On the distribution of stellar remnants around massive black holes: slow mass segregation, star cluster inspirals, and correlated orbits
- Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada)
We use N-body simulations as well as analytical techniques to study the long-term dynamical evolution of stellar black holes (BHs) at the Galactic center (GC) and to put constraints on their number and mass distribution. Starting from models that have not yet achieved a state of collisional equilibrium, we find that timescales associated with cusp regrowth can be longer than the Hubble time. Our results cast doubts on standard models that postulate high densities of BHs near the GC and motivate studies that start from initial conditions that correspond to well-defined physical models. For the first time, we consider the distribution of BHs in a dissipationless model for the formation of the Milky Way nuclear cluster (NC), in which massive stellar clusters merge to form a compact nucleus. We simulate the consecutive merger of ∼10 clusters containing an inner dense sub-cluster of BHs. After the formed NC is evolved for ∼5 Gyr, the BHs do form a steep central cusp, while the stellar distribution maintains properties that resemble those of the GC NC. Finally, we investigate the effect of BH perturbations on the motion of the GC S-stars as a means of constraining the number of the perturbers. We find that reproducing the quasi-thermal character of the S-star orbital eccentricities requires ≳ 1000 BHs within 0.1 pc of Sgr A*. A dissipationless formation scenario for the GC NC is consistent with this lower limit and therefore could reconcile the need for high central densities of BHs (to explain the S-stars orbits) with the 'missing-cusp' problem of the GC giant star population.
- OSTI ID:
- 22370426
- Journal Information:
- Astrophysical Journal, Vol. 794, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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