Webb telescope discovers a new surprise about a rare pair of extreme stars

NASA's James Webb Space Telescope has revealed that an exceptionally rare star duo in the Milky Way has a third companion — and it's a monster.

The star system, named Apep after the Egyptian god of chaos, includes two Wolf-Rayet stars, a type that burns blue-white and hot, generating powerful gas winds as it nears death. These stars are old, huge, and on the verge of supernova explosions. 

The Apep pair has intrigued astronomers because of how scarce Wolf-Rayet stars are in space. Only about 1,000 exist in the galaxy, which contains hundreds of billions of stars. Of the few binary star systems involving Wolf-Rayets, Apep is the only one wherein both fall in this category. 

Now new telescope studies confirm that Apep has a third star — a supergiant roughly 40 or 50 times more massive than the sun. The two Wolf-Rayet stars were likely even heavier than that when they were younger, but have since shriveled down to 10 and 20 times the mass of our host star. 

"Webb gave us the 'smoking gun' to prove the third star is gravitationally bound to this system,'" said Ryan White, a lead author from Macquarie University in Australia, in a statement. 

With Webb, astronomers were able to see the two Wolf–Rayet stars blasting out fierce winds that smash together and make carbon dust. Instead of one big cloud, Apep has a stack of four nested dust shells that look like the ripples surrounding a stone plopped into a pond. Each shell repeats the same pattern, indicating the dust-making process fires on a steady rhythm.

The shells hold their shape even as they drift nearly two light-years outward. But despite their predictability, the shells aren't perfectly round. Slight warps probably come from the stars' long, stretched orbit, according to the research, or from winds that blow harder in some directions than others.

The James Webb Space Telescope revealed neat, layered dust shells shaped by two powerful stars. Credit: NASA GSFC / CIL / Adriana Manrique Gutierrez illustration

The findings are described in two new papers published in The Astrophysical Journal. 

"Looking at Webb’s new observations was like walking into a dark room and switching on the light," said Yinuo Han, lead author of one of the papers, in a statement. "Everything came into view." 

The shells formed over the last 700 years as the two stars repeatedly approached each other. Their gas collisions shoot out thick clumps of carbon dust at 1,200 to 2,000 miles per second. By measuring how fast the shells move and how far apart they sit, researchers estimate that the two orbit each other about once every 193 years. 

As for the third star, it circles around the other two from a wider distance. As the dust shells expand, this outer star plows through them, leaving a neat, pie-shaped gap in every shell. Because the gap appears in the same place each time, researchers know it's part of the system.

The dust temperatures, shell spacing, and the system’s overall brightness point to Apep being farther away than earlier studies suggested — perhaps 15,000 light-years off in the distance.

"We solved several mysteries with Webb," Han said. "The remaining mystery is the precise distance to the stars from Earth, which will require future observations."