Astronomers have offered an explanation for the shapes of planetary nebulae. The discovery is based on a set of observations of stellar winds around aging stars. Contrary to consensus, the team found that stellar winds are not spherical, but are the same size as the planet nebula. The team concludes that interactions with stars or exoplanets coming together shape both stellar winds and planetary nebulae. The findings were published in Science.
The dying stars swell and eventually become red giants. They produce stellar winds, the flow of particles that expel the star, causing them to lose mass. Because detailed observations were lacking, astronomers have always believed that these winds were spherical, like the stars around them. As the star moves forward, it heats up again and the stellar radiation shines, sparking extended layers of stellar material, forming the planet nebula.
Over the centuries, astronomers had come to know about the extraordinary variety of colorful shapes of planetary nebulae. The nebula all seem to have a certain symmetry but are almost never rounded. “The sun – which will eventually become a red giant – is round like a billiard ball, so we were surprised: how could a star produce all these different shapes?” The same author says KU Leuven.
His team observed stellar winds among cool red giant stars with the world’s largest radio telescope with the ALMA Observatory in Chile. For the first time, he gathered a large, detailed collection of commentaries, each of them using the exact same method. It was important that in order to be able to directly compare the data and exclude bias.
Astronomers were surprised by what they saw. “We saw that these winds are anything but symmetrical or round,” Professor Dasein says. “Some of them are actually similar in size to the planet nebula.”
Astronomers could also identify different categories of shapes. “Some stellar winds were disc-shaped, others were spiral, and in a third group, we identified cones.” This is a clear indication that the shapes were not randomly drawn. The team realized that other, lower-mass stars or even heavier planets around the dying star were producing different patterns. These companions are too small and dim to detect directly. Desine explains, “Just as a spoon that you shake in a cup of coffee with some milk can create a spiral pattern, the partner sucks the material for it.
The team put this theory into the model, and in fact: the size of stellar winds can be explained by the peers they surround, and the rate at which the cool evolving star is losing its mass due to stellar wind is an important parameter. Decin: “All our observations can be explained by the fact that the stars have a companion.”
Until now, calculations about the evolution of stars were based on the assumption that stars like the aging sun have stellar winds that are spherical. “Our values change drastically. Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimates of older stars can be inaccurate up to a factor of 10.” The team is now conducting further research to see how this may affect the calculation of other important features of stellar and galactic evolution.
This study also helps to visualize what the sun might look like when it dies in 7000 million years. “Jupiter or even Saturn – because they have such a large mass – is going to affect whether the sun spends its last millennium at the heart of a spiral, a butterfly, or any other fascinating shapes that we planet today. See in the nebula “note note. “Now our calculations indicate that a weak spiral will form in the stellar air of the old dying sun.”
“We were very excited to explore the first picture,” says co-writer Miguel Montarges (KU Leven). “Each star, which was only a number before, became a person by itself. Now, we have their own identity. It’s the magic of having high-precision observations: stars are no longer just numbers.”
The study is part of the ATOMIUM project, which aims to learn more about the physics and chemistry of old stars. “Cool aging stars are considered boring, old and simple, but we now prove that they are not: they tell the story after everything they say. It took us a while to realize that stellar Winds may have the shape of rose petals (see, for example, the stellar wind of R Aquilae), but, as Antoine de Saint-Exupéry states in his book Le petit prince: “C’est le temps que tu as perdu pour ta rose, qui fait ta rose si important.” (“It’s the time spent on your rose that makes your rose so important.”)
The stellar air of old stars reveals the existence of a companion
L. Dickin al al., “(Sub) stellar mates shape the winds of evolved stars,” Science (2020). science.sciencemag.org/cgi/doi… 1126 / science.abb1229
Quotes: Astronomers captured stellar winds in unprecedented detail (2020, 17 September). Retrieved 18 September 2020 from https://phys.org/news/2020-09-astronomers-capture-stellar-unpreprise.html.
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