ALMA Discovers Companion Orbiting Red Giant Star π 1 Gruis

A team of international scientists has successfully identified a companion star orbiting the red giant star known as π 1 Gruis, located approximately 530 light-years from Earth. Utilizing advanced observational techniques through the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the researchers have unveiled significant insights into the dynamics of this celestial system, challenging existing models of stellar evolution.

Unraveling Stellar Mysteries

The red giant star, π 1 Gruis, is classified as an asymptotic giant branch (AGB) star, a stage in stellar evolution characterized by significant changes. Once similar to the sun, π 1 Gruis has expanded to over 400 times the sun’s size and now emits light thousands of times brighter than our sun. This extreme luminosity complicates the detection of any close companion stars, which can easily be outshone.

In a groundbreaking paper published in the journal Nature Astronomy, the team, including Yoshiya Mori, a Ph.D. candidate in astrophysics at Monash University, provided direct observational evidence of the companion’s orbit. Mori highlighted the importance of accurately determining the mass of π 1 Gruis to understand the companion’s influence, stating, “A key part of understanding the orbit of the companion is knowing the mass of the AGB star.”

Revising Stellar Evolution Models

The research presented a notable deviation from previous predictions. While earlier models suggested that the companion star would have an elliptical orbit, observations revealed an almost circular path. This finding implies that the orbital evolution may occur more rapidly than previously understood, prompting a reevaluation of how companions interact with giant stars.

Project lead Mats Esseldeurs 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 said.

The findings suggest that existing models may have underestimated the rates at which orbits circularize. This revelation opens new avenues for research into tidal interactions and the behavior of binary stars, potentially altering our understanding of the life cycles of stars and their companions.

The international collaboration showcases the significance of utilizing sophisticated technology to explore the cosmos. As scientists continue to investigate the complexities of stars like π 1 Gruis, the knowledge gained will enhance our comprehension of stellar life cycles and their implications for planetary systems.

The research, published on November 14, 2025, marks a milestone in astrophysics, offering insights that could reshape established theories and deepen our understanding of the universe. For further details, refer to the publication: Mats Esseldeurs et al, “Evidence for the Keplerian orbit of a close companion around a giant star,” in Nature Astronomy.