Resonant Dynamical Friction in Nuclear Star Clusters: Rapid Alignment of an Intermediate-mass Black Hole with a Stellar Disk

Abstract

We investigate the dynamical evolution of an intermediate-mass black hole (IMBH) in a nuclear star cluster hosting a supermassive black hole (SMBH) and both a spherical and a flattened disk-like distribution of stellar-mass objects. We use a direct N-body (phiGPU) and an orbit-averaged (N-ring) numerical integrator to simulate the orbital evolution of stars and the IMBH. We find that the IMBH's orbit gradually aligns with the stellar disk if their mutual initial inclination is less than 90 degree. If it is larger than 90 degree, i.e. counterrotating, the IMBH does not align. Initially, the rate of orbital reorientation increases linearly with the ratio of the mass of the IMBH over the SMBH mass and it is orders of magnitude faster than ordinary (i.e. Chandrasekhar) dynamical friction, particularly for high SMBH masses. The semimajor axes of the IMBH and the stars are approximately conserved. This suggests that the alignment is predominantly driven by orbit-averaged gravitational torques of the stars, a process which may be called resonant dynamical friction. The stellar disk is warped by the IMBH, and ultimately increases its thickness. This process may offer a test for the viability of IMBH candidates in the Galactic Center. Resonant dynamical friction is not limited to IMBHs; any object much more massive than disk particles may ultimately align with the disk. This may have implications for the formation and evolution of black hole disks in dense stellar systems and gravitational wave source populations for LIGO, VIRGO, KAGRA, and LISA.

19 pages, 14 figures, 1 video, accepted by ApJ

References in corpus (28)

• An Update on Monitoring Stellar Orbits in the Galactic Center
• Intermediate mass black holes in AGN disks II. Model predictions & observational constraints
• On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening
• Large scale kinematics and dynamical modelling of the Milky Way nuclear star cluster
• Repeated mergers and ejection of black holes within nuclear star clusters
• The Milky Way's nuclear star cluster: Old, metal-rich, and cuspy
• The Globular Cluster Migratory Origin of Nuclear Star Clusters
• A numerical study of vector resonant relaxation
• Henize 2-10: the ongoing formation of a nuclear star cluster around a massive black hole
• Three Mechanisms for Bar Thickening
• On the rotation of nuclear star clusters formed by cluster-inspirals
• A semi-analytic dynamical friction model for cored galaxies
• Effects of Intermediate Mass Black Holes on Nuclear Star Clusters
• Millimetre-wave Emission from an Intermediate-Mass Black Hole Candidate in the Milky Way
• Cluster Core Dynamics at the Galactic Center
• Kinematic Structure of the Galactic Center S-cluster
• Global torques and stochasticity as the drivers of massive black hole pairing in the young Universe
• Indication of Another Intermediate-mass Black Hole in the Galactic Center
• A Self-Consistent, Time-Dependent Treatment of Dynamical Friction: New Insights regarding Core Stalling and Dynamical Buoyancy
• On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster
• The Second Galactic Center Black Hole?; A Possible Detection of Ionized Gas Orbiting around an IMBH embedded in the Galactic Center IRS13E complex
• Revealing the Formation of the Milky Way Nuclear Star Cluster via Chemo-Dynamical Modeling
• On the eccentricity evolution of massive black hole binaries in stellar backgrounds
• The Fifth Candidate for an Intermediate-mass Black Hole in the Galactic Center
• Star formation at the Galactic Centre: coevolution of multiple young stellar discs
• Dressed diffusion and friction coefficients in inhomogeneous multicomponent self-gravitating systems
• Resonant and non-resonant relaxation of globular clusters
• Galactic merger implications for eccentric nuclear disks: a mechanism for disk alignment