Astronomers using NASA’s James Webb Space Telescope (JWST) have detected glowing aurorae akin to Earth’s northern and southern lights shining in the atmosphere of a brown dwarf located over 70 light years away, the space agency announced this week.
Brown dwarfs are mysterious celestial objects that are too large to be considered planets but failed to grow massive enough to ignite nuclear fusion in their cores and become stars. This newly studied free-floating brown dwarf, designated WISEA J153429.75-104303.3, is unusual because despite being isolated in space and having an atmospheric temperature of roughly 2500°F, it is exhibiting a phenomenon typically only seen around planets with magnetic fields like Earth, Jupiter and Saturn.
Magnetic Processes Generate Aurora on Rogue “Failed Star”
The aurorae on this brown dwarf, which astronomers have playfully nicknamed “The Loner”, are not being caused by energetic particles from a nearby star as they are in planetary aurorae within our solar system. Researchers believe complex magnetic processes in the high atmosphere layers of the brown dwarf are allowing charged particles to accelerate along magnetic field lines and collide with gases there to glow brightly.
“The occurrence of aurorae due to a brown dwarf’s magnetic activity is unprecedented,” said Kevin Luhman, an astronomer at Penn State University, in a press release. “It raises many new questions about how brown dwarfs generate magnetic fields and what causes those fields to be so strong.”
The discovery of an aurora glowing in infrared light around a seemingly inactive brown dwarf defies current theoretical models of brown dwarf atmospheres. These new findings reported in two papers in the journal Nature Astronomy are challenging astronomy’s understanding of magnetic processes and activity that naturally occur in brown dwarfs.
The NASA/ESA/CSA James Webb Space Telescope has revealed aurorae glowing on the brown dwarf WISEA J153429.75-104303.3 located over 70 light years away from Earth. (Image credit: NASA, ESA, CSA, Leah Hustak (STScI))
New Era of Brown Dwarf Exploration with JWST
The extremely sensitive JWST infrared camera instruments were able to tease out the faint signatures of auroral processes occurring in the lower pressure upper atmosphere layers of this rogue substellar dwarf.
“Observing the aurorae of our solar system planets is very challenging for astronomical telescopes because the light shows are predominantly seen in ultraviolet wavelengths,” explained Federico Marocco of the Korea Astronomy and Space Science Institute, lead author on one of the brown dwarf aurora studies. “However, the redder wavelengths towards the infrared permitted the Webb telescope to unveil for the first time auroral emissions at longer wavelengths.”
| Brown Dwarf Fact Sheet | |
|---|---|
| Age | Between 500 million and a few billion years old |
| Mass | 30-70 times more massive than Jupiter |
| Temperature | ~2500°F |
| Distance from Earth | Over 70 light years |
| Host star | Not orbiting a star, isolated “rogue” object |
The results of these studies signify an exciting new era of investigation into the weather, climate and poorly understood magnetism of small celestial bodies outside our solar system. Brown dwarfs, sometimes referred to as “failed stars”, are a class of cold substellar objects which have proven incredibly difficult to study in detail because they emit primarily in infrared wavelengths.
“These observations were only possible thanks to Webb’s unprecedented sensitivity at mid-infrared wavelengths where most brown dwarf aurorae shine,” said George Glasse of Johns Hopkins Applied Physics Laboratory, lead author of the other study about the brown dwarf aurora. “Because there are likely tens of billions of these lonely brown dwarfs roaming interstellar space, Webb may uncover more surprises as it continues exploring our ever-expanding galactic neighborhood.”
Aurora Linked to “Giant Convection Cell” Cloud Structures
Researchers were surprised to not only discover the telltale signatures of an aurora but also detect global-scale waves in the upper cloud layers of this small free-floating world. These never-before-seen atmospheric phenomena look similar to the cloud bands and vortices observed in images of Jupiter and Saturn captured by NASA’s Hubble Space Telescope and Juno and Cassini spacecraft. However, Jupiter-like fluid dynamics were not expected to be at play in such a relatively cool small body as WISEA J153429.75-104303.3.
Diagram depicting charged particles generating detectable auroral glows in upper layers of brown dwarf atmosphere. (Image credit: Leah Hustak (STScI))
The unveiling of this climate pattern is an indicator that massive planet-scale atmospheric convection cells are transporting heat on global scales within the brown dwarf. Researchers speculate these circulating gas motions combined with the intense magnetic field are somehow linked to acceleration of charged particles along magnetic field lines that collide with atmospheric gases at higher altitudes and result in auroral light emissions. Unraveling the root mechanisms causing the aurorae will be a high priority area of continued research.
“These observations clearly establish strong magnetic processes occur in some brown dwarfs, heating gas and accelerating charged particles that generate aurorae in their atmospheres,” shared Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate. “I am excited to see Webb push even deeper into the ultimate frontier, providing us insightful observations that no other observatory currently can.”
New Questions Raised About Brown Dwarf Magnetism
The discovery of infrared wavelength auroral activity in the light curve observations from the brown dwarf designated WISEA J153429.75-104303.3 has raised many new questions about the possible role of atmospheric circulation and weather in generating magnetism in brown dwarfs.
Some researchers speculate there may even be complex feedback mechanisms between global cloud dynamics, underlying atmospheric ionization processes, and high energy charged particles propagating along magnetic field lines that all interconnect in ways not accounted for in current dynamo theory models. Unraveling these mysteries and better understanding the self-perpetuating magnetic engine inside brown dwarfs will require much more observational data from JWST across myriad wavelengths.
“JWST has initiated a new era of clarifying and classifying different regimes of isolated substellar object magnetic behavior as more brown dwarfs are studied over time,” said Kevin Luhman, Penn State astronomer who leads an ongoing program to use JWST to study four enigmatic brown dwarfs. “Determining if there is an underlying magnetic phenomenon fundamentally unique to brown dwarfs is a top question raised by these initial results.”
Researchers will also be investigating if the brightness variations from aurorae processes on this brown dwarf could help explain some unusual near-infrared variability detected from coolest brown dwarfs with prior infrared astronomy spacecraft surveys. As the investigations into these phenomena continue, astronomers are hopeful the groundbreaking observations from JWST seen today are just the first of many paradigm-altering discoveries that will reshape our understanding of planetary atmosphere science outside our solar system.
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