A comment on the star density at the Galactic Centre, and the nature of infrared source sixteen

An analysis of high-resolution near infrared data shows that the power-law variation of star density $$(\rho_{\ast}(r) ^{\propto}_{\sim} \,r^{-1.8})$$ extends inwards to a central ‘core’ of radius $$R_\text{c} \lesssim 0.1 \,\text{pc}.$$ The core density is of order $$10^{7} M_{\odot} \,\text{pc}^{-3},$$ and IRS 16 can be understood quantitatively as due to projection of this highly centrally condensed star distribution. The very high star density has a number of important implications for theories of the Galactic Centre, and makes it possible to explain the observed inward increase of gas velocity dispersion on models not containing a massive black hole. Dynamical evolution of the central core is very rapid; the core collapse time-scale for the model described here is ~ 10⁹ yr. If a central constant-density ‘core’ has indeed been resolved, a rough upper limit to the mass of any black hole is $$M_\text{h} \lesssim M_\text{c} \lesssim 10^{5} M_{\odot}.$$