Periodic massloss from viscous accretion flows around black holes

TL;DR

This study uses SPH simulations to show how viscosity-induced shock oscillations in accretion flows around black holes lead to periodic matter ejections and radiation modulations, resembling observed black hole variability.

Contribution

It demonstrates the role of viscosity in causing shock oscillations and periodic outflows in accretion flows, linking theoretical models to observed black hole phenomena.

Findings

Shock becomes time-dependent and oscillates with increased viscosity.

Periodic ejection of matter as outflows occurs due to shock oscillations.

Photon flux modulates quasi-periodically with fundamental frequencies of a few Hz.

Abstract

We investigate the behaviour of low angular momentum viscous accretion flows around black holes using Smooth Particle Hydrodynamics (SPH) method. Earlier, it has been observed that in a significant part of the energy and angular momentum parameter space, rotating transonic accretion flow undergoes shock transition before entering in to the black hole and a part of the post-shock matter is ejected as bipolar outflows, which are supposed to be the precursor of relativistic jets. In this work, we simulate accretion flows having injection parameters from the inviscid shock parameter space, and study the response of viscosity on them. With the increase of viscosity, shock becomes time dependent and starts to oscillate when the viscosity parameter crosses its critical value. As a result, the in falling matter inside the post-shock region exhibits quasi-periodic variations and causes periodic ejection of matter from the inner disc as outflows. In addition, the same hot and dense post-shock matter emits high energy radiation and the emanating photon flux also modulates quasi-periodically. Assuming a ten solar mass black hole, the corresponding power density spectrum peaks at the fundamental frequency of few Hz followed by multiple harmonics. This feature is very common in several outbursting black hole candidates. We discuss the implications of such periodic variations.