共查询到20条相似文献，搜索用时 656 毫秒
1.
The gravitational instability of an infinite homogeneous finitely conducting viscid fluid through porous medium is studied in the presence of a uniform vertical magnetic field and finite ion Larmor radius (FLR) effects. The medium is considered uniformly rotating along and perpendicular to the direction of the prevalent magnetic field. A general dispersion relation is obtained from the relevant linearized perturbation equations of the problem. Furthermore, the wave propagation along and perpendicular to the direction of existing magnetic field has been discussed for each direction of the rotation. It is found that the simultaneous presence of viscosity finite conductivity, rotation, medium porosity, and FLR corrections does not essentially change the Jeans's instability condition. The stabilizing influence of FLR in the case of transverse propagation is reasserted for a non-rotating and inviscid porous medium. It is shown that the finite conductivity has destabilizing influence on the transverse wave propagation whereas for longitudinal propagation finite conductivity does not affect the Jean's criterion. 相似文献
2.
K. Murawski 《Solar physics》1992,139(2):279-297
The nonlinear propagation of the Alfvén and magnetosonic waves in the solar corona is investigated in terms of model equations. Due to viscous effects taken into account the propagation of the fast wave itself is governed by Burgers type equations possessing both expansion and compression shock solutions. Numerical simulations show that both parallely and perpendicularly propagating fast waves can steepen into shocks if their amplitudes are in excess of some sizeable fraction of the Alfvén velocity. However, if the magnetic field changes linearly in the perpendicular direction, then formation of perpendicular shocks can be hindered. The Alfvén waves exhibit a tendency to drive both the slow and fast magnetosonic waves whose propagation is described by linearized Boussinesq type equations with ponderomotive terms due to the Alfvén wave. The limits of the slow and fast waves are investigated. 相似文献
3.
M. S. Ruderman 《Solar physics》1991,131(1):11-24
Surface magnetohydrodynamic wave propagation on a magnetic interface in a cold plasma is studied. The anisotropic ion viscosity is taken into account. Only long waves damping weakly in a wave period are considered. The dispersion equation is obtained. This equation is shown always to have exactly one root if there is no viscosity. The dependences of phase velocity, penetration depth and damping decrement of waves on the parameters of undisturbed plasma and wave propagation direction are investigated. The resulting application for describing of surface wave damping in the solar corona is discussed. 相似文献
4.
R. M. L. Baker 《Astronomische Nachrichten》2006,327(7):710-713
A novel formulation of the quadrupole equation for potential stellar gravitational‐wave power estimation is derived. The derivation commences with the classical Einstein quadrupole formalism and then utilizes Newton's second law to establish a simplified formulation involving the radius of gyration of a mass or system of masses involving a pair of massive stars either on orbit about one another, or otherwise separated, or a star with a dumbbell‐like or aspherical mass distribution and an impulsive force acting on the mass or masses in order to estimate the power of a gravitational wave that is generated. A numerical example, based upon the well‐known gravitational‐wave power observed to be generated by PSR 1913+16, is utilized to test the formulation. Potential applications to stellar jets, including stellar‐black‐hole produced jets, are cited as examples of the potential applications of the novel quadrupole formulation. It is suggested that the gravitational waves, generated by the applications suggested, might be detected by the proposed space‐based Laser Interferometer Space Antenna or LISA. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Hafiza Rizwana Kausar 《Astrophysics and Space Science》2018,363(11):238
In this paper, we formulate the gravitational wave equations in the hybrid metric-Palatini gravity and solve these equations to find the polarization states. This newly proposed theory is very successful in explaining the observed phenomenology based on the hybrid combination of Einstein Hilbert action and Palatini formalism of \(f(R)\) gravity. We compare the obtained results of gravitational polarized modes with the existing results in the original approaches of the hybrid combination. The difference in the results is due to the coupling of the Ricci scalar with the trace of the energy momentum tensor. 相似文献
6.
David F. Roscoe 《Astrophysics and Space Science》1995,227(1-2):119-132
It is shown that global four-momentum conservation provides all the necessary structure toderive a metric gravity theory which conforms to the requirements of the Strong Equivalence Principle (Will, 1981), and which satisfies all empirical tests up to, and including, those derived from the binary pulsar measurements. Significant consequences arising from this theory are: concepts of curved spacetimes become strictly superfluous to the function of describing gravitational physics; gravitational processes become direct particle/particle interactions; these interactions are arbitrated by wave processes of a kind familiar in electromagnetism; gravitational waves carry energy-momentum in the direction of their propogation vector; the essential singularities at gravitational origins, which are features of both Newtonian gravitation and General Relativity, do not exist. 相似文献
7.
It is generally believed that the heating of the solar corona is caused by waves originating in the photosphere and propagating into the corona where their energy is dissipated. The medium through which these waves propagate is in general permeated by magnetic fields complicating the behaviour of this propagation considerably. We have therefore analysed the wave motions in a plasma permeated by constant magnetic and gravitational fields. In general, three waves modes were found, which we called the + mode, –mode, and the Alfvén mode. Each mode was found to be strongly coupled to each of the three kinds of motion; acoustic, gravity, and hydromagnetic. However, the Alfvén mode was found to be separable from the dispersion relation, and therefore independent of compressibility and gravity. The local dispersion relation is derived and expressed in nondimensional form independent of the constants that describe a particular atmosphere. From the dispersion relation one can show that rising waves propagate either with a constant or a growing wave amplitude depending on the magnitudes and directions of the gravitational field, magnetic field, and the wave vector. The variation of the density with height is taken into account by a generalized W.K.B. method. Equations are found which give the height at which wave reflection occurs, giving the upper bound for possible wave propagation.Work supported by the National Aeronautics and Space Administration under Research Grant NGR-29-001-016.On leave of absence from the Desert Research Institute and Department of Physics, University of Nevada, Reno, Nevada, U.S.A. 相似文献
8.
Manh Dung Duong 《Planetary and Space Science》1976,24(10):907-914
This paper derives the basic propagation characteristics of hydromagnetic waves in various layers of the ionosphere. It is shown that propagation in the upper ionosphere and the F2 layer is largely isotropic. In the lower region of the ionosphere there are two possible modes of propagation, both being anisotropic. Propagation characteristics of waves in this lower region, however, are relatively independent of the direction of horizontal propagation. Calculations of intrinsic wave attenuation show that ducted propagation of Pc 1 signals over appreciable horizontal distances may only take place in the upper layers of the ionosphere. 相似文献
9.
Yu. V. Baryshev 《Astrophysics》1997,40(3):244-251
An equation is obtained for the cross section of a metal Weber cylinder for scalar gravitational waves, which are possible
within the framework of the field theory of gravitation. It is shown that the signals detected by the Amaldi and Weber antennas
during the explosion of supernova SN 1987A can be interpreted as the result of the action of scalar gravitational waves on
solid-state detectors. The required energy of the gravitational waves is about 1 M⊙c2. Together with the observed excess (about 1 %) of gravitational radiation from the binary system containing the pulsar PSR
1913+16, the signals from SN 1987A are the second piece of observational evidence for the actual existence of scalar gravitational
waves. The present-day, third-generation, solid-state antennas are capable of detecting scalar waves from events like SN 1987A
at a distance up to 5 Mpc. The expected level of the signal from SN 19931 is about 7 mK. An experimental test of the longitudinal
nature of scalar waves is possible using interferometric antennas based on free masses.
Translated from Astrofizika, Vol. 40, No. 3, pp. 377–389, August, 1997. 相似文献
10.
In this paper we have discussed two models of domain walls within the framework of Lyra geometry. An exact solution is obtained
for a thick non static domain wall. The space time is non singular both in its spatial and temporal behavior and the gravitational
field experienced by a test particle is attractive. It is found that these exists no particle horizon in our case. Also we
have presented a spherical domain wall with nonvanishing stress components in the direction perpendicular to the plane of
the wall. The gravitational field of the domain wall is shown to be attractive in nature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The gravitational stability of magnetized self-gravitating two-component plasma of finite conductivity flowing through porous medium is studied. Effect of magnetic field, porosity, viscosity, finite conductivity, and neutral gas friction is considered on the stability of the system. Dispersion relations are derived from linearized equations using normal mode analysis. Longitudinal and transverse wave propagations are discussed. On the basis of Hurwitz criterion, the stability of the system is discussed. It is found that Jeans's criterion determines the stability of the system. Jeans's expression depends on the sonic speeds in both the components. For transverse wave propagation in perfectly conducting plasma. Jeans's expression is modified due to magnetic field and porosity but in case of finitely conducting plasma the Jeans's expression remains unaltered. Collisional frequency, viscosity, permeability of the porous medium have damping effect. 相似文献
12.
J. J. Podesta 《Solar physics》2005,232(1-2):1-23
The solar convection zone is modeled as a horizontally stratified atmosphere with a constant gravitational field and an adiabatic
temperature gradient (a neutrally stratified polytrope). At equilibrium, the gas pressure and density decreases to zero at
the solar surface so that the solar surface is treated as a free surface which is bounded by vacuum. The evolution of small
amplitude perturbations about the equilibrium state is described by the linearized Euler equations for an inviscid compressible
fluid with an adiabatic equation of state. A sunquake is initiated at time zero by means of an initial perturbation with a
Gaussian velocity profile and the exact solution of the initial value problem is obtained in terms of a Fourier integral.
Comparisons between theory and observations indicate that this highly simplified model is able to predict the propagation
of sunquake waves across the solar surface with an error of approximately 10% or 20%. 相似文献
13.
The aim of this paper has been to study here specific forms of instabilities in circumstellar and circumplanetary dust ringlets in Keplerian rotation around a central gravitating mass without taking shear flow effects into consideration. Due to the presence of a central mass in the disk, an additional force term appears in the linearized equation of motion. Here we investigate the importance of such a term with respect to the onset of gravitational instabilities in both tangential and radial direction of ring-like substructures in the disk. In addition, we compare the instability tendencies of self-gravitating disks with those of fluid layers where perturbation effects are simply controlled by surface tension. In both cases, the material of the layer is treated as an incompressible inviscid fluid. This assumption, however, as shown from our study of the polytropy of dust gases, was proven to be correct for perturbation wavelengths comparable or larger than the thickness of the layer. From our general dispersion relations for symmetric and anti-symmetric perturbation modes, we can retain for the radial wave propagation the results of Lin and Shu, and Goldreich and Ward in the asymptotic case of an infinitely thin layer without shear flow. However, for the tangential waves we find a different stability criterion showing that the onset of the instability depends on the propagation direction. In the finite layer case, we derive much more general relations showing different instability ranges for bending wave modes and self-excited density wave modes pointing to local and global instability forms in ringlets. 相似文献
14.
The wave propagation in a finitely conducting, self-gravitating, non-relativistic hydromagnetic medium with temperature gradient and a heat-energy transport into it has been considered. Firstly, a General Dispersion Relation (G.D.R.) has been derived. The interest has been kept limited for the study of one dimensional wave propagation in a typical medium where magnetic field and it's gradient, density gradient, temperature gradient are all along the direction of wave propagation. The D.R. of such a medium follows from G.D.R. In particular, the effect of temperature gradient on the wave propagation has been studied. Analytical expressions for the wave parameters have been derived under different conditions. It has been found that the longitudinal waves could be sufficiently energetic for being unstable by the temperature gradient. Further, the modified Jeans' criterion (depending on temperature gradient), a criterion important for stability, has also been obtained.On assuming the gas medium in the central region ( 10 pc) of our Galaxy to behave like hydromagnetic fluid, and the direction of wave propagation (z-direction) as the direction perpendicular to the Galactic plane, few numerical estimations for the wave parameters (like wave lengths, phase velocity, etc.) have been made (as application of the above theoretical discussions). It has been found that the phase velocity of longitudinal waves at 1 pc level is at least 170 kms–1 while at the 10 pc level the longitudinal waves of length less than a parsec may propagate smoothly through the medium. It has been suggested that (i) in the central region ( 10 pc) of our Galaxy the temperature gradient could be one of the major causes of the mass-outflow along the direction perpendicular to the Galactic plane (ii) outside the central region ( 10 pc) of our Galaxy, there may be long term consequences of such mass-outflow like Halo formation. 相似文献
15.
Richard L. Harkness Jr. 《Solar physics》1969,10(1):154-167
A linearized magnetohydrodynamic formalism is used to examine the propagation in two dimensions of transverse waves in a plasma in which is embedded a curl-free magnetic field. Only waves of frequency less than the ion cyclotron frequency are considered. The behavior of a wave packet near the magnetic neutral point is deduced from the general solution to the problem, which is found in terms of Bessel functions whose order is frequency dependent. It is shown that a disturbance propagates through the medium with a group velocity that decreases from the speed of light at large distances from the neutral point to zero at the neutral point, and that the amplitudes of the velocities associated with the disturbance diverge there. It is suggested that the stagnation of waves near the origin and the deformation of the magnetic field resulting from the large plasma-flow velocities may provide a clue to the formation of the magnetic neutral sheet required by several flare theories and a theory of the acceleration of cosmic rays. 相似文献
16.
M. Kutschera 《Monthly notices of the Royal Astronomical Society》2003,345(1):L1-L5
Einstein's general relativity predicts that pressure, in general stresses, plays a similar role to energy density, ε=ρ c 2 (with ρ being the corresponding mass density), in generating gravity. The source of gravitational field, the active gravitational mass density, sometimes referred to as Whittaker's mass density, is ρgrav =ρ+ 3 p / c 2 , where p is pressure in the case of an ideal fluid. Whittaker's mass is not conserved, hence its changes can propagate as monopole gravitational waves. Such waves can be generated only by astrophysical sources with varying gravitational mass. Here we show that relativistic fireballs, considered in modelling gamma-ray burst phenomena, are likely to radiate monopole gravitational waves from high-pressure plasma with varying Whittaker's mass. Also, ejection of a significant amount of initial mass-energy of the progenitor contributes to the monopole gravitational radiation. We identify monopole waves with h 11 + h 22 waves of Eddington's classification which propagate (in the z -direction) together with the energy carried by massless fields. We show that the monopole waves satisfy Einstein's equations, with a common stress-energy tensor for massless fields. The polarization mode of monopole waves is Φ22 , i.e. these are perpendicular waves which induce changes of the radius of a circle of test particles only (breathing mode). The astrophysical importance of monopole gravitational waves is discussed. 相似文献
17.
It is suggested that longitudinal compression waves are propagating parallel to the solar surface from the umbra towards the photosphere. It is shown that the line-absorption coefficient is asymmetrical, when integrated over a wavelength of the compression wave. The effect of the waves on the line profile is discussed, and it is shown that asymmetrical line profiles of the type observed in sunspot penumbrae will be produced.With the Evershed effect interpreted as an acoustical wave phenomenon the propagation (of the waves) may also be perpendicular to the magnetic lines of force, whereas material motion is likely to be restricted to the direction along the lines of force. 相似文献
18.
Frank Verheest Peter Meuris R.L. Mace M.A. Hellberg 《Astrophysics and Space Science》1997,254(2):253-267
Perpendicularly propagating electromagnetic waves in magnetized, multispecies, self-gravitating dusty plasmas are investigated
in terms of their wave dispersion properties as well as with respect to their susceptibility to gravitational collapse. In
particular, waves on the ordinary as well as extraordinary mode branches are considered. Within the one-dimensional propagation
model employed, all modes except the ordinary mode produce density perturbations that can be unstable to gravitational collapse.
The wavelengths that are unstable are comparable to the well-known Jeans length for a neutral gas/dust, but there are interesting
modifications due to the presence of a magnetic field and charged particles. Furthermore, the effects of the gravitational
coupling of a multicomponent plasma to a neutral dust are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
《New Astronomy》2017
This paper attempts to formulate a way for calculating the intensity of gravitational wave from two point masses in Keplerian circular and elliptic orbits. The intensity is calculated with the assumption that the orbital plane of the binary undergoes small oscillation about the equilibrium x-y plane. This problem is simplification of a physically possible orbit where one of the point masses is spinning whereby the spin-orbit force drives the orbital plane to wobble in a complicated manner. It is shown that the total energy of gravitational wave emitted by the binary in this case is dominated by the parameters which take into account the oscillation of the plane. The results presented are in fact a generalization of the classic results of Landau and Lifshitz. 相似文献
20.
The one dimensional propagation of simple waves in the system of electron-positron and photon gas at relativistic temperatures
is considered. The presence of the transverse (across the wave propagation direction) velocity will change the dependencies
of the phase velocity and magnetosound velocity upon temperature essentially. It is shown that at the presence of transverse
velocity, the decrease of these characteristic velocities of simple wave takes place, while the time of shock wave formation
becomes shorter.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献