NASA’s James Webb Space Telescope has given astronomers a new view of a system of strange dust spirals in space generated by two ageing stars.
Webb's infrared image captured an image of the four spirals of dust, revealing there's more to this strange system than astronomers had originally expected.
A system of chaos
This whirling system of space dust is known as Apep, after the Egyptian god of chaos, and was formed over the last 700 years by two ageing stars known as Wolf-Rayet stars.
Wolf-Rayet stars are rare, with only 1,000 thought to exist in our entire Galaxy.
These two stars are orbiting one another, and each time they approach and swing by each other, their stellar winds collide, forming huge discs of cosmic dust over the space of a quarter of a century.
More from Webb
Previous observations of Apep had only detected one shell, but the James Webb Space Telescope has revealed four.
Webb's data was combined with previous data from the European Southern Observatory’s Very Large Telescope in Chile.
The two observatories revealed that the pair of stars swing past one another every 90 years, taking 25 years to do so and forming the dusty spirals in their wake.
An unexpected surprise
Webb has also confirmed there are actually three stars in this system. The dust ejected by the two Wolf-Rayet stars is slashed by a third massive supergiant star.
This third star has a wider orbit and carves holes in the expanding dust clouds. All three stars appear as a single bright point of light in Webb’s image.
"Looking at Webb’s new observations was like walking into a dark room and switching on the light – everything came into view," says Yinuo Han, lead author of the study and postdoctoral researcher at Caltech in Pasadena, California.
"There is dust everywhere in Webb’s image, and the telescope shows that most of it was cast off in repetitive, predictable structures."
Another paper on the discovery was released by Ryan White, a PhD student at Macquarie University in Sydney, Australia.
The astronomers were able to refine the Wolf-Rayet stars’ orbits by measuring the locations of the ring location and comparing it with the speed of the dusty shells’ expansion.
"This is a one-of-a-kind system with an incredibly rare orbital period," says White.
"The next longest orbit for a dusty Wolf-Rayet binary is about 30 years. Most have orbits between two and 10 years."
Looking for the dust slicer
The Wolf-Rayet stars in Apep emit dust into space at 2,000 to 3,000 km per second (1,200 to 2,000 miles per second).
And Webb's infrared vision was able to give astronomers a view of the system like never before.
The light these dust grains emit is very faint, so could only be detected by Webb’s MIRI (Mid-Infrared Instrument).
You can see the slice in the dust caused by the third star by looking at the central bright point in Webb's image, then tracing a faint V shape from the 10 o'clock to the 2 o'clock mark.
"The cavity is more or less in the same place in each shell and looks like a funnel," says White. "I was shocked when I saw the updated calculations play out in our simulations.
"Webb gave us the ‘smoking gun’ to prove the third star is gravitationally bound to this system.
"We solved several mysteries with Webb. The remaining mystery is the precise distance to the stars from Earth, which will require future observations."
The future of the Apep system
The two Wolf-Rayet stars are thought to be about 10–20 times the mass of our Sun, but were once much bigger.
All that dust-shedding has led to them shrinking in size. For comparison, they used to be more massive than the third red giant, which is about 40–50 times as massive as the Sun.
Scientists say the Wolf-Rayet stars will eventually end their lives in a supernova explosion, and either may even become a black hole.
