JWST’s mid-infrared image of the spiraling dust shells around the triple star system Apep, which includes two Wolf-Rayet stars. (Image credit: NASA/ESA/CSA/STScI; Science: Yinuo Han (Caltech)/Ryan White (Macquarie University); Image Processing: Alyssa Pagan (STScI).)

A nested series of dusty spirals is captured swirling around a mighty triple star system containing two of the rarest stars in the galaxy in a new image from NASA’s James Webb Space Telescope (JWST).

The triple system is nicknamed Apep, after the Egyptian god of chaos, and cosmic chaos. It’s on dramatic display in JWST’s new mid-infrared image, which makes the object look like an immense cosmic embryo. Two of the stars in Apep are Wolf-Rayet stars, which are massive and extremely hot stars that live a life bordering on instability, with powerful stellar winds carrying huge clumps of material from them, exposing a helium-, nitrogen- and carbon-rich interior. Only about 1,000 Wolf-Rayet stars are known in our Milky Way galaxy, among more than 100 billion other stars.

The material removed by the winds — not winds as we know them on Earth, but streams of charged particles — forms a nebula, and when a Wolf-Rayet star exists in a binary system with another star, the gravitational interactions between the two can sculpt the shape of that nebula. Apep, however, is unique as far as we know in that it features two Wolf-Rayet stars revolving around one another on a 190-year orbit. At closest approach, their stellar winds collide, producing dense, carbon-rich dust that forms a spiral shape over the course of 25 years each time. Each spiral then begins the journey of expanding outwards.

“This is a one-of-a-kind system with an incredibly rare orbital period,” said Ryan White, a Ph.D. student at Macquarie University in Sydney, Australia, in a statement. “The next longest orbit for a dusty Wolf-Rayet binary is about 30 years. Most have orbits between two and 10 years.”

When Apep was discovered in optical light in 2018 by the European Southern Observatory’s Very Large Telescope in Chile, only the brightest, innermost spiral was visible, but more were suspected to exist. JWST’s Mid-Infrared Instrument (MIRI) has now captured them, nested inside one another and representing four close approaches of the stars over the past 700 years or so. The outermost spiral is the faintest, on the periphery of JWST’s vision.

“Looking at Webb’s new observations was like walking into a dark room and switching on the light — everything came into view,” said Yinuo Han of the California Institute of Technology in Pasadena, who is the lead author of one paper describing the observations, while White is lead author of another. “There is dust everywhere in Webb’s image, and the telescope shows that most of it was cast off in repetitive, predictable structures.”

White’s study refined the orbits of Apep’s stars by combining the JWST data with eight years’ worth of observations by the Very Large Telescope that chart the expansion of the innermost dusty shell.

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Remarkably, the images betray the presence of a third star, even more massive than the two Wolf-Rayet stars. In both the Very Large Telescope’s and JWST’s images, the triple star system is unresolved, looking like a single star at Apep’s distance of roughly 8,000 light-years, although their exact distance is a continuing mystery.

A compass image showing the size of Apep’s dust shells, and the funnel shape of the cavity carved by a third star. (Image credit: NASA/ESA/CSA/STScI; Science: Yinuo Han (Caltech)/Ryan White (Macquarie University); Image Processing: Alyssa Pagan (STScI).)

While the Wolf-Rayet stars have masses between 10 and 20 times that of our sun, their triple companion is a supergiant between 40 and 50 times as massive as the sun. Its presence is revealed through the way it interacts with the stellar winds and dust from the Wolf-Rayet stars, leaving a cavity in the expanding, spiraling shells. This gap is best seen between the 10 o’clock and 2 o’clock positions in the JWST image.

“The cavity is more or less in the same place in each shell and looks like a funnel,” said White.

All three stars are destined to explode as a supernova, the two Wolf-Rayet stars possibly going boom as gamma-ray bursts leaving behind stellar-mass black holes that will be orbited by a neutron star left behind when the more massive supergiant explodes.

Both papers were published Wednesday (Nov. 19) in The Astrophysical Journal, with Han’s paper found here and White’s paper here.

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He’s the author of “The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence” (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.