Observations of the red giant star R Doradus reveal that starlight alone cannot drive its powerful stellar winds, contradicting a longstanding astronomical model. Researchers at Chalmers University of Technology in Sweden used advanced telescopes to show that surrounding dust grains are too small to be propelled by light pressure. This discovery prompts new ideas about how essential elements for life are distributed across the galaxy.
Red giant stars like R Doradus play a crucial role in enriching interstellar space with elements such as carbon, oxygen, and nitrogen, which are vital for forming planets and supporting life. For decades, scientists assumed these stars' winds were powered by starlight pushing against newly formed dust grains. However, a recent study challenges this view based on detailed observations of R Doradus, located 180 light years away in the Dorado constellation.
The research team, led by astronomers at Chalmers University of Technology, employed the Sphere instrument on the European Southern Observatory's Very Large Telescope at Paranal Observatory in Chile. By analyzing polarized light at various wavelengths, they determined that the dust grains around R Doradus measure about one ten-thousandth of a millimeter across. Computer simulations confirmed these grains are too tiny for light to exert enough force to drive the winds outward into 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," said Theo Khouri, a joint leader of the study.
R Doradus, an asymptotic giant branch star similar to what the Sun will become billions of years from now, sheds material equivalent to a third of Earth's mass every decade. Earlier ALMA telescope data showed massive bubbles on its surface, suggesting alternatives like convective motions, stellar pulsations, or sudden dust formation episodes might launch the winds.
"Even though the simplest explanation doesn't work, there are exciting alternatives to explore," noted Wouter Vlemmings, a co-author and professor at Chalmers.
The findings, published in the journal Astronomy & Astrophysics, highlight the need for further research into these dynamic processes. The study is part of a broader project funded by the Knut and Alice Wallenberg Foundation, involving collaboration with the University of Gothenburg.