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Astronomers observe stellar winds from aging stars in unprecedented detail

Sept. 17 (UPI) — Astronomers have captured high resolution images of stellar winds emanating from a diversity of aging stars.

The observations, detailed Thursday in the journal Science, suggest the dramatic shapes of planetary nebulae are formed by interactions between stellar winds and nearby planets and stars.


As dying stars swell and cool, they expel particles and shed mass, producing stellar winds. As the red giants continue to age and evolve, they heat up again, casting off layers of ejected stellar material. Stellar radiation causes these sloughed layers to glow, creating what astronomers call planetary nebulae.

Scientists have long struggled to explain the wide variety of shapes and colors that characterize planetary nebulae.

“The sun, which will ultimately become a red giant, is as round as a billiard ball, so we wondered: how can such a star produce all these different shapes?” study co-author Leen Decin, astronomer at the Catholic University of Leuven in Belgium, said in a news release.

Decin and her colleagues used the ALMA Observatory in Chile to precisely observe dozens of red giants. Scientists were careful to use the exact same observational techniques when surveying each new stellar target, collecting a standardized database of stellar wind observations.

“We noticed these winds are anything but symmetrical or round,” Decin said. “Some of them are actually quite similar in shape to planetary nebulae.”

But while researchers observed a variety of shapes, they weren’t entirely idiosyncratic. Astronomers were able to group the stellar winds into categories.

“Some stellar winds were disk-shaped, others contained spirals, and in a third group, we identified cones,” Decin said.

Researchers realized the different shapes were caused by interactions between stellar winds and low-mass companion stars or heavy, nearby planets.

“Just like how a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind,” Decin said.

When scientists simulated interactions between stellar winds and nearby stars and planets, their computer models produced results identical to their ALMA observations.

Until now, most models of stellar evolution have been based on the assumption that stellar winds are spherical.

“Our findings change a lot,” said Decin. “Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimate of old stars could be wrong by up to a factor of ten.”

Scientists used their findings to model what the sun’s stellar winds will look like when it dies in 7,000 million years. Their simulations showed the influence of Saturn and Jupiter will cause the sun’s stellar winds and planetary nebulae to take on a weak spiral shape.

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