Where does the awesome “spider web” in the latest JWST image come from?

Spoiler: Arachnitects have nothing to do with it.

Since NASA unveiled its first contributions on July 12, the James Webb Space Telescope has not stopped capturing fantastic images of the cosmos. Recently, he added an astronomical curiosity to his hunting list with a new object as magnificent as it is intriguing.

In the middle of this composite image, we distinguish a binary star system called WR 140, but it is not the most striking element. Rather, it is the concentric lines and rings emerging from it that immediately catch the eye.

Together, they form a structure that almost looks like a huge cosmic spider’s web; a rather extraordinary image which may remind fans of the cartoon of the work of the Arachnitects FinalSpace. But if WR 140 is of such interest to astronomers, it is not for aesthetic reasons; it is above all because it is a manifestation of a phenomenon that seems quite rare on the scale of the universe.

The straight lines that emerge from the point of light are not very interesting. They are simply what are called diffraction aigrettes (diffraction spikes in English). As their name suggests, these are image imperfections related to the diffraction of light. In the case of the Webb, they are caused by the imperfections of the main mirror and by the structure which supports the secondary mirrors; we find them on all the photos of the telescope.

A neighborhood quarrel with serious consequences

These luminous lines are therefore not “real” and do not correspond to a phenomenon which takes place in the vicinity of the star; it is simply a visual artifact. On the other hand, this is not the case for concentric rings; they result from a very real phenomenon, rare, difficult to observe, and by extension very interesting for specialists. And to understand their origin, it is necessary to take an interest in the particularities of the stars that make up the system.

© NASA, ESA, CSA, Leah Hustak (STScI), Joseph DePasquale (STScI)

On one side is WR 141, a Type O star. These are the most massive stars that exist; they are also extremely hot and shiny. They burn their reserves at a maddening rate, which gives them a very limited life expectancy. These Type O stars also emit powerful stellar winds.

On the other, we have WR 140, a representative of a rare category that astronomers consider to be descendants of the Type O stars above; we speak of a Wolf-Rayet star. These are extremely hot, massive and luminous bodies that are approaching the end of their life cycle; they emit what can be assimilated to a long death rattle by expelling large quantities of matter in the form of extremely fast stellar winds before ending their life in apotheosis thanks to a gigantic supernova.

These two objects are part of the same binary system, that is to say two gravitationally linked stars which orbit around a common barycenter. Sometimes the orbits of the two stars can be nearly circular and concentric; in this case, they therefore describe nice circles and can revolve around each other for millennia without crossing each other once.

A cosmic “onion” illuminated by the stars

But in the case of WR 140, the situation is quite different since the two orbits are elliptical and of very different sizes. The two stars therefore periodically pass very close to each other; this generates a violent collision between the stellar winds from the two stars, as shown by this model.

With each pass, the associated shock wave tears off a large quantity of material which forms a dusty “bubble” around the point of impact. Over time, this phenomenon produced an “onion” structure, with many concentric bubbles. According to ScienceAlert, which identified this work, it is carbonaceous material, and therefore likely toabsorb ultraviolet radiation from the two stars. This dust therefore begins to heat up and radiate in the infraredwhich allows the JWST to observe them.

These circles spotted by the JWST are therefore not rings, but dust bubbles highlighted by starlight. And the other very interesting point is that the system has a very precise periodicity; the two stars “cross” and therefore produce a bubble every 7.94 years.

This means that if we could observe all of these bubbles, we would also be able to determine precisely since when the two stars have been interacting in this way, exactly as one would determine the age of a tree by counting the rings!

The concrete implications of this discovery are still quite unclear as it stands, as the astronomers behind this observation are still preparing the research paper on the matter. We will therefore have to wait for the end of the peer review process to know precisely the ins and outs of this discovery. But what is certain is that the Webb has not finished giving food for thought to specialists and delighting its audience!

The pre-publication research paper is available here.

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