Formation of non-steady outflows and QPOs around black hole
  We study the time dependent properties of sub-Keplerian viscous accretion flow around the black holes. We find that rotating matter feels centrifugal barrier on the way towards the black holes and eventually, shock transition is triggered allowing a part of the post-shock matter to eject out as bipolar outflow. This outflowing matters are supposed to be the precursor of relativistic jets. As viscosity is increased, shock becomes unsteady and start to oscillate when viscosity reached its critical value. This causes the inner part of the disk unsteady resulting periodic ejection of matter from the post-shock region. Also, the same hot and dense post-shock matter emits high energy radiation which modulates quasi-periodically. The power density spectra confirms this features as most of the power is concentrated at a narrow frequency range --- a characteristics (i. e. Quasi-Periodic Oscillation) commonly seen in several outbursting black hole candidates. 
Santabrata Das, Indranil Chattopadhyay and Aunj Nandi
astro-ph.HE