Using the NASA/ESA/CSA James Webb Space Telescope with data from ESO's Very Large Telescope (VLT), two teams of astronomers captured mid-infrared images of a system of four serpentine spirals of dust around two aging Wolf-Rayet stars in a system known as Wow (2XMM J160050.7-514245).
Webb's mid-infrared image shows four dust shells coiled around a pair of Wolf-Rayet stars known as Apep. Image credit: NASA / ESA / CSA / STScI / Inuo Han, Caltech / Ryan White, Macquarie University / Alyssa Pagan, STScI
Wolf-Rayet stars are a rare class of massive binary stars that produce the earliest carbon in the Universe.
It is estimated that there are only a thousand in our Milky Way galaxy, which contains hundreds of billions of stars as a whole.
Of the several hundred binary Wolf-Rayet systems observed to date, the Apep system is the only example containing two Wolf-Rayet stars of these types in our Milky Way Galaxy.
In a new study, Macquarie University astronomer Ryan White and his colleagues sought to clarify the orbits of Wolf-Rayet stars in the Apep system.
They combined precise measurements of the rings' locations from the Webb image with the rate of expansion of the shells from eight years of VLT observations.
“This is the only system of its kind with an extremely long orbital period,” White said.
“The next longest orbit of the Wolf-Rayet dust binary is about 30 years. Most have orbits between two and 10 years.”
teams paper was simultaneously published in Astrophysical Journal with another paperCaltech astronomer
“Looking at Webb's new observations was like walking into a dark room and turning on the light—everything became clear,” Dr. Khan said.
“Webb's image shows dust everywhere, and the telescope shows that much of it has formed repeating, predictable patterns.”
Webb's observations provided the first image of its kind: a clear mid-infrared image of a system of four serpentine spirals of dust, one expanding after the other in exactly the same pattern. Ground-based telescopes detected only one shell before Webb discovered all four.
Webb's image, combined with several years of VLT data, narrowed down the frequency of how often the pair oscillates from each other: once every 190 years.
In each incredibly long orbit, stars pass close by for 25 years and form dust.
Webb's observations also confirmed that there are three stars in this system, gravitationally bound to each other.
The dust ejected by the two Wolf-Rayet stars is broken up by a third star, a massive supergiant that cuts a hole in each expanding dust cloud from its wider orbit.
“Webb gave us the smoking gun to prove that a third star is gravitationally bound to this system,” Dr Khan said.
Researchers have known about the third star since the VLT observed the brightest inner shell and stars in 2018, but Webb's observations led to an updated geometric model that confirmed the connection.
“We solved some mysteries with Webb,” Dr. Khan said.
“The remaining mystery is the exact distance of the stars from Earth, which will require future observations.”
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Ryan M.T. White etc.. 2025. The Snake Eating Its Tail: Dust Disruption in the Apep Headwind Nebula. APJ 994, 121; doi: 10.3847/1538-4357/adfbe1
Inuo Han etc.. 2025. JWST detects dust formation and evolution in the Apep binary system with crosswinds. APJ 994, 122; doi: 10.3847/1538-4357/ae12e5
