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Blue Straggler Star (BSS) Context Indian astronomers from the Indian Institute of Astrophysics (IIA), along with international collaborators, have reported the rare discovery of a Blue Straggler Star (BSS) actively forming in the binary star system TIC 327546480. The finding provides one of the clearest direct observations of how Blue Straggler Stars are created through ongoing mass transfer. Blue Straggler Stars (BSS) What is a Blue Straggler Star? A Blue Straggler Star (BSS) is an unusually hot, luminous, blue, and massive star found in old stellar populations, especially globular clusters and open clusters. Normally, stars of such high mass should have already exhausted their hydrogen fuel and evolved into red giants or white dwarfs. However, Blue Stragglers appear much younger, brighter, and hotter than neighbouring stars that were born at the same time, making them appear to "straggle behind" in the normal course of stellar evolution. Discovery • First identified: 1953 • Astronomer: Allan Sandage • Location: Globular Cluster M3 The discovery challenged conventional theories of stellar evolution and led astronomers to investigate mechanisms capable of rejuvenating ageing stars. Formation of Blue Straggler Stars Blue Stragglers are believed to form when an ageing star receives a fresh supply of hydrogen-rich material, effectively resetting its nuclear clock. 1. Mass Transfer in Binary Systems (Most Common) In a close binary system: • As one star ages, it expands into a Red Giant. • It overflows its Roche lobe (the region where its gravity dominates). • Hydrogen-rich gas flows to its companion through Roche Lobe Overflow (RLOF). • The companion gains mass, becomes hotter, brighter and bluer, and begins rotating rapidly. • The rejuvenated companion becomes a Blue Straggler Star. The newly discovered system TIC 327546480 is a direct example of this process in action. 2. Stellar Collision or Merger In the dense cores of globular clusters: • Two stars may collide or merge. • Their combined mass creates a single more massive and hotter star. • The merged star behaves like a young star, despite being billions of years old.