Indian Astronomers Capture Blue Straggler Star Formation in Rare Discovery
New Delhi, July 27 (TNT): Indian astronomers, along with international collaborators, have reported the rare discovery of a Blue Straggler Star (BSS) caught in the process of formation, providing direct observational evidence of how these unusual stars are created.
Blue Straggler Stars are a peculiar class of stars found in star clusters that appear hotter, brighter and more massive than other stars of similar age. Their origin has remained a long-standing mystery in stellar astrophysics, with scientists proposing that they form by gaining mass from companion stars or through stellar mergers.
A team of astronomers from the Indian Institute of Astrophysics (IIA), an autonomous institute under the Department of Science and Technology (DST), studied the binary star system TIC 327546480 located in the old open star cluster Collinder 261, around 9,500 light-years away.
The system was identified as a promising candidate due to signs of interaction between the two stars.
Researchers combined high-precision observations from NASA’s TESS space mission with radial velocity measurements obtained using the Very Large Telescope operated by the European Southern Observatory in Chile.
“We discovered that the Blue Straggler is actively gaining material from its companion star, providing a rare glimpse of a BSS caught in the act of formation,” said Annapurni Subramaniam, faculty member at IIA and co-author of the study.
The researchers found that the binary system is semi-detached, meaning one star has expanded beyond its gravitational boundary, known as the Roche lobe, allowing material to flow from the less massive companion to the Blue Straggler Star.
The ongoing mass transfer confirms that the rejuvenation process is still taking place, making the system one of the clearest examples of a forming Blue Straggler identified so far.
The team also detected strong X-ray emission from the system, which provides additional evidence that material transferred from the companion star is currently being absorbed by the Blue Straggler.
According to the study, the Blue Straggler has a mass of about 1.67 times that of the Sun and is accreting material from a companion star with a mass of around 0.32 solar masses. The binary system has an orbital period of 2.11 days, a mass ratio of approximately 0.19, and the Blue Straggler rotates rapidly at around 69.55 km per second.
Researchers said evolutionary modelling suggests that mass transfer began around 5.46 billion years ago and continues to the present, while the host star cluster is estimated to be around 7 billion years old.
“This discovery provides one of the strongest pieces of direct observational evidence yet for the formation of BSSs through mass transfer in binary systems,” said Ram Sagar, faculty member at IIA and co-author of the study.
The researchers said the discovery offers a unique opportunity to test theories of binary evolution and stellar rejuvenation, with implications for understanding the evolution of star clusters and interacting stars across the Universe.
The findings have been published in the Astrophysical Journal Letters.
The study was authored by researchers from the Indian Institute of Astrophysics, Gauhati University, IUCAA Pune, INAF Italy, LUX Observatoire de Paris, France, and the University of North Florida, USA.
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