Gravity from refraction of CMB photons using the optical-mechanical analogy in general relativity

Relativistic light bending and gravitational lensing have traditionally been viewed purely as effects of spacetime curvature. Yet for many years they have also been treated as a quasi-refraction of light in a special optical medium, wherein the refractive index is considered proportional to the gravitational potential. We now propose that this ‘optical-mechanical analogy’ in general relativity can also account for gravity. Using classical optics we show that a photon moving through the refractive medium about a mass transfers momentum first to the medium and then to the mass itself. Due to transfer of momentum primarily from ultra-remote CMB photons, masses are then subject to a cosmic pressure on all sides. Where two masses occur, mutual screening by their respective envelopes of refractive medium is shown to result in an attractive force of the Le Sage or ‘pushing gravity’ type. We suggest that the gravito-optical medium is comprised of gravitons, which may be modeled as a quasi-Einstein-Bose conjugate interconnecting all the masses of the visible universe.     

Magneto-gravitational instability of a fluid through porous medium including finite ion Larmor radius

The magneto-gravitational instability of an infinite, homogenous, and infinitely conducting plasma flowing through a porous medium is studied. The finite ion Larmor radius (FLR) effects and viscosity are also incorporated in the analysis. The prevalent magnetic field is assumed to be uniform and acting in the vertical direction. A general dispersion relation has been obtained from the relevant linearized perturbation equations of the problem. The wave propagation parallel and perpendicular to the direction of the magnetic field have been discussed. It is found that the condition of the instability is determined by the Jeans criterion for a self-gravitating, infinitely conducting, magnetized fluid through a porous medium. Furthermore, for transverse perturbation FLR is found to have stabilizing influence when the medium is considered inviscid.     

Gravitational instability of a thermally-conducting plasma flowing through a porous medium in the presence of suspended particles

Magnetogravitational instability of a thermally-conducting, rotating plasma flowing through a porous medium with finite conductivity and finite Larmor radius in the presence of suspended particles has been investigated. The wave propagation has been considered for both parallel and perpendicular axes of rotation. Magnetic field is being taken in the vertical direction. A general dispersion relation has been derived through relevant linearized perturbation equations. It has been observed that the condition of instability is determined by the Jeans's criterion in its modifed form. Thermal conductivity replaces the adiabatic velocity of sound by the isothermal one. Rotation decreases the Larmor radius. Porosity decreases the Alfvén velocity. In case of a viscous medium the effects of FLR, rotation, and suspended particles are not observed in the Jeans's condition, for transverse propagation for rotational axis parallel to the magnetic field. The effects of rotation and FLR are decreased by the porosity and the suspended particles. Finite conductivity removes the Alfvén velocity from Jeans's condition.     

Critical properties of spherically symmetric accretion in a fractal medium

Spherically symmetric transonic accretion of a fractal medium has been studied in both the stationary and the dynamic regimes. The stationary transonic solution is greatly sensitive to infinitesimal deviations in the outer boundary condition, but the flow becomes transonic and stable when its evolution is followed through time. The evolution towards transonicity is more pronounced for a fractal medium than it is for a continuum, and in the former case the static sonic condition is met on relatively larger length scales. The dynamic approach also shows that there is a remarkable closeness between an equation  of motion for a perturbation in the flow, and the metric of an analogue acoustic black hole. The stationary inflow solutions of a fractal medium are as much stable under the influence of linearized perturbations as they are for the fluid continuum.     

Solar cycle dependence of periodic variations in geomagnetic Kp-index

The geomagnetic K_p-index data for the 1932–1969 period have been investigated by means of a modified power spectrum technique on the basis of overlapping 2-yr intervals. The observed 27-, and 13.5-day periodicities show an obvious solar cycle dependence through the whole period concerned. Also, periodicities in the range of 9?4 days have been observed through years of minimum and decreasing phases of solar activity. The periodicities observed are found to be related to the existence of variations in the interplanetary medium structure which modulates the geomagnetic activity.     

A more exact expression for the gravitational deflection of light,derived using material medium approach

The deflection of a ray of light passing close to a gravitational mass is generally calculated from the null geodesic which the light ray (photon) follows. However, there is an alternate approach, where the effect of gravitation on the ray of light is estimated by considering the ray to be passing through a material medium. Calculations have been done in this paper, following the latter approach, to estimate the amount of deflection due to a static non-rotating mass. The refractive index of such a material medium, has been calculated in a more rigorous manner in the present work, and the final expression for the amount of deflection calculated here is claimed to be more exact than all other expressions derived so far, using material medium approach. Based on this expression, the amount of deflection for a sun grazing ray has also been calculated. The exact amount of deflection can be performed in a number of ways, without the material medium approach. However, the method presented here using the material medium approach and without any weak field approximation is believed to be original.     

The cosmic microwave background radiation in a non-expanding universe

During the nineteenth century, it was common for physicists to believe in the existence of a material vacuum composed of an incompressible fluid that fills the whole universe. This fluid was called the aether. Its original purpose was to provide an elastic tenuous medium for light propagation through space. Although it is well understood today that no such medium is needed for light propagation, the existence of a cosmic aether medium in space is still possible and its physical properties can be understood on models of cosmology that have nothing to do with Big-Bang cosmology. It is possible that electromagnetic radiation emitted by the cosmic aether medium has already been detected. The low-frequency electromagnetic radiation emitted by the aether is called the cosmic microwave background radiation. The present study outlines a model for an aether medium that explains the genesis of the microwave background radiation in a closed static (nonexpanding) universe. It is shown that the spectrum of the microwave background radiation is a perfect blackbody with a temperature T _rad=2.77 K in harmony with the perfect cosmological principle. It is further shown that the aether medium is opaque at radio and microwave frequencies. This particular feature of the model does not contradict any observations regarding the existence of distant radio galaxies and quasars.     

Analytical Approach to Calculate Quasi-thermal Noise Spectrum in Irregular Plasma

Basic properties of quasi-thermal noise spectrum in irregular plasma have been investigated using an analytical point of view. A simple formula for the plasma frequency splitting effect has been obtained for ionospheric conditions. A passive electric antenna, immersed in a stable plasma, detects the fluctuations of the electric potential due to thermal motion of the ambient particles. Properties of this quasi-thermal noise spectrum in homogeneous plasma are relatively well known and are effectively used for diagnostics of space plasma (Aksenov et al., 1978; Trakhtengerts and Chugunov, 1978; Kellog, 1981; Meyer-Vernet and Perche, 1989). Especially, in the Earth's ionosphere or solar wind plasma, random irregularities of electron density are always present. These irregularities may substantially change properties of these media through electromagnetic radiation and may also modify quasi-thermal noise spectrum, which depends on the effective dielectric permittivity tensor. This tensor is defined as the dielectric permittivity tensor of some imaginary `effective' regular medium in which the field of point source is the same as the mean field in the medium with random irregularities (Ryzhov, Tamoikin and Tatarskii, 1965; Ryzhov 1968). Since the correlation function of electric field fluctuations in random medium may be expressed through the effective dielectric constant tensor (Ryzhov, 1968), it may be used for direct calculation of quasi-thermal noise spectrum. In Zabotin et al. (2000), the Born approximation was used to calculate numerically the effective dielectric permittivity tensor and the modified noise spectrum while we analytically estimate herein the modified noise spectrum. This revised version was published online in July 2006 with corrections to the Cover Date.     

An explosion model in magne to gasdynamics

By taking into account the interaction with magnetic field, in an axially symmetric inhomogeneous medium and assuming Gaussian density profile in radial direction instead of the cusped exponential law, a point explosion has been investigated by generalising the method suggested by Laumbach and Probstein (1969). The shock envelope becomes increasingly elongated along the axis of rotation, until it finally breaks through into the intergalactic space before it can spread considerably in equatorial directions as in ordinary gasdynamics. A comparison has been made between our results and those obtained in ordinary gasdynamics.Explosion models of double radio sources and related objects are suggested.     

The rayleigh-taylor instability of a stratified rotating fluid through a porous medium in a two-dimensional magnetic field

The effect of finite conductivity on the Rayleigh-Taylor instability of an incompressible, viscous rotating fluid through a porous medium has been studied in the presence of a two-dimensional horizontal magnetic field. It has been shown that the solution is characterized by a variational principle. By making use of the existence of the variational principle, proper solutions have been obtained for a semi-infinite fluid in which density has a one-dimensional (exponential) vertical stratification. The dispersion relation has been derived and solved numerically. It is found that finite resistivity and porosity have a destabilizing effect on the Rayleigh-Taylor instability while rotation has a stabilizing effect.     

Propagation of solitary waves in non uniform dusty plasmas

Interaction of dust acoustic solitary waves in plasmas consisting of medium disorders is investigated. Disorders and inhomogeneities of the medium are added to the equation of motion as perturbative terms through the medium parameters. The effects of these perturbations on the behaviour of solitary waves are studied with numerical simulations and the results are compared with theoretical predictions in a uniform media.     

Effect of temperature gradient on the wave propagation in a self-gravitating medium and its role in the central region of our Galaxy

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.     

Gravitational instability of a composite and rotating plasma in the presence of a variable magnetic field through a porous medium

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.     

Effect of thermal conductivity on the gravitational instability of a magnetized rotating plasma through a porous medium in the presence of suspended particles

The self-gravitational instability of an ionized, thermally-conducting, magnetized, rotating plasma flow through a porous medium has been studied in the presence of suspended particles. The ionized gas-particle medium has been considered rotating along and perpendicular to the vertical magnetic field. Propagation of the plasma waves has been studied for the longitudinal and the transverse modes for both the cases of rotation. A general dispersion relation has been derived with the help of relevant perturbation equations, using the method of normal mode analysis. The Jeans criterion determines the condition of gravitational instability in all the cases with some modifications introduced by the various parameters considered. Thermal conductivity replaces the adiabatic sonic speed by the isothermal one. Considering the longitudinal mode of propagation with perpendicular rotational axis, for an inviscid plasma with adiabatic behaviour the effect of both, the rotation and the suspended particles has been removed by the magnetic field. For the transverse mode of propagation with the axis of rotation parallel to the magnetic field, the viscosity removes the effect of both, the rotation and the suspended particles. Porosity reduces the effect of both, the rotation and the magnetic field, whereas the concentration of the suspended particles reduces the rotational effect.     

Origin of oort cloud comets in the interstellar space

Comets must form a major part of the interstellar medium. The solar system provides a flux of comets into the interstellar space and there is no reason to suspect that many other stars and their surrounding cometary systems would not make a similar contribution. Occasionally interstellar comets must pass through the inner solar system, but Whipple (1975) considers it unlikely that such a comet is among the known cases of apparently hyperbolic comets. Even so the upper limit for the density of unobserved interstellar comets is relatively high.In addition, we must consider the possibility that comets are a genuine component of interstellar medium, and that the Oort Cloud is merely a captured part of it (McCrea, 1975). Here we review various dynamical possibilities of two-way exchange of comet populations between the Solar System and the interstellar medium. We describe ways in which a traditional Oort Cloud (Oort, 1950) could be captured from the interstellar medium. However, we note that the so called Kuiper belt (Kuiper, 1951) of comets cannot arise through this process. Therefore we have to ask how necessary the concept of the yet unobserved Kuiper belt is for the theory of short period comets.There has been considerable debate about the question whether short period comets can be understood as a captured population of the Oort Cloud of comets or whether an additional source has to be postulated. The problem is made difficult by the long integration times of comet orbits through the age of the Solar System. It would be better to have an accurate treatment of comet-planet encounters in a statistical sense, in the form of cross sections, and to carry out Monte Carlo studies. Here we describe the plan of action and initial results of the work to derive cross sections by carrying out large numbers of comet — planet encounters and by deriving approximate analytic expressions for them. Initially comets follow parabolic orbits of arbitrary inclination and perihelion distance; cross sections are derived for obtaining orbits of given energy and inclination after the encounter. The results are used in subsequent work to make evolutionary models of the comet population.     

Evolution and saturation of Autowaves in photodissociation regions

The propagation of plane, cylindrical, and spherical waves in a thermally unstable gas–dust medium has been simulated numerically. As applied to the photodissociation regions near O and B stars, we take into account the interaction of ultraviolet radiation with dust grains and large polycyclic aromatic hydrocarbon molecules as well as the gas cooling through the excitation of СII ions and OI atoms and the deexcitation of rotational levels of CO molecules. The instability regions have been determined. The perturbation growth times corresponding to them are ~10³?10⁵ yr. We show that wave breaking occurs irrespective of the geometry of motion, while a perturbation in the form of a single pulse gives rise to a sequence of shock waves. The post-shock gas velocity is approximately 0.1?0.5 of the sound velocity, so that the autowaves can contribute noticeably to the observed velocity dispersion of the gas near the boundaries of HII regions. Two-dimensional simulations suggest that the presence of multiple shocks in a thermally unstable medium can accelerate significantly the destruction of preexisting isolated condensations.     

Gravitational instability for some astrophysical systems

The gravitational instability of an infinite homogeneous self-gravitating mixture through porous medium in the presence of a variable horizontal magnetic field varying in vertical directions has been considered to include, separately, the effects due to suspended particles and collisions between ionized and neutral components. The dispersion relations in both cases have been obtained. It has been found that Jeans's criterion of instability holds good even if the effects due to suspended particles, collisions, porosity, and variable magnetic field are considered.     

Is the Parker Instability a Viable Mechanism for the Formation of Giant Molecular Clouds?

The stratified interstellar medium has been known to be subject to the Parker instability, and the instability has been considered as a plausible mechanism for the formation of giant molecular clouds (GMCs). By presenting our recent efforts to understand the instability through linear analyses and numerical simulations, we raise a negative point of view that the Parker instability alone could not form GMCs.     

Magneto-gravitational instability of a rotating and finitely-conducting fluid

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.