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1.
Within the formalism of Tsallis nonextensive statistics designed to describe the behavior of anomalous systems, systems with a strong gravitational interaction between their individual parts and the fractal nature of phase space, we have obtained linearized equations for the oscillations of a rigidly rotating disk by taking into account dissipative effects and give a derivation of the dispersion equation in the WKB approximation. Based on the previously derived modified Navier—Stokes hydrodynamic equations (the so-called equations of q-hydrodynamics), we have analyzed the axisymmetric oscillations of an astrophysical, differentially rotating gas—dust cosmic object and obtained modified Jeans and Toomre gravitational instability criteria for disks with a fractal phase-space structure. 相似文献
2.
The gravitational instability of flow through porous medium for some hydrodynamical and hydromagnetical systems of astrophysical interest is investigated. The effects of rotation, magnetic field, viscosity and finite electrical conductivity are studied for the gravitational instability through porous medium. The effect of suspended particles on the instability is also considered. It is found that Jean's criterion remains unchanged in the presence of porosity, viscosity, finite conductivity, rotation, magnetic field and suspended particles in the medium. 相似文献
3.
In many magnetized, dilute astrophysical plasmas, thermal conduction occurs almost exclusively parallel to magnetic field
lines. In this case, the usual stability criterion for convective stability, the Schwarzschild criterion, which depends on
entropy gradients, is modified. In the magnetized long mean free path regime, instability occurs for small wavenumbers when
(∂ P/∂z) (∂ ln T/∂ z) > 0, which we refer to as the Balbus criterion. We refer to the convective-type instability that results
as the magnetothermal instability (MTI). We use the equations of MHD with anisotropic electron heat conduction to numerically
simulate the linear growth and nonlinear saturation of the MTI in plane-parallel atmospheres that are unstable according to
the Balbus criterion. The linear growth rates measured from the simulations are in excellent agreement with the weak field
dispersion relation. The addition of isotropic conduction, e.g. radiation, or strong magnetic fields can damp the growth of
the MTI and affect the nonlinear regime. The instability saturates when the atmosphere becomes isothermal as the source of
free energy is exhausted. By maintaining a fixed temperature difference between the top and bottom boundaries of the simulation
domain, sustained convective turbulence can be driven. MTI-stable layers introduced by isotropic conduction are used to prevent
the formation of unresolved, thermal boundary layers. We find that the largest component of the time-averaged heat flux is
due to advective motions as opposed to the actual thermal conduction itself. Finally, we explore the implications of this
instability for a variety of astrophysical systems, such as neutron stars, the hot intracluster medium of galaxy clusters,
and the structure of radiatively inefficient accretion flows.
J. M. Stone: Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544 相似文献
4.
The effect of a non-uniform magnetic field on the gravitational instability for a non-uniformly rotating, infinitely extending
axisymmetric cylinder in a homogeneous medium has been studied. The Bel and Schatzman criterion of gravitational instability for a non-uniformly rotating medium is modified under the effect of a non-uniform/uniform
magnetic field acting along the tangential and axial directions. As a consequence the stabilizing and destabilizing effect
of the non-uniform magnetic field is obtained, a new criterion for the magneto-gravitational instability is deduced in terms
of Alfven’s wave velocity; and it is also found that the Jeans criterion determines the gravitational instability in the absence of rotation and when the non-uniform/uniform magnetic field acts
along the axis of the cylinder. 相似文献
5.
Vladimír Majerník 《Astrophysics and Space Science》1982,84(1):191-204
The Maxwell-like gravitational field equations have been generalized and coupled through the gravitational four-potential on the electromagnetic Maxwell's equations. It is shown that this has several astrophysical consequences, of which the main are the following (i) the gravitational instability of a system of mass bodies manifesting itself by a Hubble-like motion on cosmological scales, (ii) the possible change of light intensity propagating through a large distance (and so a possible change of the real energy output of some very distant objects, e.g., quasars), (iii) non-stability of a planetary system on the cosmological time scales, due to the momentum increase of the moving bodies in a generalized gravitational field. 相似文献
6.
Collisionally-induced amplification of density fluctuations can also produce non-axisymmetric local condensations in particulate discs if the optical thickness is between definite values. Gravitational instability occurs above this interval. The theory of both phenomena is derived from collisional equations. The conventional criterion for gravitational instability in a gaseous medium cannot be used for particulate discs, in which the equilibrium depends on the collisional energy loss. These instabilities can produce an unbounded growth in density or a gravitational coagulation of particles, but the typical consequence is the formation of highly elongated clouds which are denser than the background matter and have a relatively long lifetime before decay. The third type of instability, the thermal one, appears at low values of velocity dispersion. It only affects the random motion of particles without producing condensations. 相似文献
7.
The effect of rotation on the self-gravitational instability of an infinite homogeneous magnetised gas-particle medium in the presence of suspended particles is investigated. The conductivity of the medium is assumed to be finite. The equations of the problem are linearized and the general dispersion relation is obtained. The rotation is assumed along two different directions separately and separate dispersion relation for each case is obtained. The dispersion relation for propagation parallel and perpendicular to the uniform magnetic field along with rotation is derived. It is found that in presence of suspended particles, magnetic field, finite conductivity, rotation and viscosity, Jeans's criterion determines the condition of gravitational instability of gas-particle medium. 相似文献
8.
The problem of self-gravitational instability of an infinite, homogeneous stratified gaseous medium with finite thermal conductivity and infinite electrical conductivity, in the presence of non-uniform rotation and magnetic field in the Chandrasekhar’s frame of reference, is studied. It is found that the magnetic field, whether uniform or non-uniform, has no effect on the Jeans’ criterion for gravitational instability and remains essentially unaffected. However, the thermal conductivity has the usual stabilizing effect on the criterion that the adiabatic sound velocity occurring in the Jeans criterion is replaced by the isothermal sound velocity. Thus, the present analysis extends the results of Chandrasekhar for the case of heat conducting medium and for non-uniform rotation and magnetic field. 相似文献
9.
The gravitational instability of an infinite homogeneous self-gravitating plasma through porous medium is considered to include, separately, the effects due to rotation and collisions between ionized and neutral components. The dispersion relations are obtained in both cases. It is found that the gravitational instability of a composite and rotating plasma in the presence of a variable horizontal magnetic field through porous medium is determined by the Jeans's criterion. 相似文献
10.
K. C. Sharma 《Astrophysics and Space Science》1982,85(1-2):263-269
The gravitational instability of an infinite homogeneous and infinitely conducting selfgravitating gas particle medium in the presence of suspended particles of a Hall plasma is considered. The particular cases of the effects of Hall currents and suspended particles on the waves propagated along and perpendicular to magnetic field have been discussed. Jeans's criterion determines the gravitational instability. 相似文献
11.
R. P. Prajapati R. K. Pensia S. Kaothekar R. K. Chhajlani 《Astrophysics and Space Science》2010,327(1):139-154
The effects of arbitrary radiative heat-loss functions and Hall current on the self-gravitational instability of a homogeneous,
viscous, rotating plasma has been investigated incorporating the effects of finite electrical resistivity, finite electron
inertia and thermal conductivity. A general dispersion relation is obtained using the normal mode analysis with the help of
relevant linearized perturbation equations of the problem, and a modified Jeans criterion of instability is obtained. The
conditions of modified Jeans instabilities and stabilities are discussed in the different cases of our interest. We find that
the presence of arbitrary radiative heat-loss functions and thermal conductivity modifies the fundamental Jeans criterion
of gravitational instability into a radiative instability criterion. The Hall parameter affects only the longitudinal mode
of propagation and it has no effect on the transverse mode of propagation. For longitudinal propagation, it is found that
the condition of radiative instability is independent of the magnetic field, Hall parameter, finite electron inertia, finite
electrical resistivity, viscosity and rotation; but for the transverse mode of propagation it depends on the finite electrical
resistivity, the strength of the magnetic field, and it is independent of rotation, electron inertia and viscosity. From the
curves we find that the presence of thermal conductivity, finite electrical resistivity and density-dependent heat-loss function
has a destabilizing influence, while viscosity and magnetic field have a stabilizing effect on the growth rate of an instability.
The effect of arbitrary heat-loss functions is also studied on the growth rate of a radiative instability. 相似文献
12.
The self-gravitating instability of an infinitely extending axisymmetric cylinder of viscoelastic medium permeated with non uniform magnetic field and rotation is studied for both the strongly coupled plasma (SCP) and weakly coupled plasma (WCP). The non uniform magnetic field and rotation are considered to act along the axial direction of the cylinder. The normal mode method of perturbations is applied to obtain the dispersion relation. The condition for the onset of gravitational instability has been derived from the dispersion relation under both strongly and weakly coupling limits. It is found that the Jeans criterion for gravitational collapse gets modified due to the presence of shear and bulk viscosities for the SCP, however, the magnetic field and rotation whether uniform or non uniform has no effect on the Jeans criterion of an infinitely extending axisymmetric cylinder of a self-gravitating viscoelastic medium. 相似文献
13.
The effect of rotation on the self-gravitational instability of an infinite homogeneous magnetized Hall plasma is considered with the inclusion of finite Larmor radius corrections and the effect of suspended particles. A general dispersion relation is obtained from the linearized set of equations. The particular cases of the effect of rotation along and perpendicular to the direction of the magnetic field are considered. The effects of Hall current, finite Larmor radius, and suspended particles on the waves propagated parallel and perpendicular to the uniform magnetic field are investigated along with the uniform rotation of the medium. It is found that in the presence of suspended particles, magnetic field, Hall current, rotation and finite Larmor radius, the Jeans criterion determines the condition of gravitational instability of a gas-particle medium. 相似文献
14.
R. C. Sharma 《Astrophysics and Space Science》1977,46(2):255-259
The gravitational instability of an infinite homogeneous and infinitely conducting self-gravitating gas-particle medium in the presence of a vertical magnetic field and suspended particles is considered. It is found that in the presence of suspended particles and magnetic field, Jeans' criterion determines the gravitational instability. 相似文献
15.
A. V. Kolesnichenko 《Solar System Research》2017,51(2):127-144
The long-time development of self-gravitating gaseous astrophysical systems (in particular, the evolution of the protoplanet accretion disk) is mainly determined by relatively fast processes of the collision relaxation of particles. However, slower dynamical processes related to force (Newton or Coulomb) interactions between particles should be included (as q-collisions) in the nonextensive kinetic theory as well. In the present paper, we propose a procedure to include the Newton self-gravity potential and the centrifugal potential in the near-equilibrium power-like q-distribution in the phase space, obtained (in the framework of nonextensive statistics) by means of the modified Boltzmann equation averaged with respect to an unnormalized distribution. We show that if the power distribution satisfies the stationary q-kinetic equation, then the said equation imposes clear restrictions on the character of the long-term force field and on the possible dependence of hydrodynamic parameters of the coordinates: it determines those parameters uniquely. We provide a thermodynamic stability criterion for the equilibrium of the nonextensive system. The results allow us to simulate the evolution of gaseous astrophysical systems (in particular, the gravitational stability of rotating protoplanet accretion disks) more adequately. 相似文献
16.
Solar System Research - In the framework of Tsallis statistics, we study the effect of medium nonextensivity on the Jeans gravitational instability criterion for a self-gravitating protoplanetary... 相似文献
17.
M. Anna Lakshmi S. Umapathy O. Prakash V. Vasanth 《Astrophysics and Space Science》2011,332(2):373-378
The paper investigates the effects of thermal conductivity and non-uniform magnetic field on the gravitational instability
of a non-uniformly rotating infinitely extending axisymmetric cylinder in a homogeneous heat conducting medium. The non-uniform
rotation and magnetic field are supposed to act along θ and z directions of the cylinder. It is found that the gravitational instability of this general problem is determined by the same
criterion as obtained by Dhiman and Dadwal (Astrophys. Space Sci. 325(2):195–200, 2010) for the self-gravitating isothermal medium in the presence of non-uniform rotation and magnetic field with the only difference
that adiabatic sound velocity is now replaced by the isothermal sound velocity. It is found that the thermal conductivity
has stabilizing effect on the onset of gravitational instability. Further, the stabilizing/destabilizing effect of the non-uniform
magnetic field on the gravitational instability of heat conducting medium has been discussed and is illustrated by considering
some special forms of the basic magnetic fields. 相似文献
18.
The gravitational instability of an infinite homogeneous self-gravitating and infinitely conducting gas-particle medium is considered in the presence of suspended particles and a variable horizontal magnetic field varying in vertical direction. It is found that the Jeans's criterion of instability remains unaffected even if the effects due to suspended particles and variable horizontal magnetic field are included. 相似文献
19.
Magnetically mediated disk outflows are a leading paradigm to explain winds and jets in a variety of astrophysical sources, but where do the fields come from? Since accretion of mean magnetic flux may be disfavored in a thin turbulent disk, and only fields generated with sufficiently large scale can escape before being shredded by turbulence, in situ field production is desirable. Nonlinear helical inverse dynamo theory can provide the desired fields for coronae and outflows. We discuss the implications for contemporary protostellar disks, where the (magneto-rotational instability (MRI)) can drive turbulence in the inner regions, and primordial protostellar disks, where gravitational instability drives the turbulence. We emphasize that helical dynamos are compatible with the magneto-rotational instability, and clarify the relationship between the two. 相似文献
20.
R. S. Sengar 《Astrophysics and Space Science》1983,89(2):285-291
A discussion of gravitational instability of a finitely conducting medium with streams of variable velocity distribution is made in the presence of a uniform magnetic field. It is found that the variable streaming motion shows a destabilizing effect and affects the instability criterion only in the case of general wave propagation. For purely parallel propagation to the direction of the magnetic field and the streaming motion, the criterion is independent of the variation in the streaming motion and further the Jeans's criterion is found to remain unaffected in this case. For purely transverse propagation, the criterion is independent of any streaming motion and the Jeans's criterion remains unaffected. The criterion is further independent of the magnetic field and the finite conductivity except in the case of transverse propagation where the magnetic field exhibits a stabilizing influence in case of an infinitely conducting medium. 相似文献