In July, a new image of a distant extreme star system surrounded by unreal concentric geometric notches left astronomers scratching their heads. The photo, which looks like a sort of “cosmic thumbprint,” comes from NASA’s latest flagship observatory, the James Webb Space Telescope.
The internet was immediately ablaze with theories and speculation. Some on the Wild Shore also claimed it as evidence of an “alien megastructure” of unknown origin.
Fortunately, our team at the University of Sydney had already been studying this star, known as WR140, for more than 20 years – so it was time to use physics to explain what we were seeing. We were in a prime position for that.
Our model, published in Nature, explains the strange process by which the star produces the luminous pattern of rings seen in the Webb image (itself now published in Nature Astronomy).
WR140 . the secrets
WR140 is called Wolff-Rayet star. These are among the most extreme stars known. In a rare but beautiful display, they can sometimes emit dust plumes into space that are hundreds of times the size of our entire solar system.
The radiation field around Wolf-Rayets is so intense, dust and air are swept outward at thousands of kilometers per second, or about 1 percent of the speed of light. While all stars have stellar winds, these supergiants drive something more like stellar storms.
Crucially, this air contains elements such as carbon that precipitate out to form dust.
WR140 is one of the few dusty Wolf-Rayet stars found in a binary system. It is in orbit with another star, a massive blue supergiant with a ferocious air of its own.
Only a few systems like WR140 are known throughout our galaxy, yet they offer the most unexpected and beautiful gifts to a select few astronomers. The dust doesn’t just fly out of the star to form a hazy ball, as expected; Instead it forms only in a cone-shaped region where the winds of the two stars collide.
Because the binary star is in constant orbital motion, this shock front must rotate as well. The sooty plums are then naturally wrapped in a spiral, similar to the jets from a revolving garden sprinkler.
The WR140, however, has a few more tricks up its sleeve while wielding more rich complexity in its showy display. The two stars are in elliptical orbits, not circular, and in addition, dust production turns on and off episodically as the binary nears and departs from the point of closest approach.
almost a perfect model
By modeling all of these effects in the three-dimensional geometry of the dust plume, our team tracked the location of dust features in three-dimensional space.
By carefully tagging images of the expanding flow taken at the Keck Observatory, one of the world’s largest optical telescopes, we found that our model of the expanding flow fit the data almost perfectly.
Except for a ghazal. Right near the star, the dust was not where it should have been. Chasing down that minor misfit led us to an incident that had never been caught on camera before.
power of light
We know that light has momentum, which means it can exert a force on a substance called radiation pressure. The result of this phenomenon, in the form of beach-bound matter accelerating around the universe, is evident everywhere.
But it has been a remarkably difficult process to get caught in the act. The force fades quickly with distance, so to see the material being accelerated you need to very accurately track the motion of matter in a strong radiation field.
This acceleration turned out to be a missing element in the WR140’s model. Our data didn’t fit because the expansion speed was not constant: the dust was being promoted by radiation pressure.
Capturing it on camera for the first time was something new. In each orbit, it is as if the star hoists a giant sail made of dust. When it catches the rapid radiation flux from the star, like a yacht catches a gust, the dusty sail suddenly leaps forward.
smoke rings in space
The end result of all this physics is amazingly beautiful. Like a clockwork toy, the WR140 puts out precisely sculpted smoke rings every eight years of orbit.
Each ring is carved out of all this wonderful physics written in the detail of its form. All we have to do is wait and the expanding air inflates the dust ball like a balloon until it is big enough for our telescopes to image.
Then, eight years later, the binary returns to its orbit and the second shell appears similar to the first, growing inside the bubble of its predecessor. The shells keep piling up like a ghostly set of giant nesting dolls.
However, the extent to which we hit upon the correct geometry to explain this intriguing star system wasn’t brought home to us until the new Webb image arrived in June.
There were not one or two, but more than 17 exquisitely sculpted spheres, each an almost exact replica contained within the one before it.
This means that the oldest, outermost shell seen in the Webb image may have been launched about 150 years before the latest shell, which is still in its infancy and from the bright pair of stars driving the physics at the center of the system. getting away.
With its spectacular plumes and wild fireworks, Wolf-Rayets has delivered one of the most intriguing and intricately patterned images ever released by the new Webb telescope.
It was one of the first images Webb took. Astronomers are on the edge of our seats, waiting to see what new wonders this observatory will give us.