Characteristics of damping of the pulses in the Sun

This paper is a sequel to our earlier paper on the mathematical modelling in determining the rotational frequency and the density of an ionized medium. The technique is based on the measurement of the group travel time for a wave propagating in a rotating ionized medium and finally a simple approximate formula determines the rotation and the density of the medium. The present paper calculates the damping of the pulse-waves in the rotating Sun and leads to a mathematical development to estimate more physical parameters of the solar system.     

Effects of cosmic rays and density inhomogeneity of the circumstellar medium on the formation of a supernova shell

We consider the self-similar problem of a supernova explosion in a radially inhomogeneous medium by taking into account the generation of accelerated relativistic particles. The initial density of the medium is assumed to decrease with distance from the explosion center as a power law, ρ ₀ = A/r ^θ. We use a two-fluid approach in which the total pressure in the medium is the sum of the circumstellar gas pressure and the relativistic particle pressure. The relativistic particle pressure at the shock front is specified as an external parameter. This approach is applicable in the case where the diffusion coefficient of accelerated particles is small and the thickness of the shock front is much smaller than its radius. We have numerically solved a system of ordinary differential equations for the dimensionless quantities that describe the velocity and density behind the shock front as well as the nonrelativistic gas and relativistic particle pressures for various parameters of the inhomogeneity of the medium and various compression ratios of the medium at the shock front. We have established that the shock acceleration of cosmic rays affects most strongly the formation of a supernova shell (making it thinner) in a homogeneous circumstellar medium. A decrease in the circumstellar matter density with distance from the explosion center causes the effect of shock-accelerated relativistic particles on the supernova shell formation to weaken considerably. Inhomogeneity of the medium makes the shell thicker and less dense, while an increase in the compression ratio of the medium at the shock front causes the shell to become thinner and denser. As the relativistic particle density increases, the effect of circumstellar matter inhomogeneity on the shell formation becomes weaker.     

The dynamics of the intergalactic medium

It is assumed that the intergalactic medium contains fully ionized plasmas. A detailed discussion shows that it is necessary to distinguish between medium-density and low-density plasmas before we can carry out any analysis. The conditions are very critical for the conclusions and application of any mechanism one likes to discuss for the intergalactic medium. It is shown that acceleration of high-energy particles in the intergalactic medium is possible.     

Unreddened stars and the two-phase model of the interstellar medium

We have computed two phase models of the interstellar medium, with cosmic rays and X-rays assumed to be the main ionizing agents, heating due to photoelectron ejection from the interstellar grains. We show that it is possible to have a hot and tenuous intercloud medium in pressure equilibrium with the interstellar clouds for a wide range of physical conditions, possibly existing in the interstellar space. The atomic and ionic line observations towards Sco are shown to be consistent with the origin of these lines in the intercloud medium for a range of values of the ionizing flux. It is suggested that the intercloud medium may be predominantly neutral, with ionization rates consistent with the limits imposed by molecular observations. The mean fractional ionization of the intercloud medium is 1%.On leave from Tata Institute of Fundamental Research, Bombay, India.     

Modification of the jeans instability criterion for fractal-structure astrophysical objects in the framework of nonextensive statistics

Unlike classical studies in which the gravitational instability criterion for astrophysical disks is derived in the framework of traditional kinetics or hydrodynamics, we propose to consider the totality of fluffy dust clusters of various astrophysical objects, in particular, protoplanetary subdisks, as a special type of continuous medium, i.e., fractal medium for which there are points and areas not filled with its components. Within the deformed Tsallis statistics formalism, which is intended to describe the behavior of anomalous systems with strong gravitational interaction and fractal nature of phase space, we derive, on the basis of the modified kinetic equation (with the collision integral in the Bhatnagar-Gross-Krook form), the generalized hydrodynamic Euler equations for a medium with the fractal mass dimension. Considering the linearization of the q-hydrodynamics equations, we investigate the instability of an infinitely homogeneous medium to obtain a simplified version of the modified gravitational instability criterion for an astrophysical disk with fractal structure.     

Formation of massive galaxies at the centre of a cluster

The formation of massive galaxies at the centre of a cluster is discussed here. The protogalaxies move with both rotation and random velocities through the gaseous medium pervading the cluster. Each galaxy is supposed to move through a resisting medium under the general gravitational field produced by the cluster as a whole. Also, the mass of the galaxy increases by accretion all the time as it moves through the medium. Using plausible laws for density of the medium and accretion of matter and solving equation of motion, we find that the galaxy loses angular momentum in the course of the time. The loss of angular momentum drives the galaxy towards the centre of the cluster. Thus over a sufficiently long time-scale several galaxies may merge in the central region of the cluster resulting in a single massive galaxy. The process can drive rise to several massive galaxies in the central region of the cluster.     

The structure of the IRAS05168+3634 star-forming region

Astrophysics and Space Science - Radioactive components of the interstellar medium provide an entirely-different and new aspect to the studies of the interstellar medium. Injected from sources of...     

Primordial condensation of meteorite components — Experimental evidence of the state of the source medium

Mineral grains and grain aggregates in meteorites carry potential information on the conditions in the environment where they formed. To avoid model-dependent interpretations it is necessary to develop experimental criteria that uniquely reflect the environmental parameters of interest. These parameters include the various temperatures of the source medium and the temperature of grains at growth, all of which are observed to be highly differentiated in the space medium in accordance with the radiation laws.Independent tests are also necessary to establish the chemical composition of the source medium which appears from the meteorite record to have been variable. Another important variable is the number density which is observed to span over more than twelve orders of magnitude in the domains in space where dust is being modified by condensation or evaporation.Metal diffusion couples in the interior of refractory mineral grains (melilite and spinel) indicate that these couples and their refractory host grains may have existed up to a year at 780 K. They could have supported temperatures lower than 900 K more than a day but cannot have formed at grain temperatures of the order of 1700 K as is assumed in some theories.The temperature parameters of the source medium are more difficult to determine from the record in meteorite minerals; assessments, in order to be realistic, have to be made within the bounds of the observed properties of the space medium. Kinetic isotope effects, imprinted together with nuclear effects on meteorite solids, provide a promising source of information on fractionation processes and on the state of excitation in the source medium. Theoretical and experimental verification of the isotope fractionation mechanisms, which may be responsible for the observed effects, are thus of importance.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978.     

A possible explanation for the radio afterglow of GRB 980519: the dense medium effect

GRB 980519 is characterized by its rapidly declining optical and X-ray afterglows. Explanations of this behaviour include models invoking a dense medium environment, which makes the shock wave evolve quickly into the subrelativistic phase, a jet-like outflow, and a wind-shaped circumburst medium environment. Recently, Frail et al. found that the latter two cases are consistent with the radio afterglow of this burst. Here, by considering the transrelativistic shock hydrodynamics, we show that the dense medium model can also account for the radio light curve quite well. The potential virtue of the dense medium model for GRB 980519 is that it implies a smaller angular size of the afterglow, which is essential for interpreting the strong modulation of the radio light curve. Optical extinction arising from the dense medium is not important if the prompt optical–UV flash accompanying the γ -ray emission can destroy dust by sublimation out to an appreciable distance. Comparisons with some other radio afterglows are also discussed.     

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.     

Two-component scattering model and the electron density spectrum

In this paper, we discuss a rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum. It is assumed that the interstellar scattering medium is composed of a thin-screen interstellar medium (ISM) and an extended interstellar medium. We consider the case that the scattering of the thin screen concentrates in a thin layer represented by a δ function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with the observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight (LOS). The theoretical modulation indices are comparatively less sensitive to the scattering strength of the thin-screen medium, but they critically depend on the distance from the observer to the thin screen. The logarithmic slope of the structure function is sensitive to the scattering strength of the thin-screen medium, but is relatively insensitive to the thin-screen location. Therefore, the proposed model can be applied to interpret the structure functions of flux density observed in pulsar PSR B2111 + 46 and PSR B0136 + 57. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the interstellar medium. Thus our work provides some insight into the distribution of the scattering along the LOS to the pulsar PSR B2111 + 46 and PSR B0136 + 57.     

A model for the tail region of the heliospheric interface

The physical processes in the tail of the region where the solar wind interacts with a partially ionized local interstellar medium are investigated in terms of a self-consistent kinetic-gas-dynamical model. Resonant charge exchange between hydrogen atoms and plasma protons is shown to cause the contact discontinuity to disappear far from the Sun. The solar wind plasma cools down and, as a result, the parameters of the plasma and hydrogen atoms approach the corresponding parameters of the unperturbed interstellar medium at large heliocentric distances.     

On the presence of graphite in the interstellar medium

The justification for the presence of graphite in the interstellar medium is examined. The conditions necessary for growth of graphite (single crystals) and other structurally disordered carbons are discussed. The effect of structural imperfections on the mechanical, thermal, electrical, magnetic, optic and chemical properties is illustrated. From this information it is concluded that the existence of graphite (single crystals) in the interstellar medium is unlikely. While various forms of highly disordered carbon grains may exist, none would satisfy the physical properties necessary to explain both polarization and extinction simultaneously.     

Wave disturbances near the temperature jump in the transition region of the solar atmosphere

We theoretically analyzed the properties of surface waves near the temperature jump in the solar atmosphere whose dispersion relation is identical in form to the equation for waves on deep water. We found an exact solution to the model equation for the vertical velocity of the medium in such a wave. Based on the derived space-time dependence of the vertical velocity of the medium, we quantitatively explained one of the events recorded in the SOI/MDI experiment onboard the SOHO spacecraft that accompanied coronal mass ejection.     

Magnetohydrodynamic effects on the growth of condensations in an expanding universe and the formation of galaxies

We review evidence for the existence of the Galaxy's (Milky Way's) magnetic field and the evidence for an intergalactic magnetic field permeating an ionized inter-galactic medium. The magnetohydrodynamics of such an inter-galactic medium during the post-recombination expansion and the effects of MHD on the formation of galaxies are then considered: isotropic cosmologies, the interaction of magnetic fields with isotropic backgrounds, detailed MHD perturbation computations, and an analysis of related MHD galaxyformation studies.     

On the description of a scattering medium by the number of particles scattered

We find the distribution in space and time of scatterers as a function of particles scattered in a one-dimensional rod under the influence of an incident pulse. For the steady-state case we find the distribution of scatterers according to the number of particles that are being scattered. This gives a condition for the validity of the binary collision approximation as well as information about the effect transported particles may have on a medium. We also show how to convert these results to the first Gaussian approximation to scattering in a three-dimensional plane-parallel medium.     

Chemical evolution of the intracluster gas

Recent X-ray observations have shown that intracluster medium has non-primordial composition. Iron lines have been detected. We present preliminary results on modelling of the chemical evolution of the intracluster medium in galaxy clusters. We consider in detail the galactic winds driven by supernovae, taking into account the binding energy of the galactic gas. We try to explain the metallicity gradient observed in the Perseus cluster from morphological segregation of galaxies in the inner part of the cluster.     

Prospects for Estimating the Properties of a Loose Surface from the Phase Profiles of Polarization and Intensity of the Scattered Light

It has been shown that the model of a scattering medium composed of clusters located in the far zones of each other allows some properties of regolith-like surfaces to be quantitatively estimated from the phase dependences of intensity and polarization measured in the backscattering domain. From the polarization profiles, the sizes of particles, the structure and porosity of the medium, and a portion of the surface area covered with a disperse material can be determined. At the same time, the intensity profiles of the scattered light weakly depend on the sizes and structure of particles; they are mainly controlled by the concentration of scatterers in the medium and the shadow-hiding contribution at small phase angles. Since the latter effect is beyond the considered model, a good agreement between the model and the measured intensity cannot be achieved. Nevertheless, if a portion of the surface that participates in coherent backscattering has been found from the phase profile of polarization, the present model makes it possible to determine the relative contribution of the shadow-hiding effect to the brightness surge measured at zero phase angle. This, in turn, may allow the roughness of the scattering surface to be estimated. The model contains no free parameters, but there is currently no possibility to verify it comprehensively by the data obtained in laboratory measurements of the samples with thoroughly controlled characteristics, because such measurements are rare for a wide range of the properties of particles in a medium, their packing density, and phase angles.

     

Galactic cosmic ray distribution in the simplest model of termination shock near the heliospheric boundaries

The termination shock at the heliospheric boundary is simulated in terms of a two-layer turbulent medium for which the average radial component of solar wind velocity is nonzero inside the heliosphere and zero for external magnetic inhomogeneities. Galactic cosmic rays (GCRs) are scattered more strongly in the solar wind than in the interstellar medium. A boundary value problem for density is defined to describe GCR propagation in the given two-layer medium. The exact analytical solution of it is derived. The phase density and GCR fluxes in the whole range of the particle energies, as well as the degree of anisotropy of high-energy GCRs, are determined. The qualitative agreement of theoretical calculations and observed GCR distributions is obtained. In particular, in the region near the termination shock, an increase in the high-energy particle density and a decrease in the low-energy particle density are observed.     

Analysis of the non-Gaussian spectra of interplanetary scintillations

The non-Gaussian intensity fluctuation spectra observed by Cohenet al. (1967) are analysed. Computations of the length scales derived from the phase autocorrelation functions using Buckley's method (1971, I) indicate that for a rms phase deviation of 4 radians or more the diffracting medium behaves as one with its phase structure having ‘inner’ and ‘outer’ scales of turbulent blobs or eddies which are present in a turbulent medium.