Webb Telescope Watches Rippling Dust Shells – Sky & Telescope

Posted on 16/01/2025

A three-part graphic showing observations of Wolf-Rayet 140, two massive stars with 17 dust shells around them. An inset appears at right, showing a portion of the two observations matched up to show that the arced dust has moved. — Comparison of two mid-infrared images taken by the James Webb Space Telescope. At center is Wolf-Rayet 140, two massive stars in elongated mutual orbits. Their interactions have ejected a system of dust shells, which have expanded over time, as shown in observations taken in 2022 (left) and 2023 (center). The expansion is clearest in the comparison shown at right.
*NASA / ESA / CSA / STScI / E. Lieb (University of Denver) / R. Lau (NSF NOIRLab) / J. Hoffman (University of Denver)*

Multiple James Webb Space Telescope observations have shed new light on dust-forming activity around an extreme stellar duo some 5,000 light-years away in the Milky Way.

The pair are both massive stars, one of them a blue-white O star and the other a brilliant Wolf-Rayet star that has run out of hydrogen to fuse in its core. Both stars are pushing away their outermost layers in strong stellar winds, but the Wolf-Rayet’s winds are really going gangbusters. The stars are caught in a mutual orbit, swinging close to each other every eight years. When they do, their strong winds collide.

When the two massive stars in Wolf-Rayet 140 swing past each other every eight years, their winds collide. Dust forms for several months afterward. The stronger winds of the hotter Wolf-Rayet star blow behind its slightly cooler O-star companion.
NASA / ESA / CSA / J. Olmsted (STScI)

In the aftermath of each close approach, compressed gas is flung outward in a spiral where, cooling, it forms dust. Every eight years, another round is added to the spiral shape, with more than a dozen shells visible with Webb imagery. The telescope has been watching these dusty rings expand since 2022, and the resulting “movie” of their expansion over time is now out:

This video alternates between two James Webb Space Telescope observations of Wolf-Rayet 140, taken at mid-infrared wavelengths in 2022 and in 2023. Blinking between the observations showcases the shells’ movements over a year’s time. (Note that bright stars in the image are surrounded by diffraction spikes; these are artifacts and not real.)

By following the expansion of the dusty shells, Emma Lieb (University of Denver) announced at the 245th meeting of the American Astronomical Society in Washington, D.C., that the material is expanding at 2,700 kilometers per second — that’s more than 1% the speed of light.

“These shells are moving at a real clip!” Lieb said at the press conference on January 13th. She added, however, that the speed is entirely expected, based on the speed of the stellar wind coming from the more massive star.

The images are sharp enough to show clumpiness within the shells. Researchers could use these observations to test ideas of dust formation in such highly irradiated environments. The results presented at the conference also appear in the January 20th Astrophysical Journal Letters.

Article by:Source – Monica Young