Light from stars and the dust it illuminates may not be enough to drive the powerful winds that carry life’s essential elements across the galaxy. That is the conclusion of a new study from Chalmers University of Technology in Sweden, based on close observations of the red giant star R Doradus. The findings challenge a long-standing explanation for how atoms crucial to life are spread through space.
“We thought we had a good idea of how the process worked. It turns out we were wrong. For us as scientists, that’s the most exciting result,” says Theo Khouri, an astronomer at Chalmers and a joint leader of the research.
Why Stellar Winds Matter for Life
Understanding how life began on Earth requires knowing how stars distribute the elements that make planets and biology possible. For many years, astronomers have believed that stellar winds from red giant stars are powered when starlight pushes against newly formed dust grains. These winds are thought to spread carbon, oxygen, nitrogen, and other life essential elements throughout the galaxy. New observations of R Doradus suggest this explanation does not fully work.
Red giant stars are aging, cooler stars related to our Sun. As they approach the final stages of their lives, they shed large amounts of material through strong stellar winds. This process enriches the space between stars with the raw materials needed to form future stars, planets, and eventually life. Even so, the exact force behind these winds has remained uncertain.
Dust Grains Too Small to Escape
By studying R Doradus, which is relatively close to Earth, astronomers discovered that the surrounding dust grains are extremely small. The grains are not large enough for starlight to push them outward with sufficient force to escape into interstellar space.
The research team, based at Chalmers University of Technology, published their results in the journal Astronomy & Astrophysics.
“Using the world’s best telescopes, we can now make detailed observations of the closest giant stars. R Doradus is a favourite target of ours — it’s bright, nearby, and typical of the most common type of red giant,” says Theo Khouri.
High Resolution Observations and Simulations
The team observed R Doradus using the Sphere instrument on ESO’s Very Large Telescope. They measured light reflected by dust grains within a region about the size of our Solar System. By studying polarized light at different wavelengths, the researchers were able to determine the grains’ size and composition. The dust matched familiar types of stardust, including silicates and alumina.
These detailed observations were combined with advanced computer simulations designed to model how starlight interacts with dust particles.
“For the first time, we were able to carry out stringent tests of whether these dust grains can feel a strong enough push from the star’s light,” says Thiébaut Schirmer.
The results were unexpected. The dust grains around R Doradus are typically only about one ten-thousandth of a millimetre across. That size is far too small for starlight alone to push the material outward and drive the star’s wind into space.
“Dust is definitely present, and it is illuminated by the star,” says Thiébaut Schirmer. “But it simply doesn’t provide enough force to explain what we see.”
Alternative Forces at Work
Because dust driven by starlight cannot fully explain the winds of R Doradus, the researchers believe other processes must play a major role. Earlier observations using the ALMA telescope revealed massive bubbles rising and falling across the star’s surface.
“Even though the simplest explanation doesn’t work, there are exciting alternatives to explore,” says Wouter Vlemmings, a professor at Chalmers and a co-author of the study. “Giant convective bubbles, stellar pulsations, or dramatic episodes of dust formation could all help explain how these winds are launched.”
More About the Research
The study, “An empirical view of the extended atmosphere and inner envelope of the asymptotic giant branch star R Doradus II. Constraining the dust properties with radiative transfer modelling,” is published in Astronomy & Astrophysics.
The work is part of the cross-disciplinary project “The origin and fate of dust in our Universe,” funded by the Knut and Alice Wallenberg Foundation. The project is a collaboration between Chalmers University of Technology and the University of Gothenburg.
The research team includes Thiébaut Schirmer, Theo Khouri, Wouter Vlemmings, Gunnar Nyman, Matthias Maercker, Ramlal Unnikrishnan, Behzad Bojnordi Arbab, Kirsten K. Knudsen, and Susanne Aalto. All co-authors are based at Chalmers University of Technology in Sweden, except Gunnar Nyman, who is at the University of Gothenburg.
The team used the Sphere (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument on the Very Large Telescope (VLT) at the Paranal Observatory in Chile. The VLT is operated by ESO, the European Southern Observatory. Sweden is one of ESO’s 16 member states.
More About the Star R Doradus
R Doradus is a red giant star located about 180 light years from Earth in the southern constellation Dorado, also known as the Swordfish. It began its life with a mass similar to the Sun but is now nearing the end of its stellar evolution. The star is classified as an AGB star (AGB = asymptotic giant branch).
Stars at this stage lose their outer layers through dense winds made of gas and dust. R Doradus sheds roughly a third of Earth’s mass every decade, while some similar stars lose mass at rates hundreds or even thousands of times higher. Several billion years from now, the Sun is expected to enter a similar phase and resemble R Doradus.
https://www.sciencedaily.com/releases/2026/01/260112001037.htm
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