On the dynamics of tilted black hole-torus systems

TL;DR

This paper uses innovative tracer particles in 3D numerical relativity simulations to analyze the complex dynamics of tilted black hole-torus systems, revealing insights into precession, non-axisymmetric modes, and quasi-periodic oscillations similar to those observed in X-ray binaries.

Contribution

First application of tracer particles in 3D simulations of tilted black hole-torus systems, enabling detailed analysis of their complex dynamics and oscillation features.

Findings

Identification of black hole precession and non-axisymmetric modes.

Detection of quasi-periodic oscillations with frequencies matching observations.

Frequency ratio of QPO peaks around 1.9, inconsistent with simple p-mode models.

Abstract

We present results from three-dimensional, numerical relativity simulations of a {\it tilted} black hole-thick accretion disc system. The simulations are analysed using tracer particles in the disc which are advected with the flow. Such tracers, which we employ in these new simulations for the first time, provide a powerful means to analyse in detail the complex dynamics of tilted black hole-torus systems. We show how its use helps to gain insight in the overall dynamics of the system, discussing the origin of the observed black hole precession and the development of a global non-axisymmetric $m=1$ mode in the disc. Our three-dimensional simulations show the presence of quasi-periodic oscillations (QPOs) in the instantaneous accretion rate, with frequencies in a range compatible with those observed in low mass X-ray binaries with either a black hole or a neutron star component. The frequency ratio of the dominant low frequency peak and the first overtone is $o_1/f \sim 1.9$, a frequency ratio not attainable when modelling the QPOs as $p$-mode oscillations in axisymmetric tori.