Scientists detect close companion orbiting giant red star

MELBOURNE, Nov. 14 (Xinhua) -- An international research team involving Australian scientists has been able to calculate the orbit of companions around a giant red star, offering new insight into how aging stars evolve toward the end of their lives.

Using the Atacama Large Millimeter/submillimeter Array in Chile, scientists observed the red giant star called π1 Gruis, located about 530 light-years from Earth, and identified a companion moving around it in an "almost perfectly round orbit," according to a Friday news release of Australia's Monash University, which conducted the study with KU Leuven in Belgium and other international partners.

Close companions influence stellar evolution in many ways. While some companions are detected around young stars, direct evidence of companions around asymptotic giant branch (AGB) stars or ageing stars has remained elusive, it said, adding the AGB star π1 Gruis, once like the Sun, is now an ageing star at the end of its life and has cooled and expanded to over 400 times its size, becoming a red giant.

Monash PhD Candidate in Astrophysics Yoshiya Mori said the team used stellar models to better estimate the mass and pulsation of π1 Gruis, which shines a few thousand times more brightly than the Sun, making detecting any close companion objects to these stars exceptionally difficult, since "they can outshine them and also vary in brightness."

Despite earlier predictions of an elliptical orbit for the companion star, the research has observed an almost perfectly round orbit, suggesting that the orbit evolves faster than previously thought, according to the study published in Nature Astronomy.

The result calls for adjustments to existing models of the final life stage of giant stars with companions, it said.

Our Sun will one day go through such a stage as well, said project lead, Mats Esseldeurs, from KU Leuven, adding, "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."

The analysis suggests that model-predicted circularization rates may have been underestimated, the release said, adding that researchers believe this will open avenues for understanding tidal interaction physics and binary evolution. Enditem