Astronomers Just Found a Star System That Shouldn’t Exist Near a Supermassive Black Hole

A team of astronomers has found the first binary star system, D9, near the supermassive black hole Sagittarius A*.

Previously, scientists thought such systems couldn’t exist in this turbulent region. D9 is expected to merge into a single star soon, offering clues about the formation of young stars in this extreme environment.

First-Ever Binary Star Near a Supermassive Black Hole

An international team of researchers, led by PD Dr. Florian Peißker, has discovered the first binary star system near the supermassive black hole Sagittarius A* (Sgr A*) at the center of our galaxy. While most stars in the universe form in pairs or groups, only five binary star systems have been confirmed near Sgr A*, and all are located at a greater distance. This newly identified system, named D9, is the closest yet. Scientists believe that D9 will eventually merge into a single star in the near future.

The findings, published in Nature Communications under the title “A binary system in the S cluster close to the supermassive black hole Sagittarius A*,” provide new insights into the extreme conditions surrounding the Milky Way’s central black hole.

Observing the Stars Near Sgr A*

For the past 30 years, astronomers have used infrared telescopes to observe individual stars near Sgr A*. However, these observations have often raised more questions than answers. The central region of the galaxy is densely packed with millions of stars and is divided into different sub-regions.

One particularly intriguing area is the S star cluster, home to Sgr A*. Given the cluster’s high density, astronomers have long suspected it should contain multiple binary stars. Yet, until now, none had been detected in this region, with the previously known binary systems located farther from the black hole.

A Harsh Environment for Binary Stars

Researchers attributed this to gravitational forces: The stars in the S star cluster move in stable orbits around the black hole, similar to the Earth orbiting the Sun. However, the conditions there are much more extreme, as Sgr A* is four million times heavier than our sun. The stars therefore can reach speeds of several thousand kilometres per second, making it an unfavourable environment for the formation of binary star systems.

A New Approach Leads to a Breakthrough

The researchers discovered D9 by taking a different approach to observing certain dust sources in the S star cluster. Normally, several individual observations over the course of a year are superimposed and added together to amplify the signal of the objects.

“Nobody has looked closely at individual observations of the dust sources each night,” said Florian Peißker from the University of Cologne’s Institute of Astrophysics. “That was the crux of our study: investigating and analysing every single night. The data from the recordings is noisier, but still good enough. This is how we identified the binary star.”

Implications for Star Formation

The discovery of D9 now opens up the possibility for researchers to investigate the processes of star formation in more detail, as the system is very likely to merge in the coming decades to millennia and thus form a new, slightly heavier star. This would solve another mystery. Because the stars in the S star cluster close to the supermassive black hole are younger than any star cluster theory has predicted. The presence of the binary star system could therefore provide new clues as to how the stars form around the central black hole. The researchers assume that some of the young stars formed from binary star systems that had previously migrated from the area of the ‘inner parsec’ to the supermassive black hole.

Solving a Cosmic Mystery

Co-author Dr. Michael Zajaček from Masaryk University in Brno, Czech Republic, said: “Until now, it was a mystery how such young stars could form so close to Sgr A*, which in principle should prevent any gravitational collapse that is necessary for star formation. The discovery of this binary star system will significantly expand our knowledge regarding star formation.”

Dr. Emma Bordier, co-author and postdoc in the Collaborative Research Centre 1601 ‘Habitats of Massive Stars across Cosmic Time’ at the University of Cologne, added: “Different generations of Very Large Telescope instruments were used for these observations. The new findings clearly demonstrate how the combination of archival data and recent observations can complement each other to enable innovative studies and lead to exciting discoveries.”

Reference: “A binary system in the S cluster close to the supermassive black hole Sagittarius A*” by Florian Peißker, Michal Zajaček, Lucas Labadie, Emma Bordier, Andreas Eckart, Maria Melamed and Vladimír Karas, 17 December 2024, Nature Communications.
DOI: 10.1038/s41467-024-54748-3

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