Indian Astronomers Capture Rare Star Being Rejuvenated

The research focused on a binary star system known as TIC 327546480, located in the ancient open star cluster Collinder 261, about 9,500 light-years from Earth.

Astronomers from the Indian Institute of Astrophysics (IIA), working with international collaborators, have made a rare discovery that sheds new light on one of astronomy's longest-standing mysteries. The team has identified a Blue Straggler Star (BSS) in the process of forming, providing some of the strongest direct evidence yet of how these unusual stars are created.

Blue Straggler Stars have puzzled scientists for decades because they appear younger, hotter and brighter than other stars in the same star cluster, despite all the stars having formed at roughly the same time. Researchers have widely believed that these stars gain new life by receiving material from a companion star or through stellar mergers, though clear observational proof has been difficult to obtain.

Rare binary system reveals the process in action

The research focused on a binary star system known as TIC 327546480, located in the ancient open star cluster Collinder 261, about 9,500 light-years from Earth. Scientists combined high-precision observations from NASA's Transiting Exoplanet Survey Satellite (TESS) with radial velocity measurements collected by the European Southern Observatory's Very Large Telescope in Chile.

The study revealed that one of the stars has expanded beyond its gravitational boundary, known as the Roche lobe, allowing material to flow toward its companion. This continuous transfer of matter is causing the companion to grow more massive, hotter and brighter, effectively transforming it into a Blue Straggler Star.

The researchers also detected strong X-ray emissions from the system, providing additional evidence that the mass transfer process is actively taking place.

Detailed observations strengthen the findings

The team found that the Blue Straggler has a mass about 1.67 times that of the Sun, while its companion has only 0.32 solar masses. The two stars orbit each other every 2.11 days, and the Blue Straggler spins rapidly at nearly 70 kilometres per second, a speed believed to result from the material it has accumulated over billions of years.

Evolutionary models suggest that the transfer of matter began around 5.46 billion years ago and is still continuing today, while the surrounding star cluster is estimated to be about 7 billion years old.

A breakthrough for stellar evolution research

Researchers say the discovery provides one of the clearest confirmations that Blue Straggler Stars can form through mass transfer in binary systems, helping resolve a question that has challenged astronomers for many years.

Beyond explaining the origin of these unusual stars, the system offers scientists a valuable opportunity to study how interacting stars evolve over time. The findings are expected to improve understanding of stellar evolution, binary star systems and the life cycles of star clusters across the universe.

The research has been published in The Astrophysical Journal Letters, with contributions from scientists at the Indian Institute of Astrophysics, Gauhati University, IUCAA Pune and research institutions in Italy, France and the United States.