Hydrodynamic Simulations of Oscillating Shock Waves in a Sub-Keplerian Accretion Flow Around Black Holes

TL;DR

This study uses numerical simulations to analyze oscillating shock waves in accretion flows around black holes, revealing complex behaviors and oscillation patterns that influence observable properties.

Contribution

The paper introduces detailed hydrodynamic simulations of shock oscillations in black hole accretion flows, highlighting the role of turbulence and shock dynamics.

Findings

Flow behaves as constant height pre-shock and vertical equilibrium post-shock.

Post-shock infall time exceeds free-fall time by several times.

Shock oscillations exhibit coupled harmonic behavior with distinct frequencies.

Abstract

We study the accretion processes on a black hole by numerical simulation. We use a grid based finite difference code for this purpose. We scan the parameter space spanned by the specific energy and the angular momentum and compare the time-dependent solutions with those obtained from theoretical considerations. We found several important results (a) The time dependent flow behaves close to a constant height model flow in the pre-shock region and a flow with vertical equilibrium in the post-shock region. (c) The infall time scale in the post-shock region is several times higher than the free-fall time scale. (b) There are two discontinuities in the flow, one being just outside of the inner sonic point. Turbulence plays a major role in determining the locations of these discontinuities. (d) The two discontinuities oscillate with two different frequencies and behave as a coupled harmonic oscillator. A Fourier analysis of the variation of the outer shock location indicates higher power at the lower frequency and lower power at the higher frequency. The opposite is true when the analysis of the inner shock is made. These behaviours will have implications in the spectral and timing properties of black hole candidates.