The distribution of stars around the Milky Way's black hole III: Comparison with simulations

TL;DR

This study uses direct N-body simulations to reconcile the observed deficit of bright giants near the Milky Way's black hole with theoretical predictions of a stellar cusp, showing good agreement with recent observations.

Contribution

The paper presents the first direct N-body simulation results that match observed stellar distributions around the Milky Way's black hole, resolving a long-standing discrepancy.

Findings

Simulations show a power-law stellar distribution with slope ~0.3.

Observed giant star depletion within a few arcseconds of Sgr A* is explained by stellar collisions.

A stellar cusp likely exists in the innermost regions, hidden by collisional depletion.

Abstract

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 GC's 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.