Science for All | Scientists discover a binary star system near Milky Way’s supermassive black hole

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Until now, scientists believed that there was no binary star system near Sagittarius A*, which is a supermassive black hole located at the centre of our Milky Way. However, new research suggests that one such system with the gravitationally bound stars is present in the S cluster, which is a group of high-velocity stars around Sagittarius A*.

The findings were published in Nature Communications journal on Tuesday, December 17, 2024.

Scientists have named this system D9 and it has similarities to G objects, which are strange celestial objects that “look like gas but behave like stars”. The study also predicts a lifespan of around three million years, before the stars merge into each other, because of their ongoing interaction with Sagittarius A*.

The two stars in the D9 system complete an orbit in around 372 days. This orbit, given their sizes, is just stable enough so that the overwhelming gravity of the black hole does not tear them apart. They are also approximately 1.59 astronomical units (AU) apart, which is well below the tidal disruption radius of approximately 42.4 AU. Tidal disruption radius is the distance which allows a star to be torn away by the supermassive black hole, causing a tidal disruption event.

The two stars in the D9 system are a Herbig Ae/Be star, and a T-Tauri star.

The discovery suggests that even though this binary system was previously undetected, such stars can survive in S clusters in the vicinity of supermassive black holes for long periods of time – around a million years for Sagittarius A*.

It is also important because the presence of a binary system alongside G objects allows us to partly resolve the “uncertain nature” of G objects. As the D9 system is predicted to merge, it may be possible that these G objects were binary systems that merged.