Global solution for a viscous accretion disc around a rotating compact object: pseudo-general-relativistic study

Mukhopadhyay, Banibrata; Ghosh, Shubhrangshu

doi:10.1046/j.1365-8711.2003.06537.x

Cited by 26 publications

(34 citation statements)

References 37 publications

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“…We assume β (and then γ) to be constant throughout the flow. Azimuthal momentum balance. where, following Mukhopadhyay & Ghosh (2003, hereafter MG03), the shearing stress can be expressed in terms of the pressure and density as Here, α is the dimensionless viscosity parameter and P eq and ρ eq are the pressure and density, respectively, at the equatorial plane. Note that we assume P eq ∼ P and ρ eq ∼ρ when obtaining the solutions. Energy production rate.…”

Section: Model Equations Describing the System And Solution Proceduresmentioning

confidence: 99%

Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

Rajesh

Mukhopadhyay

2010

Monthly Notices of the Royal Astronomical Society

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We investigate viscous two-temperature accretion disc flows around rotating black holes. We describe the global solution of accretion flows with a sub-Keplerian angular momentum profile, by solving the underlying conservation equations including explicit cooling processes self-consistently. Bremsstrahlung, synchrotron and inverse Comptonization of soft photons are considered as possible cooling mechanisms. We focus on the set of solutions for sub-Eddington, Eddington and super-Eddington mass accretion rates around Schwarzschild and Kerr black holes with a Kerr parameter of 0.998. It is found that the flow, during its infall from the Keplerian to sub-Keplerian transition region to the black hole event horizon, passes through various phases of advection: the general advective paradigm to the radiatively inefficient phase, and vice versa. Hence, the flow governs a much lower electron temperature ∼10 8 -10 9.5 K, in the range of accretion rate in Eddington units 0.01 Ṁ 100, compared to the hot protons of temperature ∼10 10.2 -10 11.8 K. Therefore, the solution may potentially explain the hard X-rays and γ -rays emitted from active galactic nuclei (AGNs) and X-ray binaries. We then compare the solutions for two different regimes of viscosity. We conclude that a weakly viscous flow is expected to be cooling dominated, particularly at the inner region of the disc, compared to its highly viscous counterpart, which is radiatively inefficient. With all the solutions in hand, we finally reproduce the observed luminosities of the underfed AGNs and quasars (e.g. Sgr A * ) to ultraluminous X-ray sources (e.g. SS433), at different combinations of input parameters, such as the mass accretion rate and the ratio of specific heats. The set of solutions also predicts appropriately the luminosity observed in highly luminous AGNs and ultraluminous quasars (e.g. PKS 0743-67).

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Section: Model Equations Describing the System And Solution Proceduresmentioning

confidence: 99%

Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

Rajesh

Mukhopadhyay

2010

Monthly Notices of the Royal Astronomical Society

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“…Ref. [76] shows that sub-Keplerian motion in the inner part of the accretion disk (r < ∼ 20 r g ) might cause a postshock region with hard X-ray emission. Hard X-ray emission also might come from the converging bulk motion of the accreting matter.…”

Section: A the Dependence Of The Amplitude On The Energymentioning

confidence: 99%

Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasiperiodic oscillations

Germanà

Casana

2015

Phys. Rev. D

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The twin-peak high-frequency quasi-periodic oscillations (HF QPOs), observed in the power spectra of low-mass X-ray binaries, might carry relevant clues about the physics laws reigning close to a compact object. Their frequencies are typical of the orbital motion time-scales a few gravitational radii away from the compact object. The aim of the manuscript is to propose an intuitive model explaining that the energy carried by the lower HF QPO can be related to differences of potential energy released by clumps of plasma spiraling in a curved space-time. Our model provides estimates on both the size of clumps of matter that can survive to the strong tidal force and energy loaded by tides on the clump. We have also obtained some constraints on the mechanical properties of the plasma orbiting into the accretion disk. We note that the systematic behavior of the emitted energy as function of the central frequency of the lower HF QPO, observed in several sources with a neutron star, might give clues related to an innermost stable bound orbit predicted by the General Relativity theory in strong field regime. PACS numbers: 95.30.Sf, 97.80.Jp, 97.10.Gz, 91.60.Ba

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“…In order to understand the underlying physics, let us consider the equations describing optically thin, viscous, magnetized, advective accretion disk [24]. We describe the model in the pseudo-Newtonian framework with the Paczyński-Wiita potential [25,26].…”

Section: Advective Accretion Flows Around Black Holesmentioning

confidence: 99%

Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?

Mukhopadhyay

2013

Physics Letters B

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String theory and gauge/gravity duality suggest the lower bound of shear viscosity (η) to entropy density (s) for any matter to be ∼ µ /4πk B , when and k B are reduced Planck and Boltzmann constants respectively and µ ≤ 1. Motivated by this, we explore η/s in black hole accretion flows, in order to understand if such exotic flows could be a natural site for the lowest η/s. Accretion flow plays an important role in black hole physics in identifying the existence of the underlying black hole. This is a rotating shear flow with insignificant molecular viscosity, which could however have a significant turbulent viscosity, generating transport, heat and hence entropy in the flow. However, in presence of strong magnetic field, magnetic stresses can help in transporting matter independent of viscosity, via celebrated Blandford-Payne mechanism. In such cases, energy and then entropy produces via Ohmic dissipation.In addition, certain optically thin, hot, accretion flows, of temperature > ∼ 10 9 K, may be favourable for nuclear burning which could generate/absorb huge energy, much higher than that in a star. We find that η/s in accretion flows appears to be close to the lower bound suggested by theory, if they are embedded by strong magnetic field or producing nuclear energy, when the source of energy is not viscous effects.A lower bound on η/s also leads to an upper bound on the Reynolds number of the flow.

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Global solution for a viscous accretion disc around a rotating compact object: pseudo-general-relativistic study

Cited by 26 publications

References 37 publications

Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasiperiodic oscillations

Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?

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