Unification to the "Pseudo-General-Relativistic" analysis of accretion disks around rotating black holes and neutron stars

Abstract

I analyse the relativistic accretion phenomena around rotating black holes and neutron stars in pseudo-Newtonian approach and show both the kinds of disk can be treated in an unified manner. For this purpose, number of pseudo-Newtonian potentials are in literature, applicable to describe the relativistic properties of accretion disk. While, Kerr metric is used to describe the pseudo-Newtonian potential for accretion disk around black hole, the Hartle-Thorne metric is considered to describe disk around neutron star. Two other potentials were proposed to describe the temporal effects of the accretion disk. Using these potentials, I study the global parameter space of the accretion disk around black holes and neutron stars. I show that, for different angular momenta of the compact object, the valid disk parameter region dramatically changes and disk may become unstable in certain situations. To bring it in the stable situation, the angular momentum of the accreting matter has to be reduced/enhanced (for co/counter-rotating disk) by means of some physical process. I also study, how the fluid properties get changed with different rotations of the compact objects. Moreover, I show the effect of viscosity to the fluid properties of the disk. Thus, I find out the unified physical parameter regime, for which the stable accretion disk can be formed. Subsequently, a theoretical prediction of kHz QPO is given, for a fast rotating compact object as 4U 1636-53.