We report on the structure of the nuclear star cluster in the innermost 0.16 pc of the Galaxy as measured by the number density profile of late-type giants .
Using laser guide star adaptive optics in conjunction with the integral field spectrograph , OSIRIS , at the Keck II telescope , we are able to differentiate between the older , late-type ( \sim 1 Gyr ) stars , which are presumed to be dynamically relaxed , and the unrelaxed young ( \sim 6 Myr ) population .
This distinction is crucial for testing models of stellar cusp formation in the vicinity of a black hole , as the models assume that the cusp stars are in dynamical equilibrium in the black hole potential .
In the survey region , we classified 60 stars as early-type ( 23 newly identified ) and 74 stars as late-type ( 61 newly identified ) .
We find that contamination from young stars is significant , with more than twice as many young stars as old stars in our sensitivity range ( K ^ { \prime } < 15.5 ) within the central arcsecond .
Based on the late-type stars alone , the surface stellar number density profile , \Sigma ( R ) \propto R ^ { - \Gamma } , is flat , with \Gamma = -0.27 \pm 0.19 .
Monte Carlo simulations of the possible de-projected volume density profile , n ( r ) \propto r ^ { - \gamma } , show that \gamma is less than 1.0 at the 99.73 % confidence level .
These results are consistent with the nuclear star cluster having no cusp , with a core profile that is significantly flatter than predicted by most cusp formation theories , and even allows for the presence of a central hole in the stellar distribution .
Of the possible dynamical interactions that can lead to the depletion of the red giants observable in this survey – stellar collisions , mass segregation from stellar remnants , or a recent merger event – mass segregation is the only one that can be ruled out as the dominant depletion mechanism .
The lack of a stellar cusp around a supermassive black hole would have important implications for black hole growth models and inferences on the presence of a black hole based upon stellar distributions .