Alien megastructures? Cosmic fingerprint? What’s behind a James Webb Telescope photo that stumped even astronomers?

Credit: NASA/ESA/CSA/STScI/JPL/Caltech

In July, a puzzling new image of a distant extreme star system surrounded by surreal concentric geometric rungs had even astronomers scratching their heads. The image, which looks like a kind of “cosmic fingerprint,” comes from the James Webb Space Telescope, NASA’s newest flagship observatory.

The Internet was immediately filled with theories and speculation. Some in the wild fringe even claimed it as evidence of “alien megastructures” of unknown origin.

Fortunately, our team at the University of Sydney had already been studying this same star, known as WR140, for more than 20 years, so we were in a prime position to use physics to interpret what we were seeing.

Our model, published in Natureexplains the strange process by which the star produces the dazzling pattern of rings seen in Webb’s image (now published in nature astronomy).

The secrets of WR140

WR140 is what is called a Wolf-Rayet star. These are among the most extreme stars known. In a rare but beautiful display, they can sometimes emit a plume of dust into space that stretches hundreds of times the size of our entire Solar System.

The radiation field around Wolf-Rayets is so intense that dust and wind are swept outward at thousands of kilometers per second, or about 1% of the speed of light. While all stars have stellar winds, these achievers push something more like a stellar hurricane.

Alien megastructures?  Cosmic fingerprint?  What's behind a James Webb Telescope photo that stumped even astronomers?

The binary stars of the WR140 system. Credit: Amanda Smith/IoA/Cambridge University, Author provided

Critically, this wind contains elements such as carbon that flow 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, which is itself a massive blue supergiant with a ferocious wind of its own.

Only a few systems like WR140 are known in our entire galaxy, but these select few offer the most unexpected and beautiful gift to astronomers. The dust does not simply flow off the star to form a nebulous ball as might be expected; instead, 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 soot plume then naturally coils into a spiral, much like the stream from a rotating garden sprinkler.

WR140, however, has a few more tricks up its sleeve that add a richer complexity to its eye-catching display. The two stars are not in circular but elliptical orbits, and in addition, dust production turns on and off episodically as the binary approaches and recedes from the point of closest approach.

Every time WR140 and its binary companion star are close enough, a pulse of dust streams out into space.

An almost perfect model

By modeling all of these effects in the three-dimensional geometry of the dust plume, our team tracked the location of the dust features in three-dimensional space.

By carefully labeling images of the expanding flow taken at the Keck Observatory in Hawaii, one of the world’s largest optical telescopes, we found that our model of the expanding flow fit the data almost perfectly.

Except for one small inconvenience. Close to the star, the dust was not where it was supposed to be. Chasing down that little misfit turned out to lead us right into a phenomenon never before caught on camera.

the power of light

We know that light carries momentum, meaning that it can exert a push on matter known as radiation pressure. The result of this phenomenon, in the form of matter floating at high speed around the cosmos, is evident everywhere.

But it has been a remarkably difficult process to catch in the act. The force vanishes rapidly with distance, so to see the acceleration of the material it is necessary to follow the motion of matter very precisely in a strong radiation field.

In every eight-year orbit, a new ring of dust forms around WR140. Credit: Yinuo Han/Cambridge University, provided by the author

This acceleration turned out to be the only element missing from the models for the WR140. Our data didn’t fit because the rate of expansion wasn’t constant: the dust was getting a boost from radiation pressure.

Capturing that for the first time on camera was something new. In each orbit, it is as if the star unfurls a giant sail made of dust. As it catches the intense radiation emanating from the star, like a yacht taking a blast, the dusty sail makes a sudden leap forward.

smoke rings in space

The end result of all this physics is stunningly beautiful. Like a mechanical toy, WR140 inflates precisely sculpted smoke rings with every eight-year orbit.

Each ring is engraved with all this wonderful physics written in the detail of its shape. All we have to do is wait and the expanding wind inflates the dust layer like a balloon until it’s big enough for our telescopes to take pictures of.

Then, eight years later, the binary returns to its orbit and another shell identical to the previous one appears, growing inside the bubble of its predecessor. The shells keep piling up like a ghostly game of giant nesting dolls.

Alien megastructures?  Cosmic fingerprint?  What's behind a James Webb Telescope photo that stumped even astronomers?

The James Webb Space Telescope image (left) confirmed the model’s predictions (right) in detail. Credit: Yinhuo Han/Peter Tuthill/Ryan Lau, provided by the author

However, the true extent to which we had hit on the correct geometry to explain this intriguing star system did not become apparent to us until the new Webb image arrived in June.

Here were not one or two, but more than 17 exquisitely sculpted shells, each a near-exact replica nested within the last. That means the older, outer shell visible in Webb’s image must have been launched about 150 years earlier than the newer shell, which is still in its infancy and speeding away from the luminous pair of stars that drive the physics at heart. of the system.

With their spectacular plumes and wild fireworks, the Wolf-Rayets have provided one of the most intriguing and intricately patterned images ever released by the new Webb telescope.

This was one of the first images taken by Webb. Astronomers are all on the edge of our seats, waiting for what new wonders this observatory will convey to us.

Dust plumes seen being ‘pushed’ into interstellar space by intense starlight

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