An international team has found that the IRS13 star cluster near our galaxy’s central black hole is surprisingly young. The discovery, made possible through decades of data and the James Webb Space Telescope, challenges current star formation theories and offers insights into the history and future of our galaxy’s center.
An international team led by Dr. Florian Peißker at the University of Cologne’s Institute of Astrophysics has taken a detailed look at a young star cluster near the supermassive black hole Sagittarius A* (Sgr A*) in our galaxy’s center. Surprisingly, they found that this cluster, IRS13, is much younger than anticipated.
Discovered over twenty years ago, only recently has it been possible able to identify the cluster’s specific members. They achieved this by combining a diverse array of data from multiple telescopes gathered over several decades.
The stars in the cluster are a mere few hundred thousand years old, exceptionally young by stellar standards, especially when compared to our 5 billion-year-old sun. Intriguingly, given the high-energy radiation and the galaxy’s tidal forces, it shouldn’t be possible for so many young stars to exist near the supermassive black hole.
This research, titled “The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. I. Detection of a Rich Population of Dusty Objects in the IRS13 Cluster,” has been published in The Astrophysical Journal.
James Webb Space Telescope’s Findings
In relation to this study, another significant discovery was made using the James Webb Space Telescope (JWST). For the first time, the JWST produced a spectrum of the Galactic Center that is free from atmospheric interference. This feat was made possible thanks to a prism developed at the Institute of Astrophysics, under the supervision of Professor Dr. Andreas Eckart, who is a co-author of this research. The resulting spectrum revealed the presence of water ice at the Galactic Center. This water ice, commonly found around young stellar objects, serves as further evidence supporting the young age of some stars near the black hole.
The Turbulent History of IRS13
Further insights from Dr. Peißker’s team suggest that IRS13 has undergone a complex formation history. It appears that IRS13 migrated toward the supermassive black hole, influenced by factors such as friction with the interstellar medium, collisions with other star clusters, or its internal dynamics. At some point, the black hole’s gravity “captured” the cluster. This gravitational interaction likely resulted in a bow shock formation at the cluster’s forefront, resembling a ship’s tip cutting through water. The resulting spike in dust density might have then triggered further star formation, which could explain why the cluster’s youngest stars are primarily at its top or front.
Deciphering Stellar Mysteries
“The analysis of IRS13 and the accompanying interpretation of the cluster is the first attempt to unravel a decade-old mystery about the unexpectedly young stars in the Galactic Center,” according to Dr. Peißker. “In addition to IRS13, there is a star cluster, the so-called S-cluster, which is even closer to the black hole and also consists of young stars. They are also significantly younger than would be possible according to accepted theories.”
The findings on IRS13 provide the opportunity for further research to establish a connection between the direct vicinity of the black hole and regions several light years away.
Dr. Michal Zajaček, second author of the study and scientist at Masaryk University in Brno (Czech Republic), added: “The star cluster IRS13 seems to be the key to unraveling the origin of the dense star population at the center of our galaxy. We have gathered extensive evidence that very young stars within the range of the supermassive black hole may have formed in star clusters such as IRS13. This is also the first time we have been able to identify star populations of different ages – hot main sequence stars and young emerging stars – in the cluster so close to the center of the Milky Way.”
Reference: “The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. I. Detection of a Rich Population of Dusty Objects in the IRS 13 Cluster” by Florian Peißker, Michal Zajaček, Lauritz Thomkins, Andreas Eckart, Lucas Labadie, Vladimír Karas, Nadeen B. Sabha, Lukas Steiniger and Maria Melamed, 10 October 2023, The Astrophysical Journal.