Detection of an excess of young stars in the Galactic Centre Sagittarius B1 region

Abstract

The Milky Way’s centre is the closest galaxy nucleus and the most extreme environment in the Galaxy. Although its volume is less than 1% of that of the Galactic Disk, up to 10% of all new stars in the Galaxy in the past 100 Myr formed there. It therefore constitutes a perfect laboratory to understand star formation under extreme conditions, similar to those in starburst or high-redshift galaxies. However, the only two known young clusters in the Galactic Centre account for <10% of the expected young stellar mass. We analyse the star formation history of Sagittarius (Sgr) B1, a Galactic Centre region associated with strong H ii emission, and find evidence for the presence of several 105 solar masses of young stars that formed ~10 Myr ago. We also detect the presence of intermediate-age (2–7 Gyr old) stars in Sgr B1 that seem to be rare (or absent) in the inner regions of the nuclear stellar disk, and might indicate inside-out formation. Our results constitute a large step towards a better understanding of star formation at the Galactic Centre, such as the fate of young clusters, and the possibly different initial mass function in this region.