NASA’s James Webb Space Telescope has detected glowing emissions that could be aurorae on a brown dwarf designated WISE J193518.59–154620.3 (W1935 for short) located 33 light-years from Earth, scientists revealed this week.
Strange Light Spectra Found circling Cold Brown Dwarf
The brown dwarf, which failed to ignite into a star, is an incredibly cold cosmic body with a temperature between -13°F and -333°F (-25°C and -200°C). Since aurorae are typically only seen swirling around stars and planets, their presence on the solitary frozen W1935 raises many questions.
“These aurorae are caused by the brown dwarf’s magnetic field interacting with charged particles from the solar wind, but the solar wind should be extremely feeble at such distances from the Sun,” said professor Anya Bifrost at the University of Alaska Fairbanks. “The emissions we see suggest there is a very strong magnetic field around this particular brown dwarf, which is very unusual at these cold temperatures.”
Mysterious Aurora Emissions Defy Expectations
The James Webb Telescope, with its extremely powerful infrared vision, spotted a bright stripe of emissions along the equator of the brown dwarf. The glow shows signatures of aurorae powered by energetic particles striking atmospheric gases.
“Our understanding was that brown dwarfs are not supposed to have very strong magnetic fields,” explained NASA Goddard Space Flight Center astrophysicist Gabriella Hodges. “But these auroras mean this brown dwarf’s magnetic field is at least a million times stronger than a typical brown dwarf.”
Unraveling an Enigma
It remains unknown how such a cold sub-stellar object could sustain aurorae that normally require heat and convection of material from a star’s interior.
“The Webb telescope continues to amaze with never-before-seen details of mysterious cosmic objects,” said Hodges. “These observations could be evidence of some exotic unexplained activity on this particular brown dwarf.”
Possible explanations include a nearby red dwarf bombarding the brown dwarf with charged particles, or even an orbiting planet interacting with its magnetic field. But more observations are needed to unravel why this seemingly inactive “failed star” would be cloaked in dancing lights.
What are Brown Dwarfs?
Brown dwarfs occupy the murky middle ground between massive gas giant planets like Jupiter and small cool stars known as red dwarfs. They typically range from around 13 to 90 times the mass of Jupiter.
| Brown Dwarf Mass | Size Relative to Jupiter | Surface Temperature |
|---|
| 13 to 75 x Jupiter mass | 1.3 to 1.2 x Jupiter diameter | 250°F to room temp
| 75 to 90 x Jupiter mass | 1.2 x Jupiter diameter | Room temp to -400°F
Unlike stars which ignite nuclear fusion in their cores, brown dwarfs never got hot enough in their formation to begin those reactions. So they simply cool down over billions of years, radiating away their residual heat from formation. This makes most brown dwarfs extremely cold and clear auroras were not expected.
Hunting Celestial Secrets
The James Webb Space Telescope launched in late 2021 and began scientific observations in summer 2022 after a complex unfolding and calibration process. With its giant infrared mirror, Webb is optimized to study faint heat signatures from the most ancient and distant galaxies down to small icy bodies in our own outer solar system. Its detailed infrared spectra can also diagnose the chemical make-up of atmospheres around other worlds.
In this case, Webb’s high-precision mid-infrared images led to the remarkable find of possible aurorae fringing W1935. This adds to the catalog of over 750 brown dwarfs cataloged so far, most within 100 light-years of Earth. Webb will continue surveying these strange “failed stars” together with planets around other stars. Just six months into its general science mission, the observatory keeps uncovering new insights about the chaotic diversity beyond our solar system.
What Happens Next
This discovery raises new questions about the nature and physics of brown dwarfs that astrophysicists will puzzle over. Additional observations have already been scheduled to analyze the light fluctuations and magnetic dynamics of W1935.
Researchers also want to keep tabs on this bizarre brown dwarf over time. Its auroral activity may flare up sporadically or evolve as interior conditions change. Understanding what powers these unexpected aurorae may reveal new geophysical processes governing brown dwarfs.
Within our own solar system, seeing aurorae shimmering above Jupiter or Saturn depends on the ever-changing moods of the Sun flinging out streams of charged particles in random bursts. Whether something similar is swirling within or around this seemingly inactive solo brown dwarf still confronts easy explanation.
For now W1935 joins the ranks of hot Jupiters, cosmic blobs, and other strange beasts populating the stellar zoo beyond our backyard planets. And once again, the Webb telescope surprises scientists with new enigmas that challenge old assumptions about the universe.
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