Two stars in our galaxy are revealing the effects of light on matter. It’s the first time anyone has directly seen how the pressure of light from stars changes the flow of dust in space.
This radiation pressure affects how dust is cleared from regions near young stars, and helps to guide the formation of Gas clouds around dying stars (SN: 9/22/20). The dust pattern surrounding the Cygnus constellation’s stellar pair is providing this information Rare laboratory for observing the effect in actionYinuo Han (astronomer) and colleagues report in the Oct. Nature.
Astronomers knew for a long time that the dust that emerges from the star WR140 is made from gas from the stars colliding, condensing into soot. However, 16-year-old images of the pair show that the speed of the dust’s escape from the stars is evident.
Researchers report that dust initially leaves the stars at a speed of 6.5 million kilometers an hour. That’s fast enough to make a trip from Earth to the moon in a little over half a day. The dust travels at speeds of nearly 10,000,000 km/h over the course of a single year.
This was possible by comparing the concentric dust shell positions year to year and calculating a speed. 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 next to each other.”
Not only are those layers of dust feeling light’s push, they also extend out farther than any telescope could see — until this year. Images from the James Webb Space Telescope or JWST You can see more dusty layers around WR 140 or its companionHan and another member of the team report on October 12, 2012, in a way unlike any other. Astronomy in Nature.
The intricate patterns around the stars look like a huge spiderweb at first glance. But the researchers’ analysis reveals that they are actually enormous, expanding, cone-shaped dust shells. They’re nested inside each other, with a new one forming every eight years as the stars complete another journey around their orbits. Han says that the new images show the shells looking like pieces of rings, because they are viewed from the side.
The patterns don’t completely surround the stars because the distance between the stars changes as they orbit one another. When the stars are far apart, the density of the colliding gas is too low to condense to dust — an effect the researchers expected.
What surprised them is that the gas doesn’t condense well when the stars are closest together either. That suggests there’s a “Goldilocks zone” for dust formation: Dust forms only when the separation between the stars is just right, creating a series of concentric dust shells rippling 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. “A similar sort of thing happens in my field of X-rays.”
In his work, Pollock has observed that WR 140 and its partner emit more X-rays as the stars approach each other, but then fewer as they get very close together, suggesting there’s a Goldilocks zone for X-rays coming from the stars as well. “It would be interesting to see if there’s any connection” between the two types of Goldilocks zones, he says. “All of this must somehow fit together.”
