Nuclear Star Clusters in the Vicinity of Black hole
Adaptive optics spectroscopy has allowed for spectral identifications of bright stars within ~1 pc of the supermassive black hole and has revealed two very unexpected results. The first surprise was the detection of a wealth of young (<10 Myr) stars in a region where none were expected due to the strong tidal field of the black hole and the low present-day gas densities. The second surprise was the unanticipated dearth of late-type stars near the black hole.
A young (4-8 Myr) nuclear cluster surrounds the Galactic Center black hole and extends out to a radius of 0.5 pc. What is their formation history? This is an essential question in the study of the co-evolution and growth of Super Massive Black Hole and the nuclear star clusters that surround them.
The origin of young stars, where and when the clusters formed, is difficult to explain since the gas densities observed today are orders of magnitude too low for a gas clump to overcome the extreme tidal forces and collapse to form stars.
The star clusters' proximity should cause them to be torn apart, and thus their presence within the strong tidal field of our Galaxy's central SMBH still remains a puzzle.
If the star clusters formed in situ, then the events leading up to its formation were likely unique and extreme compared to those found in the local solar neighborhood.
For further reading:
• Do et al 2013 Three-dimensional Stellar Kinematics at the Galactic Center: Measuring the Nuclear Star Cluster Spatial Density Profile, Black Hole Mass, and Distance
• Do et al 2011 Testing Stellar Cusp Formation Theories with Observations of the Milky Way Nuclear Star Cluster