highlighted a stark difference between W2220 and W1935: while W2220 displayed the anticipated cooling with increasing altitude, W1935 exhibited a surprising temperature inversion, where the atmosphere warmed with higher altitudes. This unexpected temperature inversion adds an intriguing layer to the mystery, especially considering the absence of an apparent external heat source for W1935. Lead modeler Ben Burningham from the University of Hertfordshire expressed the astonishment of witnessing such a phenomenon in an object devoid of an obvious external heat influence, describing it as a truly remarkable revelation.
Spectra W1935 vs W2220.
Leveraging the capabilities of NASA’s James Webb Space Telescope, astronomers embarked on a study of 12 cold brown dwarfs, leading to a fascinating revelation. Among these celestial objects, W1935 and W2220 emerged as almost identical twins in terms of composition, brightness, and temperature. However, the intriguing twist surfaced when W1935 exhibited methane emission, contrary to the anticipated absorption feature observed in W2220.
This unexpected difference has prompted the research team to speculate that the methane emission in W1935 may be a result of processes generating aurorae, adding a new layer to our understanding of these enigmatic objects beyond our solar system.
Solar System Insights Illuminate Brown Dwarf Mystery.
Drawing inspiration from our solar system, the research team sought clues closer to home, examining the atmospheric dynamics of the gas giant planets. Recognizing that these planets can offer insights into what occurs over 40 light-years away in the atmosphere of W1935, the team focused on the temperature inversions observed in planets like Jupiter and Saturn.
While ongoing research aims to unravel the causes of stratospheric heating in these planets, leading theories in our solar system involve external heating through aurorae and internal energy transport from deeper layers of the atmosphere, with the former standing out as a prominent explanation. This comparative analysis sheds light on potential parallels between our nearby planets and the intriguing brown dwarf W1935, contributing to the ongoing cosmic detective work.
Understanding Brown Dwarf Aurora Candidates in a Cosmic Context.
The notion of aurorae explaining brown dwarf observations isn’t novel, as astronomers have previously detected radio emission from warmer brown dwarfs, attributing it to auroral processes. Earlier searches using ground-based telescopes like the Keck Observatory aimed to uncover infrared signatures accompanying the radio-emitting brown dwarfs to enhance understanding, but these efforts yielded inconclusive results. However, W1935 marks a significant breakthrough as the first auroral candidate beyond our solar system exhibiting the signature methane emission.
Distinguished as the coldest auroral candidate outside our solar system, W1935 boasts an effective temperature of approximately 400 degrees Fahrenheit (200 degrees Celsius), making it about 600 degrees Fahrenheit warmer than Jupiter. This discovery opens new avenues for exploring the intricacies of aurorae beyond our celestial neighborhood.
Unlike our solar system, where the solar wind significantly contributes to auroral processes and active moons like Io and Enceladus influence aurorae on Jupiter and Saturn, W1935 presents a unique scenario. Devoid of a companion star, W1935 lacks a stellar wind that could contribute to the observed phenomenon. The absence of a stellar companion raises intriguing questions about the potential role of an active moon in the methane emission on W1935, a query yet to be fully explored.
Jackie Faherty emphasized the significance of this discovery, stating, “With W1935, we now have a spectacular extension of a solar system phenomenon without any stellar irradiation to help in the explanation.” The advanced capabilities of the James Webb Space Telescope (Webb) offer a promising opportunity to delve deeper into the chemistry of W1935’s auroral process, unraveling the similarities or distinctions in these cosmic phenomena beyond our solar system. Faherty highlighted Webb’s potential, stating, “With Webb, we can really ‘open the hood’ on the chemistry and unpack how similar or different the auroral process may be beyond our solar system.” This exploration promises to shed light on the intricate celestial processes at play in this distant brown dwarf.