66 research outputs found
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
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