In July, astronomers squibbened their heads with a disturbing new image of an extreme star system surrounded by surreal concentric geometric rungs. The image, which resembles a cosmic thumbprint, was released from the James Webb Space Telescope, the latest NASA flagship observatory.
The internet was immediately filled with theories and speculation. Some on the wild side even claimed it as evidence for alien megastructures of unknown origin.
Fortunately, our university of Sydney staff had already studied this very important scientist for over 20 years, so we were in excellent position to use physics to interpret what we were seeing.
Our model, published in Nature, explains the strange process by which the star produces the dazzling pattern of rings seen in the Webb image (itself now published in Nature Astronomy).
WR140''s secrets
WR140 is a Wolf-Rayet star known as one of the most powerful stars on the planet. They can often emit a plummet of dust into space, stretching hundreds of times the size of our entire Solar System.
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The radiation field around Wolf-Rayets is so hot, and dust and wind are swept outwards at thousands of kilometers per second, or about 1 percent the speed of light. While all stars have stellar winds, these overachievers drive something more like a gigantic hurricane.
This wind, particularly because of its lack of carbon, is capable of forming dust.
WR140 is one of the few dusty Wolf-Rayet stars discovered in a binary system. It is in orbit with another star, which is itself a massive blue supergiant with a ferocious wind of its own.
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In our entire galaxy, only a handful of systems like WR140 are known, yet these select few deliver the most unexpected and beautiful gift to astronomers. Dust does not simply flow out from the star to form a hazy ball as might be expected; rather it forms only in a cone-shaped area where the winds from the two stars collide.
Because the binary star is in constant orbital motion, this shock front must also rotate. The sooty plume then naturally gets wrapped into a spiral, in the same way as the jet from a rotating garden sprinkler.
WR140, however, has a few extra tricks up its sleeve, putting a lot of emphasis on the showy performance. The two stars aren''t on circular but elliptical orbits, and dust production turns on and off episodically as the binary approaches and departs the point of closest approach.
A model that is almost perfect
Our team analyzed the location of dust features in three-dimensional space by combining all of these influences into the three-dimensional geometry of the dust plume.
By carefully cataloging images of the expanding flow at the Keck Observatory in Hawaii, one of the world''s largest optical telescopes, we found our model of the expanding flow almost perfectly.
Except for one niggle. Close in right near the star, dust was not where it was supposed to be. Chasing that minor misfit turned out to lead us right to a phenomenon never before seen on camera.
The power of light
Light has a positive effect, which means it can exert a force on the surface of the matter, known as radiation pressure. This phenomenon, characterized by matter coasting at a high speed around the cosmos, has been revealed throughout the world.
In a strong radiation field, the force fades quickly, therefore you must look for material to be speedy.
This acceleration sounded to be the one missing element in the WR140 models. Our findings were inadequate because the expansion speed wasn''t constant: dust was getting a boost due to radiation pressure.
For the first time on camera, the star unfurls a huge sail made of dust. When it observes the huge radiation from the star, like a yacht catching a gust, the dusty sail makes a sudden leap forward.
In space, smoke ringes.
The final result of all of this physics is astoundingly stunning. WR140, like a clockwork set, puffs out precisely sculpted smoke rings every eight-year orbit.
Each ring is engraved with all of this fantastic physics written in its detail. We must wait and the expanding wind blows the dust shell like a balloon until it is large enough for our telescopes to image.
The binary returns in its orbit eight years later, and another shell appears to be identical to the one previously, which is growing inside the bubble of its predecessor. Shells keep accumulating like a ghostly set of giant nesting dolls.
The true extent to which we had pushed on the correct geometry to explain this exciting star system was jeopardized until the new Webb image was released in June.
These were not one or two, but more than 17 beautifully sculpted shells, each one a substantially exact replica nested within the one preceding it.
The oldest, outermost shell seen in the Webb image must have been built 150 years before the newest shell, which is still in its early stages, and slowly moving away from the luminous pair of stars that drive the physics at the heart of the system.
The Wolf-Rayets have created one of the most stunning and intricately patterned images ever developed by the new Webb telescope.
This was one of the first photographs taken by Webb. Astronomers are all on the edge of our seats, waiting for the new faces this observatory will display.