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Astronomers from the Indian Institute of Astrophysics (IIA), with international collaborators, reported catching a Blue Straggler Star (BSS) actively forming in the binary system TIC 327546480 within the old open star cluster Collinder 261, about 9,500 light-years away.
The study combined high-precision light curves from NASA's TESS space mission with radial-velocity data from the European Southern Observatory's Very Large Telescope (VLT) in Chile, finding the BSS (about 1.67 solar masses) actively accreting matter from a smaller companion star (about 0.32 solar mass).
Strong X-ray emission from the system provided independent evidence of ongoing mass transfer, offering direct observational support for one of the leading theories of BSS formation — rejuvenation via mass transfer in a semidetached binary.
The findings, first-authored by Gauhati University PhD student and DST INSPIRE Fellow Ali Hasan Sheikh, were published in the Astrophysical Journal Letters.
BSS are stars found in star clusters that appear hotter, brighter and more massive than other cluster members of the same age — they sit above the cluster's expected evolutionary track, looking anomalously 'young'. Two accepted formation channels explain this: (1) mass transfer from a companion star via Roche-lobe overflow in a semidetached binary system, and (2) stellar mergers or collisions, common in dense cluster cores. Direct observational evidence of a BSS actively forming — rather than inferred after the fact — is extremely rare; this Collinder 261 system is one of the clearest such examples identified so far.
Simple Analogy: A blue straggler is like someone who suddenly looks decades younger because they've been 'borrowing' vitality from someone else — astronomers caught this borrowing (mass transfer) happening in real time in this system.
Autonomous research institute conducting research in astronomy, astrophysics and allied physics; wholly funded by the Department of Science & Technology (DST)
Nodal central department funding IIA and administering the INSPIRE Programme, under whose Fellowship component the study's first author is supported
Launched in April 2018 to survey about 200,000 nearby bright stars for transiting exoplanets; its high-precision light curves were combined with VLT radial-velocity data to characterise this BSS system
Launched in 2008 to attract young Indian talent to research careers via three components — Fellowship, Scholarship for Higher Education (SHE), and Faculty Fellowship; its doctoral Fellowship component supports the study's first author, Ali Hasan Sheikh
GS Paper 3 > Science & Technology > Space & Astronomy
Occasional — Indian-led astrophysics discoveries surface a few times a year and are increasingly tested for institution/mission static facts.
A star in a cluster that appears hotter, brighter and more massive than cluster members of the same age, formed via mass transfer from a companion or stellar collision/merger.
The gravitational boundary around a star in a binary system, beyond which its outer material is pulled toward the companion star.