Astronomers discover an actively forming luminous blue straggler star

Key Highlights:

• Indian astronomers, with international collaborators, discovered a Blue Straggler Star (BSS) actively forming in a binary system.
• This finding provides direct observational evidence for the formation mechanism of BSSs through mass transfer.
• The system, TIC 327546480, is located in the old open star cluster Collinder 261, approximately 9500 light-years away.
• Observations utilized data from NASA's TESS space mission and the European Southern Observatory's Very Large Telescope.
• The research was published in the Astrophysical Journal Letters, with contributions from the Indian Institute of Astrophysics (IIA).

Detailed Insights:

• Blue Straggler Stars (BSS) are hotter, brighter, and more massive than their peers in star clusters, puzzling astronomers for decades.
• The most accepted theory for BSS formation is rejuvenation through mass gain from a companion star or stellar mergers.
• The discovered binary system is semidetached, meaning one star overflows its Roche Lobe, transferring material to the other.
• This ongoing mass transfer from a less massive companion to the BSS confirms the rejuvenation process is active.
• Strong X-ray emission from the system further supports the active mass transfer and accretion of material.
• The BSS has a mass of about 1.67 solar masses, accreting from a companion of 0.32 solar masses, with an orbital period of 2.11 days.
• Evolutionary modeling suggests mass transfer began around 5.46 billion years ago, while the cluster is about 7 billion years old.
• This discovery offers a unique laboratory to test theories of binary evolution and stellar rejuvenation.

Scientific/Technical Concepts Involved:

• Blue Straggler Star (BSS): A star in a cluster that appears younger, hotter, and more massive than expected for its age.
• Binary Star System: A system of two stars orbiting a common center of mass, often interacting gravitationally.
• Roche Lobe: The region around a star in a binary system within which orbiting material is gravitationally bound to that star.
• Mass Transfer: The flow of matter from one star to another in a close binary system, often when one star expands beyond its Roche Lobe.