The atoms that make up life on Earth—carbon, oxygen, nitrogen, and more—were forged inside stars long before our planet existed.
For decades, astronomers believed they understood how these elements were spread through the galaxy. A new study, however, shows that a key part of that story needs to be rewritten.
Researchers at Chalmers University of Technology in Sweden have found that starlight and stardust alone are not powerful enough to drive the strong winds of red giant stars.
These winds are responsible for carrying life’s essential ingredients into space, where they later become part of new stars, planets, and eventually living organisms.
The findings come from detailed observations of a nearby red giant star called R Doradus and were published in the journal Astronomy & Astrophysics.
Red giant stars are aging stars that have exhausted much of their fuel. As they grow larger and cooler, they begin to lose mass through slow but powerful stellar winds.
Over time, these winds enrich the space between stars with heavy elements, playing a crucial role in shaping galaxies and enabling the formation of future planetary systems.
Until now, scientists believed these winds were driven mainly by starlight pushing on newly formed dust grains around the star.
The idea was simple: dust forms close to the star, light hits the dust, and radiation pressure pushes it outward, dragging gas along with it. This process was thought to explain how material escapes the star’s gravity.
The new observations challenge that explanation. Using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile, the team studied light scattered by dust grains surrounding R Doradus. By carefully measuring how the light was polarized at different wavelengths, the researchers were able to determine the size and makeup of the dust particles.
They found that while dust is indeed present, the grains are extremely small—about one ten-thousandth of a millimeter across. Computer simulations showed that grains of this size simply cannot be pushed strongly enough by starlight to escape the star and drive the observed winds.
In other words, the dust is there, and it glows in the star’s light, but it does not provide the necessary force. This result overturns a long-standing assumption in stellar physics.
So what does power these winds? The researchers suggest several possibilities. Red giant stars are highly dynamic objects, with massive bubbles of hot gas rising and falling on their surfaces. The stars also pulsate, expanding and contracting over time. These violent motions may help lift material away from the star, allowing dust and gas to escape together. Sudden bursts of dust formation could also play a role.
Earlier observations with the ALMA telescope have already revealed giant convective structures on R Doradus, supporting the idea that complex physical processes are at work.
While the new findings complicate the picture, they also open exciting new directions for research.
Understanding how stellar winds truly work is essential for explaining how the elements that make up life are spread across the universe—and ultimately, how planets like Earth come to exist at all.
Source: Chalmers University of Technology.
