In an incredible breakthrough, astronomers have managed to capture the first detailed images of turbulent activity on a star other than our own Sun. Using the powerful Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile, researchers have provided unprecedented views of the red giant star R Doradus, located about 180 light-years away in the southern constellation Dorado.
The images reveal massive gas bubbles, about 75 times the size of our Sun, rising and sinking on the surface of R Doradus. This star is nearly 350 times wider than the Sun and is in the late stages of its life, exhibiting dramatic convective processes far more significant in scale than those observed on our own solar companion.
“It is spectacular that we can now directly image the details on the surface of stars so far away,” said Behzad Bojnodi Arbab, a doctoral student at Chalmers University of Technology in Sweden and co-author of the study. The findings were recently published in the journal Nature.
R Doradus, with its enormous size and turbulent activity, serves as an ideal subject to study surface-level changes in stars. The star’s substantial size offers more surface area for activity, which facilitates detailed observation even at interstellar distances. The boiling and roiling movements on R Doradus’s surface are similar to the convective granules seen on the Sun but on an immensely larger scale.
Our Sun exhibits smaller convection granules, roughly 1,000 kilometers across, which last about 20 minutes. These granules boil up from the core and fall away at their edges. By contrast, the convective bubbles on R Doradus are much more colossal and persist for about a month, a much shorter timescale than astronomers had anticipated for such massive structures.
Wouter Vlemmings, a professor at Chalmers University and lead author of the study, expressed astonishment at the quality of data obtained. “We had never expected the data to be of such high quality that we could see so many details of the convection on the stellar surface,” Vlemmings said.
The nature of these immense convective bubbles remains somewhat mysterious. They could be the red giant equivalents of mesogranules or supergranules or might represent a different kind of granulation specific to red giant stars. Understanding these processes in detail could provide significant insights into how stars evolve, especially in their later stages.
Previous observations have shown that R Doradus spins much faster than expected for a red giant. The new study has helped clarify that this high rotational speed is not an illusion caused by the star’s boiling surface. This finding is crucial as it rules out certain hypotheses posed for other red giants like Betelgeuse.
As R Doradus undergoes the phases of its red giant stage, it presents a preview of how our Sun will behave in about five billion years. During its red giant phase, the Sun is expected to expand significantly, possibly encompassing the orbits of Mercury and Venus.
“We don’t yet know what is the reason for the difference,” Vlemmings added, noting the need for further research to understand the changes in convective behavior as stars age.
The research opens a new chapter in our understanding of stellar evolution and convective processes in stars beyond our Solar System. The discoveries made through these images mark critical first steps toward untangling the complexities of red giant stars.