Dying stars grow and cool, eventually becoming red giants. They create stars
A team of scientists observed stellar winds aroundcool red giants using the ALMA observatory in Chile, the largest radio telescope in the world. For the first time, they assembled a large, detailed collection of observations, each made using the same method.
What the astronomers saw surprised them. “We noticed that these winds are not symmetrical or circular,” says Professor Decin. "Some of them are actually very similar in shape to planetary nebulae."
Professor KU Leuven discusses how herthe team uncovered an explanation for the mesmerizing shape of planetary nebulae. Their discovery is based on an unusual set of observations of stellar winds around aging stars. The team found that stellar winds have a shape similar to that of planetary nebulae and concluded that interactions with an accompanying star or exoplanet form both stellar winds and planetary nebulae. Credit: KU Leuven.
Astronomers were even able to identify different categories.forms. "Some stellar winds were disk-shaped, others spirals, and in the third group we defined cones." This is a clear sign that the shapes were not randomly generated. The team realized that other, low-mass stars or even heavy planets in the vicinity of the dying star were causing these patterns. These satellites are too small and faint to be detected directly. “Just like a spoon that you stir in a cup of coffee with milk can create a spiral pattern, a moon sucks in material to it as it orbits a star and forms a stellar wind,” explains Decin.
This gallery of images of stellar winds aroundcool aging stars exhibit a variety of morphologies, including disks, cones, and spirals. Blue represents material that is coming towards you; red — it is the material that is moving away from you. Photo: L. Decin, ESO/ALMA.
The team implemented this theory into a model, andindeed: the shape of the stellar winds can be explained by their surrounding satellites, and the rate at which a cold, evolved star loses its mass due to stellar wind is an important parameter. Decin: "All our observations can be explained by the fact that stars have a satellite."
Until now, calculations of the evolution of stars have been based onthe assumption that stellar winds are spherical in aging sun-like stars. “Our results are changing a lot. Since the complexity of stellar winds was not taken into account in the past, any previous estimate of the rate of mass loss of old stars could be erroneous up to 10 times. The team is currently conducting further research to see how this might affect calculations of other important characteristics of stellar and galactic evolution.
The study also helps to visualize howWhat the Sun might look like when it dies in 7,000 million years. “Jupiter or even Saturn—because they have so much mass—will influence whether the sun spends its last millennia at the center of a spiral, a butterfly, or whatever shape we see in planetary nebulae today,” Decin notes. “Our calculations show that a weak spiral is forming in the stellar wind of the old dying Sun."
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