Indian astronomers, along with international collaborators, have reported the rare discovery of a Blue Straggler Star (BSS) caught in the process of formation, providing some of the strongest direct observational evidence yet for how these unusual stars are created.
The research team, led by scientists from the Indian Institute of Astrophysics (IIA), studied the binary star system TIC 327546480 in the Collinder 261 star cluster, located around 9,500 light-years from Earth.
Blue Straggler Stars are hotter, brighter, and more massive than other stars of a similar age within the same cluster, making them an enduring mystery for astronomers. The leading theory suggests they form by gaining mass from a companion star or through stellar mergers, but direct evidence of this process has remained rare.
Using high-precision observations from NASA’s TESS space mission together with radial velocity measurements from the European Southern Observatory’s Very Large Telescope in Chile, the researchers found that the system is semi-detached, with one star actively transferring material to the Blue Straggler.
The team also detected strong X-ray emissions, providing independent evidence that mass transfer is currently taking place. Their analysis showed the Blue Straggler has a mass about 1.67 times that of the Sun, while its companion is around 0.32 solar masses. The binary system completes an orbit every 2.11 days, and modelling indicates the mass-transfer process began approximately 5.46 billion years ago and continues today.
Researchers said the discovery offers a unique opportunity to study stellar rejuvenation and binary star evolution, explaining the formation of Blue Straggler Stars and improving understanding of the evolution of star clusters across the Universe. The findings have been published in The Astrophysical Journal Letters.
