On the distribution of stellar remnants around massive black holes: slow mass segregation, star cluster inspirals, and correlated orbits

Antonini, Fabio ORCID: https://orcid.org/0000-0003-3138-6199 2014. On the distribution of stellar remnants around massive black holes: slow mass segregation, star cluster inspirals, and correlated orbits. Astrophysical Journal 794 (2) , 106. 10.1088/0004-637X/794/2/106

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Abstract

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 gsim 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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Astronomical Society
ISSN:	0004-637X
Date of First Compliant Deposit:	19 February 2020
Date of Acceptance:	13 August 2014
Last Modified:	05 May 2023 09:45
URI:	https://orca.cardiff.ac.uk/id/eprint/129845

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