A team of astronomers from various institutions have made the world’s first confirmed discovery of a blue straggler star hosting a brown dwarf companion in a very compact binary system.

This breakthrough by the team from the Indian Institute of Astrophysics (IIA), Aryabhatta Research Institute of Observational Sciences (ARIES), Gauhati University, and INAF-Catania Astrophysical Observatory, Italy, could reshape astronomers’ understanding of how stars evolve.

Brighter and bluer

According to the Department of Science and Technology, scientists have long been puzzled by blue straggler stars, which appear brighter and bluer than the main-sequence turn-off in star clusters, defying standard stellar evolution because all cluster stars are expected to be of similar age.

The team consisted of Ali Hasan Sheikh, Biman J. Medhi from Gauhati University, Sergio Messina from INAF-Catania, Annapurni Subramanium and Ram Sagar from IIA, and Neelam Panwar from ARIES. They found that the system has an exceptionally short orbital period of around 5.6 hours (0.234 days) and contains the lightest companion ever detected around a blue straggler, with a mass of approximately 0.056 times the mass of the Sun, placing it firmly below the hydrogen-burning limit.

The study published in the journal ‘Monthly Notices of the Royal Astronomical Society: Letters’ reveals the shortest-period binary system discovered inside the so-called “brown dwarf desert”, a region where such companions are thought to be extremely rare.

Accurate models

“The rapidly rotating blue straggler star, accompanied by a substellar brown dwarf, that the researchers spotted is an object too massive to be a planet but too small to ignite as a true star. The study advances fundamental scientific knowledge by improving our understanding of how stars evolve, interact, and survive extreme environments, which is essential for building accurate models of stellar and cosmic evolution,” the Department said.

It added that the results help refine theoretical models of stellar evolution, binary interactions, and substellar objects, which are widely used in interpreting data from ground-based observatories and space missions.