The distribution of stars around a massive black hole (MBH) has been addressed in stellar dynamics for the last four decades by a number of authors. Because of its proximity, the centre of the Milky Way is the only observational test case where the stellar distribution can be accurately tested. Past observational work indicated that the brightest giants in the Galactic Centre (GC) may show a density deficit around the central black hole, not a cusp-like distribution, while we theoretically expect the presence of a stellar cusp. We here present a solution to this long-standing problem. We performed direct-summation $N-$body simulations of star clusters around massive black holes and compared the results of our simulations with new observational data of the GCs nuclear cluster. We find that after a Hubble time, the distribution of bright stars as well as the diffuse light follow power-law distributions in projection with slopes of $Gamma approx 0.3$ in our simulations. This is in excellent agreement with what is seen in star counts and in the distribution of the diffuse stellar light extracted from adaptive-optics (AO) assisted near-infrared observations of the GC. Our simulations also confirm that there exists a missing giant star population within a projected radius of a few arcsec around Sgr A*. Such a depletion of giant stars in the innermost 0.1 pc could be explained by a previously present gaseous disc and collisions, which means that a stellar cusp would also be present at the innermost radii, but in the form of degenerate compact cores.
تحميل البحث