An international team of scientists has successfully calculated the orbit of a companion around the asymptotic giant branch (AGB) star π1 Gruis. Utilizing the Atacama Large Millimeter/submillimeter Array (ALMA), this discovery marks a significant advancement in understanding the Keplerian motion of close companions to giant stars.
Located 530 light-years from Earth, π1 Gruis, affectionately known as “pi-one-Gru” among astronomers, has long intrigued scientists. As an AGB star, it was once similar to our Sun but has since expanded to over 400 times its size, becoming a red giant. This transformation has made it a luminous beacon, shining thousands of times more brightly than the Sun, complicating the detection of any close companions.
Unraveling the Mysteries of Giant Stars
AGB stars like π1 Gruis are crucial to our understanding of stellar evolution. They synthesize new elements, undergo pulsations over days to years, and lose significant mass before concluding their lives as planetary nebulae—ionized gas ejected from the star. Despite their importance, direct observational evidence of companions around such stars has been elusive until now.
In a recent publication in Nature Astronomy, the international team demonstrated the orbit of a companion using ALMA’s resolving power. This astronomical interferometer, comprising 66 radio telescopes in Chile’s Atacama Desert, provided the necessary precision for this groundbreaking research.
Scientific Insights and Implications
Yoshiya Mori, a PhD candidate in Astrophysics at Monash University, played a pivotal role by comparing observed properties of π1 Gruis with advanced stellar evolution models. “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,” Mori explained.
“This research is especially interesting, as throwing a close companion into the mix could possibly wreak further havoc on the already complicated processes surrounding these stars.”
Contrary to earlier predictions of an elliptical orbit, the research revealed an almost perfectly circular orbit for the companion. This finding suggests a faster orbital evolution than previously thought, prompting revisions to existing models of giant stars’ final life stages.
Future Implications for Stellar and Planetary Evolution
Project lead Mats Esseldeurs from KU Leuven highlighted the broader implications, noting that our Sun will eventually undergo a similar phase. “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, opening new avenues for understanding tidal interaction physics and binary evolution.
This collaborative project involved institutions such as KU Leuven, Monash University, and CEA Paris-Saclay, among others. The findings not only enhance our comprehension of stellar dynamics but also offer insights into the future of our solar system.
Looking Ahead
As researchers continue to refine their models and explore the implications of these findings, the study of AGB stars and their companions will remain a vibrant field of inquiry. The knowledge gained from π1 Gruis will undoubtedly inform future research and deepen our understanding of the universe’s complex mechanisms.
For those interested in the detailed findings, the research paper is available at Nature Astronomy.
