Secular Dynamical Anti-Friction in Galactic Nuclei

Abstract

We identify a gravitational-dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole (SMBH). We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as "secular-dynamical anti-friction" (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity, (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration, and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

8 pages, 7 figures, Published in ApJ

References in corpus (7)

• The structure of the nuclear stellar cluster of the Milky Way
• Kinematics of the old stellar population at the Galactic Center
• Interaction of massive black hole binaries with their stellar environment: III. Scattering of bound stars
• Dynamical friction of massive objects in galactic centres
• Resonant relaxation near a massive black hole: the dependence on eccentricity
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• Effects of Intermediate Mass Black Holes on Nuclear Star Clusters
• Galaxy Rotation and Supermassive Black Hole Binary Evolution
• The Link Between Ejected Stars, Hardening and Eccentricity Growth of Super Massive Black Holes in Galactic Nuclei
• On the origin of the B-stars in the Galactic center
• The Thermodynamics of Rotating Black-Hole Star Clusters
• Formation of Dark Matter Torii Around Supermassive Black Holes Via The Eccentric Kozai-Lidov Mechanism
• The Coupling of Galactic Dark Matter Halos with Stellar Bars
• Mapping the Galactic centre's dark cluster via Resonant Relaxation
• The secular evolution of discrete quasi-Keplerian systems. II. Application to a multi-mass axisymmetric disc around a supermassive black hole
• Galactic merger implications for eccentric nuclear disks: a mechanism for disk alignment
• Probabilistic eccentricity bifurcation for stars around shrinking massive black hole binaries
• Resonant Dynamical Friction in Nuclear Star Clusters: Rapid Alignment of an Intermediate-mass Black Hole with a Stellar Disk