On strong mass segregation around a massive black hole: Implications for lower-frequency gravitational-wave astrophysics

Understand

We present, for the first time, a clear $N$-body realization of the {\it strong mass segregation} solution for the stellar distribution around a massive black hole.

• We compare our $N$-body results with those obtained by solving the orbit-averaged Fokker-Planck (FP) equation in energy space.
• The $N$-body segregation is slightly stronger than in the FP solution, but both confirm the {\it robustness} of the regime of strong segregation when the number fraction of heavy stars is a (realistically) small fraction of the total population.
• In view of recent observations revealing a dearth of giant stars in the sub-parsec region of the Milky Way, we show that the time scales associated with cusp re-growth are not longer than $(0.1-0.25) \times T_{rlx}(r_h)$.