Browsing by Author "Mukhopadhyay, B."

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Description of pseduo-Newtonina potential for the relativistic accretion disk around kerr black holes
(2002-04-01) Mukhopadhyay, B.
We present a pseudo-Newtonian potential for accretion disk modeling around the rotating black holes. This potential can describe the general relativistic eﬀects on accretion disk. As the inclusion of rotation in a proper way is very important at an inner edge of disk the potential is derived from the Kerr metric. This potential can reproduce all the essential properties of general relativity within 10% error even for rapidly rotating black holes.
Disk-Outflow system around spinning black holes and explaining the observed FSRQ-BL Lac dichotomy
(2011-01-29) Mukhopadhyay, B.
Global solution of viscous accretion disk around rotating compact objects : A pseudo-general-relativistic study
(2011-07-05) Mukhopadhyay, B.; Ghosh, Shubhrangshu
We study the solution of viscous accretion disks around rotating com-pact/central object having hard surface i.e. neutron star, strange star and any other highly gravitating objects. We choose pseudo-Newtonian approach to describe the relativistic accretion disk. For this purpose, a new pseudo- Newtonian potential is established which is applicable to describe the rela- tivistic properties of star and its disk. As we know, the Hartle-Thorne met- ric can describe geometry of star as well as the space-time out-side of it, we use this metric to establish our potential. Our potential reproduces the marginally stable orbit exactly as that of general relativity. It also reproduces the marginally bound orbit and speciﬁc mechanical energy at the marginally stable orbit with at most 4% and 10% error respectively. Using this poten- tial we study the global parameter space of the accretion disk. Thus, we ﬁnd out the physical parameter regime, for which the stable accretion disk can be formed around gravitating object with hard surface. We also study, how the ﬂuid properties get changed with diﬀerent rotations of the central star. We show that with the change of rotation to the central object, the valid disk parameter region dramatically changes.We also show the eﬀect of viscosity to the ﬂuid properties of the disk. Subsequently, we give a theoretical prediction
Gravitationally induced neutrino asymmetry
(2011-07-05) Singh, Parampreet; Mukhopadhyay, B.
We study the propagation of Dirac neutrinos in gravitational backgrounds and show that the gravitational interaction can lead to neutrino asymmetry due to modi cations in dispersion relation. We give some examples of spacetime geometries where such asym- metry can arise. This asymmetry would have contributed to the relic neutrino asymmetry through the interaction of neutrinos with primordial black holes before neutrinos decou- pled. In the present epoch it may be generated in accretion around high temperature rotating black holes.
Origin and interpretation of kilohertz QPOs from strange stars in X-ray Binary system: Theoretical hydrodynamical description
(2011-07-05) Mukhopadhyay, B.; Ray, Subharthi; Dey, Jishnu; et al.
We model and interpret the Kilohertz QPOs from the hydrodynamical description of accretion disk around a rapidly rotating compact strange star. The higher QPO frequency is described by the viscous eﬀects of accretion disk leading to shocks, while the lower one is taken to be the Keplerian motion of the accreting matter. Comparing our results with the observations for two of the fastest rotating compact stellar candidates namely, 4U 1636−53 and KS 1731−260, we ﬁnd that they match to a very good approximation, thus interpreting them as strange stars.
Pseudo-Newtonian Potentials to Describe the Temporal Effects on Relativistic Accretion Disks around Rotating Black Holes and Neutron Stars
(2002-01-02) Mukhopadhyay, B.; Misra, Ranjeev
Two pseudo-Newtonian potentials, which approximate the angular and epicyclic frequencies of the relativistic accretion disk around rotating (and counter rotating) compact objects, are presented. One of them, the Logarithmically Modiﬁed Potential, is a better approximation for the frequencies while the other, the Second-order Expanded potential, also reproduces the speciﬁc energy for circular orbits in close agreement with the General Relativistic values. These potentials may be included in time dependent hydrodynamical simulations to study the temporal behavior of such accretion disks
Stability of accretion disk around rotating black holes: a pseudo-general-relativistic fluid dynamical study
(2012-03-13) Mukhopadhyay, B.
We discuss the solution of accretion disk when the black hole is chosen to be rotating. We study, how the ﬂuid properties get aﬀected for diﬀerent rotation parameters of the black hole. We know that no cosmic object is static in Universe. Here the eﬀect of the rotation of the black hole to the space-time is considered following an earlier work of the author, where the pseudo-Newtonian potential was prescribed for the Kerr geometry. We show that, with the inclusion of rotation of the black hole, the valid disk parameter region dramatically changes and disk becomes unstable. Also we discuss about the possibility of shock in accretion disk around rotating black holes. When the black hole is chosen to be rotating, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable. 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
Unification to the Pseudo-General-Relativistic Analysis of Accretion Disks around rotating Black Holes and Neutron Stars
(2011-07-05) Mukhopadhyay, B.
I analyse the relativistic accretion phenomena around rotating black holes and neutron stars and show both the kinds of disk can be treated in an uniﬁed manner. The corresponding accretion disks are described by pseudo-Newtonian approach. 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 as the metric can describe continuously the space-time, inside the star as well as out-side of it. Two other potentials were proposed to describe the temporal eﬀects of the accretion disk. All the potentials reproduce the marginally stable and bound orbits approximately or exactly as that of general relativity. These also reproduce the speciﬁc mechanical energy approximately. Using these potentials, I study the global parameter space of the accretion disk around black holes and neutron stars. I study, how the ﬂuid properties get aﬀected for diﬀerent angular momentum of the compact object. 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. Also I discuss about the possibility of shock in accretion disk around rotating black holes and neutron stars. When the angular momentum of compact object is chosen to be varied, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable. 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 black holes, neutron stars and other gravitating central stars. 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.