Sagittarius B2, the Most Massive Star-Forming Region in the Milky Way

Sagittarius B2 (Sgr B2) is the largest and most active star-forming region in the Milky Way, located just a few hundred light-years from the supermassive black hole, Sagittarius A*, at our galaxy’s centre. This giant molecular cloud spans about 150 light-years and contains enough material to form approximately three million Sun-like stars. Despite holding only about 10% of the gas present in the galactic centre, it creates 50% of the stars in that region, making its star formation rate remarkably high compared to its surroundings, a mystery that astronomers are actively investigating with new observations.
 
Sagittarius B2 consists of three main dense cores: North, Main/Middle, and South. These cores are sites of extremely prolific star formation, containing regions dense enough that even the powerful James Webb Space Telescope’s (JWST) infrared instruments cannot see through them. Much of the starlight is obscured by thick molecular clouds, which also act as the raw material for new generations of stars. The ongoing research is focused on understanding what drives such an intense burst of star formation in Sgr B2 compared to its surroundings. Recently, JWST has imaged Sagittarius B2 in unprecedented detail, revealing a complex tapestry of newborn stars embedded in glowing gas and dust. These images show not just the visible stars but also the dark, dense regions where stars are still forming and hidden from view by thick clouds. One particularly bright and molecularly rich region, Sgr B2 North, stands out as a key zone of interest for understanding massive star formation processes.
 
Sagittarius B2’s proximity to the galactic centre, high density, mass (about 3 million solar masses), and extreme star formation, make it a primary laboratory for studying stellar birth in environments not unlike those of early, rapidly evolving galaxies. The peculiar efficiency of star formation there may be tied to environmental factors like concentrated gas, turbulent dynamics, or magnetic fields, all now being explored with advanced telescopes. Environmental factors at the galactic centre, such as strong gravitational interactions, intense radiation fields, and the effect of magnetic fields channelling gas into hot spots, appear to boost the star formation efficiency in Sgr B2 far above other regions. Moreover, sharp boundaries within the cloud detected by JWST suggest that an external event, like a past supernova, may have compressed the gas and further accelerated star formation. These unique conditions make Sagittarius B2 an exceptional and unusually productive stellar nursery within our galaxy.
 
Sagittarius B2 stands as a cornerstone for astrophysical studies of star formation, molecular cloud chemistry, and galaxy evolution near supermassive black holes.
 
References
(2025, October 2). Sagittarius B2, In Wikipedia, https://en.wikipedia.org/wiki/Sagittarius_B2

​(2025, September 24). NASA’a Webb Explores Largest Star-Forming Cloud in Milky Way. Jet Propulsion Laboratory. https://www.jpl.nasa.gov/news/nasas-webb-explores-largest-star-forming-cloud-in-milky-way/
 
(2025, September 24). James Webb Telescope Unveils Sagittarius B2 Star-Forming Cloud. James Webb Space Telescope. https://www.jameswebbdiscovery.com/discoveries/james-webb-telescope-unveils-sagittarius-b2-star-forming-cloud