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Our existence, as we understand it, hinges on carbon-based chemistry, and the James Webb Space Telescope might have indicated the origins of much of that carbon. This revelation is attributed to shells of carbon dust dispersing outward from a pair of colossal stars.
The system in focus is known as WR 140, which consists of two giant stars, both fated to undergo supernova events. Situated at just under 5,000 light-years away in the constellation Cygnus (the Swan), one star is a gigantic O-type titan — the hottest and most brilliant kind, possessing a strong radiation wind. The other star is a Wolf–Rayet (WR) star, which, despite its significant mass, becomes chaotic toward the end of its lifecycle, quickly losing mass through explosive ejections, ultimately exposing its advanced core.
The stars do not orbit each other in perfect circles. Their trajectories are elongated, drawing them closer and then further apart roughly every 7.9 years. At the point of nearest approach, called periastron, the stars come within 1.3 astronomical units (AU) of each other. This distance translates to 120.8 million miles (194.5 million kilometers), slightly more than the distance from Earth to the sun.
For several months around periastron, material expelled from the Wolf–Rayet star collides with the powerful radiation wind driven by the O-type star. In the turbulence of this violent merger, particles within the stellar winds collide, compact into aggregates, and eventually cool, enabling the formation of carbon-laden dust measuring mere millionths of a meter. This dust manifests as a ring or shell encircling the two massive stars, which gradually expands outward. Eight years later, during the next periastron, a new ring emerges — and the cycle continues.
Previously, only the innermost rings from this phenomenon had been observable in visible and infrared light. Now, however, armed with its Mid-Infrared Instrument (MIRI), the JWST has captured images of 17 clumpy, concentric ring-like shells around the WR 140 system, which are expanding into space. The clumps, some comparable in size to our entire solar system, are the primary sites of dust production.
The expanding shells display impressive velocity as well. They are hurtling away from the binary system at a staggering 1,600 miles per second (around 2,600 kilometers per second). This speed is nearly 1% of the speed of light (0.87% to be exact).
“The telescope … demonstrated that the dust shells are moving outward at stable speeds, showcasing observable changes over remarkably brief periods,” remarked Emma Lieb, a doctoral researcher from the University of Denver in Colorado who spearheaded the new study, in a statement.
“We tend to perceive cosmic events as occurring at a sluggish pace, spanning millions or billions of years,” stated Jennifer Hoffman, an astronomy professor also at the University of Denver, in the same statement. “In this system, the observatory is revealing that the dust shells are expanding from year to year.”
The oldest visible shells date back 130 years, yet these close interactions between the two stars during WR 140’s Wolf–Rayet phase have been taking place for hundreds of thousands of years. The older rings would either be too faint even for the JWST to detect or have dispersed into space. It is anticipated that the system will generate tens of thousands more shells over the next few hundred thousand years as well.
And then — boom.
The Wolf–Rayet star currently possesses a mass 10 times that of our sun, and while it continues to lose mass, it will not diminish enough to evade a supernova explosion (the minimum threshold is eight solar masses). So, what occurs next with the shells of carbon-rich dust?
There are two potential outcomes. One possibility is that the supernova shockwave obliterates some or all of the dust shells; the other is that the supernova fails to ignite if the core of the star collapses under its own gravity so completely that it forms a black hole that swiftly consumes the remainder of the star. In the latter instance, there would be no supernova, and the shells of carbon dust would be permitted to expand into the vastness of space and merge with the interstellar medium that supplies the raw materials for the next generation of stars and planets.
“A fundamental inquiry in astronomy is the origin of all the dust,” posed Ryan Lau, an astronomer at the National Science Foundation’s NOIRLab in Tucson, Arizona, in the statement. “If carbon-rich dust like this survives, it could assist us in beginning to answer that question.”
Carl Sagan once poetically referred to us as “starstuff,” highlighting that we are composed of elements created in stars. If the carbon-dense dust shells captured by the JWST survive the demise of the Wolf–Rayet star, we might witness the birth of the very starstuff that contributes to the formation of life.
“We understand that carbon is vital for the development of rocky planets and solar systems similar to ours,” said Hoffman. “It’s thrilling to gain insight into how binary star systems not only generate carbon-rich dust but also propel it into our galactic vicinity.”
The latest JWST images and discoveries were presented during the 245th meeting of the American Astronomical Society on January 13th, and have been published in Astrophysical Journal Letters.
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