A pair of stars in our galaxy reveals how light pushes matter. It’s the first time anyone has seen directly how the pressure of starlight changes the flow of dust in space.
Such radiation pressure influences how dust is removed from regions near young stars and guides the formation of gas clouds around dying stars (Serial number: 09/22/20). The dust pattern surrounding a stellar pair 5,600 light-years away in the constellation Cygnus provides a rare laboratory to observe the effect in actionastronomer Yinuo Han and colleagues report in the Oct. 13 Nature.
Astronomers have long known that the dust that emerges from the star WR 140 and its companion is made up of gas from these two stars colliding and condensing into soot. But images of the pair taken over the course of 16 years show that the dust speeds up as it moves away from the stars.
The dust initially leaves the stars at about 6.5 million kilometers per hour, the researchers report. That’s fast enough to make a trip from Earth to the Moon in just over half a day. Over the course of a year, the dust accelerates to almost 10 million km/h.
The revelation came from comparing the positions of concentric dust layers year after year and deducing a velocity. The researchers’ calculations show that the force accelerating the dust is the pressure exerted by light radiated from the stars, says Han, of the University of Cambridge. “radiation pressure [becomes apparent] only when we put all the images side by side.”
Those dust layers not only feel the push of light, but also extend further than any telescope could see, until this year. Images from the James Webb Space Telescope, or JWST, represent more of the dust layers around WR 140 and its companion than ever before, Han and another team report Oct. 12 at nature astronomy.
At first glance, the intricate patterns that surround the stars resemble a giant spider’s web. But the researchers’ analysis reveals that they are actually huge, expanding cone-shaped layers of dust. They are nested within each other, with a new one forming every eight years as the stars complete another trip around their orbits. In the new images, the shells look like sections of rings because we’re looking at them from the side, Han says.
The patterns do not completely surround the stars because the distance between the stars changes as they orbit each other. When stars are far apart, the density of the colliding gas is too low to condense into dust, an effect the researchers expected.
What surprised them is that the gas doesn’t condense well when the stars are closer together, either. That suggests there’s a “Goldilocks zone” for dust formation: dust forms only when the separation between stars is just right, creating a series of concentric dust layers moving away from the duo.
“Their Goldilocks zone is a new idea,” says astrophysicist Andy Pollock of the University of Sheffield in England, who was not part of either study. “Something similar happens in my X-ray field.”
In his work, Pollock has observed that WR 140 and its partner emit more X-rays as the stars get closer to each other, but less as they get very close, suggesting that there is also a Goldilocks zone for stars. X-rays from stars. . “It would be interesting to see if there is any connection” between the two types of Goldilocks zones, he says. “This all has to fit together somehow.”