Webb Spots Shells of Carbon-Rich Dust around Wolf-Rayet 140 | Sci.News
Wolf-Rayet 140 (also known as WR 140 or HD 193793) is a system of two massive stars located some 5,000 light-years away in the constellation of Cygnus. As these stars swing past one another, the stellar winds from each star slam together, the material compresses, and carbon-rich dust forms. The new observations from the NASA/ESA/CSA James Webb Space Telescope show 17 dust shells shining in mid-infrared light that are expanding at regular intervals into the surrounding space.
This image of the carbon-rich Wolf-Rayet star WR 140 was captured by Webb’s Mid-Infrared Instrument (MIRI) in September 2023. Image credit: NASA / ESA / CSA / STScI / E. Lieb, University of Denver / R. Lau, NSF’s NOIRLab / J. Hoffman, University of Denver.
“Webb confirmed that Wolf-Rayet 140’s dust shells are real, and its data also showed that the dust shells are moving outward at consistent velocities, revealing visible changes over incredibly short periods of time,” said Emma Lieb, a doctoral student at the University of Denver in Colorado.
“Every shell is racing away from the stars at more than 2,600 km per second, almost 1% the speed of light.”
“We are used to thinking about events in space taking place slowly, over millions or billions of years,” said University of Denver’s Professor Jennifer Hoffman.
“In this system, the observatory is showing that the dust shells are expanding from one year to the next.”
“Seeing the real-time movement of these shells between Webb’s observations that were taken only 13 months apart is truly remarkable,” said Dr. Olivia Jones, an astronomer at the UK Astronomy Technology Centre.
“These new results are giving us a first glimpse of the potential role of such massive binaries as factories of dust in the Universe.”
Like clockwork, the stars’ winds generate dust for several months every eight years, as the pair make their closest approach during a wide, elongated orbit.
Webb also shows where dust formation stops — look for the darker region at top left in the image.
The telescope’s mid-infrared images detected shells that have persisted for more than 130 years — older shells have dissipated enough that they are now too dim to detect.
The astronomers speculate that the stars will ultimately generate tens of thousands of dust shells over hundreds of thousands of years.
“Mid-infrared observations are absolutely crucial for this analysis, since the dust in this system is fairly cool,” said Dr. Ryan Lau, an astronomer at NSF’s NOIRLab.
“Near-infrared and visible-light observations would only show the shells that are closest to the star.”
“With these incredible new details, the telescope is also allowing us to study exactly when the stars are forming dust — almost to the day.”
The distribution of the dust isn’t uniform. Though these differences aren’t obvious in Webb images, the researchers found that some of the dust has ‘piled up,’ forming amorphous, delicate clouds that are as large as our entire Solar System.
Many other individual dust particles float freely. Every speck is as small as one-hundredth the width of a human hair. Clumpy or not, all of the dust moves at the same speed and is carbon rich.
What will happen to these stars over millions or billions of years, after they have finished ‘spraying’ their surroundings with dust?
The Wolf-Rayet star in this system is 10 times more massive than the Sun and nearing the end of its life.
In its final ‘act,’ this star will either explode as a supernova — possibly blasting away some or all of the dust shells — or collapse into a black hole, which would leave the dust shells intact.
Though no one can predict with any certainty what will happen, the scientists are rooting for the black hole scenario.
“A major question in astronomy is, where does all the dust in the Universe come from?” Dr. Lau said.
“If carbon-rich dust like this survives, it could help us begin to answer that question.”
“We know carbon is necessary for the formation of rocky planets and solar systems like ours,” Professor Hoffman said.
“It’s exciting to get a glimpse into how binary star systems not only create carbon-rich dust, but also propel it into our galactic neighborhood.”
The findings were published in the Astrophysical Journal Letters.
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Emma P. Lieb et al. 2025. Dynamic Imprints of Colliding-wind Dust Formation from WR 140. ApJL 979, L3; doi: 10.3847/2041-8213/ad9aa9
