An international team of scientists has made a groundbreaking discovery by calculating the orbit of a companion around the asymptotic giant branch (AGB) star π1 Gruis. Utilizing the advanced capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA), this research marks a significant leap in understanding the dynamics of close companions to giant stars.
Located approximately 530 light-years from Earth, π1 Gruis is a red giant star that has intrigued astronomers for years. Known as an AGB star, π1 Gruis was once similar to our Sun but has since expanded to over 400 times its original size. Despite its brightness, detecting companions around such stars has been challenging due to their overwhelming luminosity.
Revealing the Mysteries of Giant Stars
The discovery of a companion orbiting π1 Gruis is pivotal in enhancing our understanding of the Keplerian motion of close companions to giant stars. These companions can significantly influence stellar evolution, yet direct observational evidence has been elusive until now.
Yoshiya Mori, a PhD candidate in Astrophysics at Monash University, played a crucial role in this research. By comparing observed properties of π1 Gruis with stellar evolution models, Mori and the team were able to better constrain the mass of the AGB star. This understanding is essential for accurately determining the orbit of its companion.
“A key part of understanding the orbit of the companion is knowing the mass of the AGB star. Our team helped better constrain this mass by using its observed luminosity and pulsation characteristics to find the best suited stellar model,” said Yoshiya Mori.
Implications for Stellar and Planetary Evolution
Contrary to earlier predictions of an elliptical orbit, the research revealed an almost perfectly circular orbit for the companion. This finding suggests that the orbit evolves more rapidly than previously thought, prompting a reevaluation of existing models related to the final life stages of giant stars with companions.
Mats Esseldeurs, the project lead from KU Leuven, emphasized the broader implications of this discovery. “Understanding how close companions behave under these conditions helps us better predict what will happen to the planets around the Sun, and how the companion influences the evolution of the giant star itself,” he stated.
“The analysis suggests that model predicted circularisation rates may have been underestimated. Researchers believe this will open avenues for our understanding of tidal interaction physics and binary evolution,” Esseldeurs added.
Collaborative Efforts and Future Research
This project was a collaborative effort involving KU Leuven, Monash University, CEA Paris-Saclay, and other international partners. The findings not only enhance our understanding of stellar and planetary evolution but also highlight the importance of international collaboration in advancing astronomical research.
The research paper detailing these findings has been published in Nature Astronomy, and it is expected to pave the way for further studies into the complex interactions between giant stars and their companions.
For more information, interested readers can access the research paper: https://doi.org/10.1038/s41550-025-02697-2
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This discovery not only enriches our understanding of stellar phenomena but also sets the stage for future explorations into the life cycles of stars and their companions, offering a glimpse into the eventual fate of our own solar system.
