The James Webb Space Telescope has captured an image of bright light from a star pushing multiple clouds of dust into space.
The propulsive effect of the star is what is known as radiation pressure. Radiation pressure prevents stars from collapsing under their own gravity and creates the bright, smudgy tails of comets as they pass close to the sun. But the new image is the most complete picture yet of the phenomenon taking place around a star.
The strange image, that was first released in July by citizen scientist Judy Schmidt, shows a pair of stars in WR140, located 5,600 light-years away in the constellation Cygnus. The binary star system is surrounded by an onion-like shell with nearly 20 concentric ripples. Once released, the image sparked a lot of online speculation about what could be causing the effect, now another team of researchers has finally provided the answers in a paper published on October 12 in the journal Nature (opens in new tab).
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The ripples are large plumes of glowing dust and soot that are thrown up as a pair of streaming stars in WR140 hover close by each other in an elliptical orbit that they complete about every eight years.
As they both approach, the 1,864 miles per second (3,000 kilometers per second) solar winds collide with each other, forming a mass of material in space that slowly expands to form rings. As the plumes are only ejected when the stars are close together, the distance of the rings is determined by their orbital period. This means that the dust builds up at regular intervals, and the rings of the cloud can be counted like tree rings to find the age of the outermost ripple — with 20 visible rings corresponding to 160 years of dust.
But these ripples do not expand outward at a constant speed. Instead, they accelerate, pushed by periodic throws photons, or light particles, from nearby stars. It is this acceleration that changes the gap distance between the rings.
“In a sense, we always knew that this must be the reason for the outflow, but I never dreamed that we could see the physics working like this,” study co-author Peter Tuthill, an astrophysicist at the University of Sydney in Australia, said in a statement. “When I look at the data now, I see the plume of WR140 unfurling like a giant sail made of dust. When it catches the photon wind rushing from the star, like a yacht catching a gust, it takes a sudden leap forward.”
One of the duo’s stars is a Wolf-Rayet star, a rare type of slowly dying star that has lost its outer shell of hydrogen, leaving it to eject ionized helium, carbon and nitrogen from its interior. These stars will explode as supernovas one day, but until then the radiation pressure produced by the light unfurls their contents in an explosion, stretching them like giant ghost jellyfish across the night sky. The superheated elements ejected, especially the carbon that turns to soot, remain hot enough to glow brightly in the infrared spectrum.
The other member of the pair is an O-type blue supergiant, one of the most massive classes of stars. Hot, bright and massive, the supergiant is also leaking gas and destined to go supernova. When the two stars fly close together, their solar winds combine into a huge cone of material that is ejected into space.
“Like clockwork, this star spews out sculptural smoke rings every eight years, with all this wonderful physics written down and then billowed in the wind like a banner for us to read,” Tuthill said. “Eight years later, as the binary returns to its orbit, another appears just like the first, blasting off into space inside the first’s bubble, like a set of giant nesting Russian dolls.”
The highly predictable timing of the puffs and their long-distance extension gave astronomers a unique opportunity to study the underlying physics of the outbursts.
For detail his shiny rings infrared soot, astronomers turned for the first time to one of the world’s largest optical telescopes – the Keck Observatory in Hawaii and its 10-meter mirror. By training the telescope’s infrared camera on the distant rings, the researchers watched them push outward and grow slowly over the course of 16 years. Then, continuing their work, the scientists worked with a second team to take another picture with it James Webb Space Telescope which showed all twenty rings in crystal clear clarity.
After trying and failing to model what they had seen, astronomers were initially confused.
“In the absence of external forces, each dust spiral should expand at a constant speed,” first author Yinuo Han, an astronomer at the Institute of Astronomy in Cambridge, England, said in the statement. “We were confused at first because we couldn’t get our model to match the observations, until we finally realized we were seeing something new. The data did not match because the rate of expansion was not constant, but rather accelerating. We caught it for the first time on camera.”
The rings of dust were accelerated by periodic nudges from starlight, which, like all light, carries momentum. According to the researchers, astronomers have often indirectly seen the fingerprints of this phenomenon in the inexplicably high speeds of some matter in the universe, but the radiation pressure of starlight has never been directly measured until now. This is because near the stars, where the radiation pressure is strongest, the thrusts it produces are often masked by extremely strong gravitational fields.
Researchers say that with the James Webb Space Telescope now fully operational, they will be able to take an even deeper look at WR140 and other strange systems where new physics may be lurking.
“The Webb telescope offers new extremes in stability and sensitivity,” Ryan Lau, an infrared astronomer at the National Science Foundation who led the James Webb division of the research, said in the statement. “We will now 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.”