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For years, astronomers have known that Sun-like stars lose most of their mass as they transition to the red giant stage, but this occurrence remained unexplainable. That is, until an international team of astronomers believes that they have solved the mystery. This discovery can shed light on stellar evolution and, more specifically, how stars age.
When stars like our Sun turn into red giants, they shed off their outer shells of gas and expand and become hundreds of times larger. Stars have “atmospheres,” which consist of powerful winds of gas and dust (which makes up much of a stars’ mass) that the stars emanate, and during their transition, the winds become 100 million times more violent. These “superwinds” occur for 10,000 years – the length of time during which usually red giants live – and cause stars to lose more than half their mass or as much so that only their cores remain.
What causes the “superwinds” has remained elusive for astronomers. Before, it had been thought that the amount of light from the red giants (which are considerably bright for main sequence stars) was absorbed by the dust grains, which were then pushed out by the light. However, all the models that were produced did not coincide with this theory.
The team consists of astronomers from the University of Manchester, Oxford and Macquarie University, University of Sydney, Australia, Paris-Diderot University, and New South Wales. Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in northern Chile, the team looked at dying stars with a powerful resolution that allowed them to see the stars’ winds. They were surprised to see how many dust grains whirled around and how large they were. However, they were no bigger than grains of sand, but they were large for their size.
Using this information, the team was able to discover that these dust grains acted as mirrors, reflecting light from other stars. Since the grains remain cold, the star is able to push them out at 10 kilometers per second (20 million miles per hour).
“The dust and sand in the superwind will survive the star and later become part of the clouds in space from which new stars form,” Professor Albert Zijlstra, from the University of Manchester’s Jodrell Bank Observatory, said in the University of Manchester’s news release.
“The sand grains at that time become the building blocks of planets,” he continued. “Our own Earth has formed from star dust. We are now a big step further in understanding this cycle of life and death.”
Now that the mystery of superwinds has been solved, there is another for astronomers to figure out: how these dust grains form and are able to exist at their large size so close to the stars.