Breathing Oscillations in a Global Simulation of a Thin Accretion Disk

TL;DR

This paper presents a detailed simulation of a thin accretion disk around a black hole, revealing strong breathing oscillations and their harmonics, which are characterized through eigenfunction analysis.

Contribution

It introduces a comprehensive general relativistic hydrodynamical simulation of a thin accretion disk that captures and analyzes breathing oscillations and their harmonics.

Findings

Strong breathing oscillations observed in the simulation.

Harmonics of the breathing oscillation are clearly identified.

Eigenfunctions confirm the breathing nature of the oscillations.

Abstract

We study the oscillations of an axisymmetric, viscous, radiative, general relativistic hydrodynamical simulation of a geometrically thin disk around a non-rotating, $6.62\,M_\odot$ black hole. The numerical setup is initialized with a Novikov-Thorne, gas-pressure-dominated accretion disk, with an initial mass accretion rate of $\dot{m} = 0.01\,L_\mathrm{Edd}/c^2$ (where $L_\mathrm{Edd}$ is the Eddington luminosity and $c$ is the speed of light). Viscosity is treated with the $\alpha$-prescription. The simulation was evolved for about $1000$ Keplerian orbital periods at three Schwarzschild radii (ISCO radius). Power density spectra of the radial and vertical fluid velocity components, the total (gas $+$ radiation) midplane pressure, and the vertical component of radiative flux from the photosphere, all reveal strong power at the local breathing oscillation frequency. The first, second and third harmonics of the breathing oscillation are also clearly seen in the data. We quantify the properties of these oscillations by extracting eigenfunctions of the radial and vertical velocity components and total pressure. This confirms that these oscillations are associated with breathing motion.