Webb Watches Carbon-Rich Dust Shells Form, Expand in Star System

NASA · January 13

6 Min Read

Webb Watches Carbon-Rich Dust Shells Form, Expand in Star System

A portion of Webb’s 2023 observation of Wolf-Rayet 140.

Credits:
Image: NASA, ESA, CSA, STScI; Science: Emma Lieb (University of Denver), Ryan Lau (NSF NOIRLab), Jennifer Hoffman (University of Denver)

Astronomers have long tried to track down how elements like carbon, which is essential for life, become widely distributed across the universe. Now, NASA’s James Webb Space Telescope has examined one ongoing source of carbon-rich dust in our own Milky Way galaxy in greater detail: Wolf-Rayet 140, a system of two massive stars that follow a tight, elongated orbit.

As they swing past one another (within the central white dot in the Webb images), the stellar winds from each star slam together, the material compresses, and carbon-rich dust forms. Webb’s latest observations show 17 dust shells shining in mid-infrared light that are expanding at regular intervals into the surrounding space.

Image A: Compare Observations of Wolf-Rayet 140 (MIRI Images)

A three-part graphic. The left and center images show two observations of Wolf-Rayet 140, from July 2022 at left and from September 2023 at center. Both show a bright white point of light surrounded by 17 regularly spaced, hazy dust shells at the bottom, right, and upper right. The panels each have an outline of a square overlaid toward the top right, which has a brighter white outline of a triangle. At left, the triangle points up and is labeled a. At right, the triangle points down and is labeled b. The third panel at right shows a magnified version of the areas outlined in the left and center panels. There are two labels. At top left, a, and at bottom right, b. It is very obvious that the arced orange shells do not perfectly match in the middle where they are spliced together. The arcs at left appear lower, and the arcs at right all appear higher. Each arc lines up for about half its width.

Two mid-infrared images from NASA’s James Webb Space Telescope of Wolf-Rayet 140 show carbon-rich dust moving in space. At right, the two triangles from the main images are matched up to show how much difference 14 months makes: The dust is racing away from the central stars at almost 1% the speed of light. These stars are 5,000 light-years away in our own Milky Way galaxy.

Image: NASA, ESA, CSA, STScI; Science: Emma Lieb (University of Denver), Ryan Lau (NSF NOIRLab), Jennifer Hoffman (University of Denver)

“The telescope not only confirmed that these dust shells are real, 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, the lead author of the new paper and a doctoral student at the University of Denver in Colorado.

Every shell is racing away from the stars at more than 1,600 miles per second (2,600 kilometers 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,” added Jennifer Hoffman, a co-author and a professor at the University of Denver. “In this system, the observatory is showing that the dust shells are expanding from one year to the next.”

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 how dust formation varies — look for the darker region at top left in both images.

Video A: Fade Between 2022 and 2023 Observations of Wolf-Rayet 140

The video alternates between two James Webb Space Telescope images of the two-star system Wolf-Rayet 140, the first taken in 2022 and the second in 2023. Both show a bright white point of light surrounded by 17 regularly spaced, hazy dust shells at the bottom, right, and upper right. There is noticeably less color in the upper left. The central point, where the two stars are located, has a rough hexagon shape. By alternating between them, it’s clear that the dust shells are moving outward, becoming wider.

This video alternates between two mid-infrared light observations from NASA’s James Webb Space Telescope of Wolf-Rayet 140. Over only 14 months, Webb showed the dust in the system has expanded. This two-star system has sent out more than 17 shells of dust over 130 years.

Video: NASA, ESA, CSA, STScI.; Science: Emma Lieb (University of Denver), Ryan Lau (NSF NOIRLab), Jennifer Hoffman (University of Denver)

Video B: Stars’ Orbits in Wolf-Rayet 140 (Visualization)

When the two massive stars in Wolf-Rayet 140 swing past one another, their winds collide, material compresses, and carbon-rich dust forms. The stronger winds of the hotter star in the Wolf-Rayet system blow behind its slightly cooler (but still hot) companion. The stars create dust for several months in every eight-year orbit.
Video: NASA, ESA, CSA, Joseph Olmsted (STScI).

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 researchers 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. Near-infrared and visible light would only show the shells that are closest to the star,” explained Ryan Lau, a co-author and astronomer at NSF NOIRLab in Tuscon, Arizona, who led the initial research about this system. “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 dust’s distribution isn’t uniform. Though this isn’t obvious at first glance, zooming in on the shells in Webb’s images reveals 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.

The Future of This System

What will happen to these stars over millions or billions of years, after they are 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, researchers are rooting for the black hole scenario. “A major question in astronomy is, where does all the dust in the universe come from?” 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,” Hoffman added. “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.”

These results have been published in the Astrophysical Journal Letters and were presented in a press conference at the 245th meeting of the American Astronomical Society in National Harbor, Maryland.

The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.