Evolution of Supermassive Black Hole Binary and Acceleration of Jet Precession in Galactic Nuclei

Abstract

Supermassive black hole binary (SMBHB) is expected with the hierarchical galaxy formation model. Currently, physics processes dominating the evolution of a SMBHB are unclear. An interesting question is whether we could observationally determine the evolution of SMBHB and give constraints on the physical processes. Jet precession have been observed in many AGNs and generally attributed to disk precession. In this paper we calculate the time variation of jet precession and conclude that jet precession is accelerated in SMBHB systems but decelerated in others. The acceleration of jet precession $dP_{\rm pr} / dt$ is related to jet precession timescale $P_{\rm pr}$ and SMBHB evolution timescale $τ_{\rm a}$, ${dP_{\rm pr} \over dt} \simeq - Λ{P_{\rm pr} \over τ_{\rm a}}$. Our calculations based on the models for jet precession and SMBHB evolution show that $dP_{\rm pr} / dt$ can be as high as about $- 1.0$ with a typical value -0.2 and can be easily detected. We discussed the differential jet precession for NGC1275 observed in the literature. If the observed rapid acceleration of jet precession is true, the jet precession is due to the orbital motion of an unbound SMBHB with mass ratio $q\approx 0.76$. When jets precessed from the ancient bubbles to the currently active jets, the separation of SMBHB decrease from about $1.46 {\rm Kpc}$ to $0.80 {\rm Kpc}$ with an averaged decreasing velocity $da/dt \simeq - 1.54 \times 10^6 {\rm cm/s}$ and evolution timescale $τ_{\rm a} \approx 7.5\times 10^7 {\rm yr}$. However, if we assume a steady jet precession for many cycles, the observations implies a hard SMBHB with mass ratio $q\approx 0.21$ and separation $a\approx 0.29 {\rm pc}$.