Stability of Accretion Discs around Magnetized Stars

Tessema, Solomon Belay

doi:10.4236/ijaa.2014.42026

Cited by 5 publications

(9 citation statements)

References 13 publications

(13 reference statements)

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“…Although the influence of radial viscosity is often neglected in the geometrically thin accretion discs (e.g., Shakura & Sunyaev 1976;Abramowicz et al 1984;Cao & Zhang 1994;Wu et al 1995 a, b, c;Chen & Taam 1995;Tessema 2014), this quantity plays an important role in the inner region of an accretion disc and in the advection-dominated discs (Wu 1997;Ding et al 2000;KK13;KK14). Radial component of the stress tensor cannot be ignored when the radial viscosity is significant.…”

Section: Radial Viscositymentioning

confidence: 99%

The local stability of the magnetized advection-dominated discs with the radial viscous force

Ghoreyshi

Shadmehri

2018

Monthly Notices of the Royal Astronomical Society

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We study local stability of the advection-dominated optically thick (slim) and optically thin discs with purely toroidal magnetic field and the radial viscous force using a linear perturbation analysis. Our dispersion relation indicates that the presence of magnetic fields and radial viscous force cannot give rise to any new mode of the instability. We find, however, that growth rate of the thermal mode in the slim discs and that of the acoustic modes in the slim and optically thin discs are dramatically affected by the radial viscous force. This force tends to strongly decrease the growth rate of the outward-propagating acoustic mode (O-mode) at the short-wavelength limit, but it causes a slim disc to become thermally more unstable. We find that growth rate of the thermal mode increases in the presence of radial viscous force. This enhancement is more significant when the viscosity parameter is large. We also show that growth rate of the O-mode reduces when radial viscous force is considered. The growth rates of the thermal and acoustic modes depend on the magnetic field. Although the instability of O-mode for a stronger magnetic field case has a higher growth rate, the thermal mode of the slim discs can be suppressed when the magnetic field is strong. The inertialacoustic instability of a magnetized disc may explain the quasi-periodic oscillations (QPOs) from the black holes.

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Section: Radial Viscositymentioning

confidence: 99%

The local stability of the magnetized advection-dominated discs with the radial viscous force

Ghoreyshi

Shadmehri

2018

Monthly Notices of the Royal Astronomical Society

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“…Stability has become an important in many area of astrophysical research. Many authors has been studied the stability in different models (for example, [7] [8]). Both authers didn't address stability and mass transfer in binary stellar evolution.…”

Section: Classified Mass Transferring Binaries On the Basis Of What Smentioning

confidence: 99%

Mass Transfer in Binary Stellar Evolution and Its Stability

Negu¹,

Tessema²

2015

IJAA

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The evolution of a binary star system by various analytical and numerical approximations of mass transfer rate normalized to the equilibrium rate and its stability conditions are investigated. We present results from investigations of mass transfer and stability in close binary star systems using the different orbital parameters. The stability and instability of mass transfer in binary star evolution depends on the exchange of material which the response of the binary to the initial Roche lobe overflow causes the donor to loose even more material. Our work is mainly focused on basic mathematical derivations, analytical and numerical solutions in order to explain the mass transfer system in different orbital parameters as well as the results are compared with previous studies in both cases. Mass transfer is usually stable, as long as the winds specific angular momentum does not exceed the angular momentum per reduced mass of the system. This holds for both dynamical and thermal time scales. Those systems which are not stable will usually transfer mass on the thermal time scale. The variation of Roche lobe radius with mass ratio in the binary, for various orbital parameters in the conservative and non-conservative mass transfer, as well as the evolution equations, orbital angular momentum of the binary system and the corresponding analytical and numerical solutions for different cases, under certain restrictive approximations is derived, simulated and discussed.

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“…Using MHD equations, Tessema and Torkelsson (2010) studied the structure of thin accretion discs around magnetized stars to explain the effect of magnetic field on the structure of star in the presence of viscosity. Tessema (2011) also explained the stability and instability of stars for time-dependent discs in the presence of viscosity starting from MHD equations. Mikhailovskii et al (2008) studied magnetic instabilities in collisionless astrophysical rotating plasma with anisotropic pressure by using the MHD-kinetic description of the perturbed plasma.…”

Section: Introductionmentioning

confidence: 99%

Gravitational instability on propagation of MHD waves in astrophysical plasma

Cherkos

Tessema

2013

J. Plasma Phys.

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We determine the general dispersion relation for the propagation of magnetohydrodynamic (MHD) waves in astrophysical plasma by considering the effect of gravitational instability and viscosity with anisotropic pressure tensor and heat-conducting plasma. Basic MHD equations have been derived and linearized by the method of perturbation to develop the general form of dispersion relation equation. Our result indicates that the transverse propagation of waves in such a plasma is affected by the inclusion of heat conduction. For wave propagation, parallel to the magnetic field direction, we find that the fairhose mode is unaffected, whereas the mode corresponding to the gravitational instability is modified in astrophysical plasma with anisotropic pressure tensor being stable in the presence of viscosity and strong magnetic field at considerable wavelength.

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Stability of Accretion Discs around Magnetized Stars

Cited by 5 publications

References 13 publications

The local stability of the magnetized advection-dominated discs with the radial viscous force

The local stability of the magnetized advection-dominated discs with the radial viscous force

Mass Transfer in Binary Stellar Evolution and Its Stability

Gravitational instability on propagation of MHD waves in astrophysical plasma

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