Properties of accretion shock waves in viscous flows with cooling effects

We study the properties of the shock waves for a viscous accretion flow having low angular momentum in presence of synchrotron cooling. We present all possible accretion solutions in terms of flow parameters. We identify the region of the parameter space for steady and oscillating shocks and show the effect of various energy dissipation processes on it. We discuss the role of the shock waves while explaining the observations from black hole candidates.Comment: 3 pages; 3 figures; prepared on the basis of the talk presented in the MG11 Meeting on General Relativity, Berlin, July 23-29, 200

Parameter space study of magnetohydrodynamic flows around magnetized compact objects

We solve the magnetohydrodynamic (MHD) equations governing axisymmetric flows around neutron stars and black holes and found all possible solution topologies for adiabatic accretion. We divide the parameter space spanned by the conserved energy and angular momentum of the flow in terms of the flow topologies. We also study the possibility of the formation of the MHD shock waves.Comment: 3 pages; 4 figures; prepared on the basis of the talk presented in the MG11 Meeting on General Relativity, Berlin, July 23-29, 200

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.Comment: 6 Pages, 4 figures, RECTO 2013 conference proceedings published in Astronomical Society of India Conference Serie

Turbulence and Magnetic Fields in the Large Scale Structure of the Universe

The nature and origin of turbulence and magnetic fields in the intergalactic space are important problems that are yet to be understood. We propose a scenario in which turbulent flow motions are induced via the cascade of the vorticity generated at cosmological shocks during the formation of the large scale structure. The turbulence in turn amplifies weak seed magnetic fields of any origin. Supercomputer simulations show that the turbulence is subsonic inside clusters/groups of galaxies, whereas it is transonic or mildly supersonic in filaments. Based on a turbulence dynamo model, we then estimate that the average magnetic field strength would be a few microgauss inside clusters/groups, approximately 0.1 microgauss around clusters/groups, and approximately 10 nanogauss in filaments. Our model presents a physical mechanism that transfers the gravitation energy to the turbulence and magnetic field energies in the large scale structure of the universe.Comment: Appeared in Science 320, 909 (16 May 2008). Pdf with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/rkcd.pd