Alien megastructures? Cosmic thumbprint? What’s behind a James Webb telescope photo that had even astronomers stumped?

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

In July, even astronomers were left scratching their heads at a puzzling new image of a distant extreme star system surrounded by surreal concentric geometric rungs. The photo, which looks like a sort of “cosmic thumbprint,” came from the James Webb Space Telescope, NASA’s newest flagship observatory.

The internet immediately perked up with theories and speculation. Some on the wild fringe even claimed it as evidence for “alien megastructures” of unknown origin.

Fortunately, our team at the University of Sydney had studied this star, known as WR140, for over 20 years, so we were in a great position to use physics to interpret what we saw.

our model, published in Natureexplains the strange process by which the star produces the dazzling pattern of rings seen in the Webb image (now itself published in Natural Astronomy).

The secrets of WR140

WR140 is what a . is called Wolf-Rayet star. These are among the most extreme stars known. In a rare but beautiful display, they can sometimes send a dust plume into space 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 out at thousands of miles per second, or about 1% the speed of light. While all stars have stellar winds, these overachievers are driving something more akin to a stellar hurricane.

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

Crucially, this wind contains elements such as carbon that flow out to form dust.

WR140 is one of the few dusty Wolf-Rayet stars in a binary system. It orbits another star, which is itself a huge blue supergiant with its own raging wind.

There are only a handful of systems like WR140 known in our entire galaxy, but this select group provides astronomers with the most unexpected and beautiful gift. Dust doesn’t just flow out of the star to form a hazy ball, as you might expect; instead, it only forms in a cone-shaped region where the two stars’ winds collide.

Because the binary star is in constant orbital motion, this shock front must also rotate. The soot plume is then naturally coiled into a spiral, in the same way as the jet of a rotating garden sprinkler.

However, WR140 has a few more tricks up its sleeve and brings more rich complexity to its garish display. The two stars are not in circular but elliptical orbits, and dust production occasionally switches on and off as the binary star approaches and exits its closest approach.

Whenever WR140 and its binary star are close enough, a pulse of dust flows 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 dust features in three-dimensional space.

By carefully tagging photos 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 matched the data almost perfectly.

Except for one minus. Near the star, the dust was not where it should be. Chasing that little misfit turned out to lead us straight to a phenomenon never before captured on camera.

The power of light

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

But it was a remarkably difficult process to catch in the act. The force decreases rapidly with distance, so to see how material is accelerated, you have to very closely monitor the movement of matter in a strong radiation field.

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

This gear turned out to be the only missing element in the WR140 models. Our data was incorrect because the expansion rate was not constant: the dust was boosted by radiation pressure.

Capturing that on camera for the first time was something new. In each orbit, it is as if the star is unfolding a gigantic sail of dust. When it catches the star’s intense radiation, like a yacht catching a gust of wind, the dusty sail makes a sudden leap forward.

Smoke circles in space

The final result of all this physics is breathtakingly beautiful. Like a toy clockwork, the WR140 blows precision-shaped smoke rings with every eight-year track.

Each ring is engraved with all this beautiful physics written into the detail of its shape. All we have to do is wait and the expanding wind inflates the dust envelope like a balloon until it is big enough for our telescopes to take images.

Then, eight years later, the binary returns to its orbit and another shell appears identical to the previous one, growing into its predecessor’s bubble. Shells continue to pile up like a ghostly array of giant nesting dolls.

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

However, the true extent to which we had found the correct geometry to explain this intriguing galaxy only became clear to us when the new Webb image arrived in June.

Here were not one or two, but more than 17 beautifully carved shells, each an almost exact replica nestled within the previous. That means the oldest, outermost shell visible in the Webb image must have been launched about 150 years before the newest shell, which is still in its infancy and moving faster and faster from the luminous pair of stars that power physics at the heart of powers the system.

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

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


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


Provided by The Conversation

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