Evolution of Stellar Orbits Around Merging Massive Black-Hole Binary

Abstract

We study the long-term orbital evolution of stars around a merging massive or supermassive black-hole (BH) binary, taking into account the general relativistic effect induced by the BH spin. When the BH spin is significant compared to and misaligned with the binary orbital angular momentum, the orbital axis ($\hat{\mathbf{l}}$) of the circumbinary star can undergo significant evolution during the binary orbital decay driven by gravitational radiation. Including the spin effect of the primary (more massive) BH, we find that starting from nearly coplanar orbital orientations, the orbital axes $\hat{\mathbf{l}}$ of circumbinary stars preferentially evolve towards the spin direction after the merger of the BH binary, regardless of the initial BH spin orientation. Such alignment phenomenon, i.e., small final misalignment angle between $\hat{\mathbf{l}}$ and the spin axis of the remanent BH $\hat{\mathbf{S}}$, can be understood analytically using the principle of adiabatic invariance. For the BH binaries with extremely mass ratio ($m_2/m_1\lesssim 0.01$), $\hat{\mathbf{l}}$ may experience more complicated evolution as adiabatic invariance breaks down, but the trend of alignment still works reasonably well when the initial binary spin-orbit angle is relatively small. Our result suggests that the correlation between the orientations of stellar orbits and the spin axis of the central BH could provide a potential signature of the merger history of the massive BH.

13 pages, 15 figures, accepted for publication in MNRAS

References in corpus (14)

• A Compact Supermassive Binary Black Hole System
• Massive black hole binary mergers within sub-pc scale gas discs
• Rapid Formation of Supermassive Black Hole Binaries in Galaxy Mergers with Gas
• Supermassive black hole binaries in gaseous and stellar circumnuclear discs: orbital dynamics and gas accretion
• A Candidate Sub-Parsec Supermassive Binary Black Hole System
• Suppression of extreme orbital evolution in triple systems with short range forces
• Steady-state planet migration by the Kozai-Lidov mechanism in stellar binaries
• Chandra unveils a binary Active Galactic Nucleus in Mrk463
• Mass-gap Mergers in Active Galactic Nuclei
• A close-pair binary in a distant triple supermassive black-hole system
• Constraining the Orbit of Supermassive Black Hole Binary 0402+379
• Inclination Evolution of Protoplanetary Disks Around Eccentric Binaries
• An upper limit on the spin of SgrA${}^{\ast }$ based on stellar orbits in its vicinity
• Secular Dynamics of an Exterior Test Particle: The Inverse Kozai and Other Eccentricity-Inclination Resonances