Constraining black hole parameters with the precessing jet nozzle of M87*

Abstract

Recently, Cui et al. [Nature \textbf{621}, 711 (2023)] reported that the jet nozzle of M87* exhibits a precession with a period of approximately 11 years. This finding strongly suggests that the supermassive black hole in the core of M87 galaxy is a spinning black hole with a tilted accretion disk. In this paper, our aim is to utilize these observations to preliminarily constrain the parameters of the black hole by using the characteristics of the geodesic motion. Firstly, we investigate the properties of the spherical orbits and the innermost stable spherical orbits with constant radius. The corresponding angular momentum, energy, and Carter constant for both prograde and retrograde orbits are calculated. We find that, compared to equatorial circular orbits, these quantities exhibit significant differences for fixed tilt angles. Moreover, the Carter constant takes positive values for nonvanishing tilt angles. Notably, the presence of misalignment of the orbit angular momentum and black hole spin leads to a precession effect in these spherical orbits. We then make use of these spherical orbits to model the warp radius of the tilted accretion disk, which allows us to determine the corresponding precession period through the motion of massive particles. Further comparing with the observation of M87*, the relationship between the black hole spin and the warp radius is given, through which if one of them is tested, the other one will be effectively determined. Additionally, our study establishes an upper bound on the warp radius of the accretion disk. These findings demonstrate that the precession of the jet nozzle offers a promising approach for testing the physics of strong gravitational regions near a supermassive black holes.