Title: Discovery of a Dense Association of Stars in the Vicinity of the Supermassive Black Hole Sgr A*
Authors: S. Elaheh Hosseini, Andreas Eckart, Michal Zajaček, Silke Britzen, Harshitha K. Bhat, Vladimír Karas
First Author’s Institution: Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
Status: Published in the Astrophysical Journal (open access)
The Galactic Center is a dynamic region at the heart of our Milky Way galaxy, home to a supermassive black hole, Sgr A* (Sagittarius A-Star). It is densely packed with stars, gas, and dust, all interacting in fascinating ways. One challenge in studying this region is understanding the movement of stars, particularly those near the black hole, where gravitational forces are intense.
Astronomers have previously observed stars with unusual motions near Sgr A*, but a recent study highlights 42 sources near IRS 1W, an infrared source and well-known bow-shock source near the center of the Galaxy. These sources are moving northward towards Sgr A*, and their behavior offers new insights into the region’s dynamics. What do the distributions, origins, and potential connections of these stars reveal about the enigmatic region surrounding Sgr A*?
What are the N-sources?
The study identifies these 42 sources, referred to as the N-sources, as a group of stars moving northward relative to the central black hole. Their spatial distributions and proper motions reveal they are more clustered than stars in random regions at a similar distance from Sgr A*. This clustering, combined with their motion, suggests that the N-sources near the galaxy’s center may be part of a stellar association—a group of stars moving together in the same direction but not held together by gravity.
The authors also analyzed X-ray data from the Chandra X-ray Observatory, revealing no significant X-ray emission from the N-source region. In contrast, both the X-ray bright Sgr A* and IRS 13, another well-known infrared source near this region, show significant emission. This lack of X-ray emission from the N-sources adds complexity to understanding these sources and their origin.
Two Possible Origins
The study suggests two primary scenarios for the origin of the N-sources:
- A Stellar Cluster Around an Intermediate-Mass Black Hole (IMBH):
One possibility is that the N-sources are part of a stellar cluster that is stabilized by an intermediate-mass black hole (IMBH), a type of black hole with a mass between stellar-mass black holes and supermassive black holes like Sgr A*. The authors suggest the IMBH could have formed from stellar-mass black holes colliding with stars. If the N-sources are associated with this IMBH, their motion could be influenced by the gravitational forces of the IMBH, keeping the cluster intact in the dense environment of the Galactic Center. Data from the Chandra X-ray telescope suggest that this hypothetical IMBH would be surrounded by a faint accretion flow. Since weaker flows with less infalling material typically produce less X-ray radiation, this could explain the lack of bright X-ray emission at the N-source locations. - A Projection Effect from a Stellar Disk:
Alternatively, the N-sources and IRS 13, another stellar association, might simply appear clustered because of their position along the same stellar disk. This disk could be a projection of stars from a larger structure, such as the clockwise stellar disk observed in other regions near Sgr A*. In this case, the N-sources might not be physically bound to an IMBH but could just be stars from a local disk-like structure.
Looking Ahead: What’s Next for Studying the N-sources?
To better understand the N-sources’ origin, future spectroscopic observations, especially with the James Webb Space Telescope, will be crucial. These observations could provide key data on the stars’ velocities, helping astronomers determine whether they are part of a stellar cluster around an IMBH or just a projection from a larger stellar disk.
The study of the N-sources offers important insights into the dynamics of the Galactic Center, a region that is both an astrophysical laboratory and a challenging environment for astronomers. By understanding how stars move in this dense, gravitationally extreme region, researchers can learn more about the role of supermassive black holes, intermediate-mass black holes, and stellar clusters in shaping the structure and evolution of our galaxy.
Astrobite edited by Viviana Cáceres and Lucas Brown.
Featured image credit: “Las estrellas en la Vía Láctea” by Felix Mittermeier.
