It is a binary star known as Wolf-Rayet 140 located more than 5,000 light-years away from Earth in the Cygnus constellation. And this spectacular image from the depths of the cosmos does not show evidence of an alien megastructure, as has been talked about on some social networks, but the result of a rare type of star and its companion locked in a celestial dance. In short, we can say that it is essentially cosmic dust.
There are at least 17 rings
Captured by the NASA/ESA/CSA James Webb Space Telescope in July 2022, it has baffled astronomers around the world, even sparking this unusual speculation that it could be evidence of an extraterrestrial megastructure. But thanks to two new studies, astronomers explain that the 17 concentric rings around WR 140 are actually a series of dust layers created by the interaction between a pair of hot stars.
But Webb aside, this binary star has been monitored for two decades with one of the world’s largest optical telescopes at the Keck Observatory in Hawaii.
Also known as HD 193793, HIC 100287, or IRAS 20187+4341, the system is composed of an enormous Wolf-Rayet star and an even larger blue supergiant star, gravitationally bound in a 7.93-year orbit. It turns out that WR 140 spews out dust plumes every eight years that stretch thousands of times the distance between Earth and the Sun. And while all stars generate stellar winds, those from Wolf-Rayet stars may be more like a stellar hurricane. .
“Like clockwork, WR 140 inflates a sculpted smoke ring every eight years, which then inflates in the stellar wind like a balloon,” said Professor Peter Tuthill, an astronomer at the Sydney Institute for Astronomy at the University of Sydney. “Eight years later, when the binary returns to its orbit, another ring appears, just like the previous one, going out into space inside the bubble of the previous one.”
The importance of cosmic dust
Because the two stars are in elliptical rather than circular orbits, dust production turns on and off as WR140’s binary companion approaches and then recedes from the point of closest approach. Light is known to carry momentum, exerting a push on matter known as radiation pressure. Direct recording of acceleration due to forces other than gravity is rarely observed, and never in a stellar environment like this one.
“It’s hard to see starlight causing an acceleration because the force fades with distance and other forces quickly take over,” said Yinuo Han, an astronomer at the University of Cambridge’s Institute for Astronomy. “To witness the acceleration to the level where it becomes measurable, the material must be reasonably close to the star or the source of the radiation pressure must be stronger.”
Thus, the orbit of the stars joins them once every eight years and, like the rings of a tree trunk, the loops of dust mark the passage of time.
“WR 140 is a binary star whose fierce radiation field supercharges these effects , putting them within reach of our high-precision data,” the experts clarify.
analyzing the dust
Astronomers think that WR 140’s winds also cleared the surrounding area of debris that it might otherwise collide with, which could explain why the rings are so pristine.
The UK Astronomy Technology Center (UK ATC) played a key role in the design and construction of MIRI’s spectrometer, one of James Webb’s instruments, which was used to reveal the composition of dust, made up mainly of the material ejected by the star. Experts believe that the Wolf-Rayet star in this particular pair may have lost more than half of its original mass through this process of powerful winds pushing huge amounts of gas into space. Hydrogen, the most common element found in stars, cannot form dust on its own.
Thanks to the Webb, researchers will be able to learn much more about WR140 and similar systems.
“The Webb telescope offers new extremes of stability and sensitivity,” said Dr. Ryan Lau, an assistant astronomer at the US National Optical and Infrared Astronomy Research Laboratory and lead author of the JWST study published in Nature Astronomy . “Now we will be able to make observations like this much more easily than from the ground, opening a new window into the world of Wolf-Rayet physics.”
Dust is one of the most important components of the universe, as it plays a crucial role in the evolution of galaxies and is an essential ingredient for the formation of stars and planets.
Referencia: Y. Han et al. 2022. Radiation-driven acceleration in the expanding WR 140 dust shell. Nature 610, 269-272; doi: 10.1038/s41586-022-05155-5
R.M. Lau et al. Nested dust shells around the Wolf-Rayet binary WR 140 observed with JWST. Nat Astron, published online October 12, 2022; doi: 10.1038/s41550-022-01812-x
