A team of Indian astronomers and international collaborators has discovered a rare Blue Straggler Star (BSS) actively undergoing formation, providing direct evidence of the process behind the creation of these unusual stars.
Blue Straggler Stars are a unique group of stars found in star clusters that appear younger, hotter, brighter and more massive than surrounding stars. Scientists believe they form by gaining mass from companion stars or through stellar mergers, but direct observations of this process have been extremely limited.
Researchers 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 study combined data from NASA’s TESS space mission with radial velocity observations from the European Southern Observatory’s Very Large Telescope in Chile. The observations revealed that the Blue Straggler Star is actively receiving material from its companion, providing rare evidence of a star being formed through mass transfer.
The researchers found the system to be a semidetached binary, where one star has expanded beyond its Roche lobe and is transferring matter to the Blue Straggler Star. Strong X-ray emissions from the system further confirmed that the mass transfer process is currently active.
The study revealed that the Blue Straggler Star has a mass about 1.67 times that of the Sun and is receiving material from a companion star with about 0.32 solar masses. The binary system has an orbital period of 2.11 days, while the Blue Straggler rotates rapidly due to the transferred material.
According to researchers, this discovery provides one of the strongest observational confirmations of the theory that Blue Straggler Stars can form through mass transfer in binary systems. The finding will help scientists better understand stellar evolution, star clusters and interactions between stars across the universe.
The research has been published in the Astrophysical Journal Letters and includes contributions from scientists from India, Italy, France and the United States.
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