Free-free emission by intergalactic hydrogen.
Free-free emission by intergalactic hydrogen calculated for steady state and closed evolving models
GALACTIC EVOLUTION↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The origin and dynamical effects of the magnetic fields and cosmic rays in the disk of the Galaxy
Galactic magnetic fields and cosmic ray gas, investigating origin and dynamical effects
Parker, E. N.↗
New theory for giant loops.
Four very large, shell-shaped features are known from the surveys of radio emission from the Galaxy. It is suggested that the giant loops represent a class of nebulae, induced by supernova radiation as opposed to supernova ejecta. The model considered provides a qualitative explanation for the spectral and polarization properties of the radio emission from giant loops. The radio emitting electrons are part of the general cosmic ray gas and need not arise specifically in the supernova that produced the fossil Stroemgren sphere.
Brandt, J. C.↗
Dust cooling of hot gas.
The cooling rates of a hot gas by ion-grain collisions are shown to be significant at temperatures above 1 million K. The importance of this cooling mechanism in certain phases of supernova explosions is noted. High-temperature modifications of this cooling mechanism in astronomical sources are discussed. A cooling curve is plotted for collisionally ionized gas containing cosmic abundances of heavy elements and graphite grains.
Ostriker, J. P.↗
The effect of C/O ratio on the condensation of planetary material
The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the C/O ratio. As the ratio increases from 0.4 to 0.9, condensation temperatures of compounds such as Al2O3, Ca2Al2SiO7, MgAl2O4, Mg2SiO4, and MgSiO3 decrease by 50-100 degrees. As C/O increases from 0.9 to 1.0, these temperatures drop an additional 300-400 degrees. Other chemical differences result when C/O approximately equals or exceeds 0.9. A new suite of high-temperature minerals appears (graphite, CaS, Fe3C, SiC and TiN); the reaction CO + 3H2 yields CH4 + H2O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.
Larimer, J. W.↗
Volatile/mobile trace elements in Karoonda /C4/ chondrite
Concentrations of ten volatile/mobile trace elements and of nonvolatile Co in the Karoonda (C4) meteorite were determined, and the atomic abundances relative to C1 are compared with values for the Murchison (C2) and Allende (C3) meteorites. Empirical Bi, In, and Tl data for Karoonda and heated Allende and Murchison are compared with theoretical curves for condensation from a gas of cosmic composition at low pressures. It is suggested that Karoonda might derive from low-temperature open-system metamorphism of pristine C3-like material.
Matza, S. D.↗
Gamma rays from the magellanic clouds
Predicted gamma ray fluxes from the Megallanic Clouds, obtained by using updated parameters, are significantly above the values previously determined, and well within the capabilities of observation from COS-B satellite. Concepts relating galactic gamma ray production and other Population 1 phenomena in the Milky Way were used to postulate a factor of four increase in predicted flux, based on the galactic origin hypothesis. The values obtained provide a possible test of two interpretations of gamma ray emission: enhancement in the inner galaxy from gas and cosmic ray sources alone, or increases produced by the trapping of cosmic rays in spiral arms. Because spiral structure is absent in the small cloud, and questionable in the large cloud, and both clouds are classed as irregular galaxies, the predicted enhancement in gamma ray flux may not be as great in the absence of clear spiral structure.
Stecker, F. W.↗
Gamma-ray Astrophysics: a New Look at the Universe
Gamma-ray astronomy which includes the spectral region from above approximately 100 keV to greater than or equal to 1000 GeV permits investigation of the most energetic photons originating in our galaxy and beyond and provides the most direct means of studying the largest transfers of energy occurring in astrophysical processes. Of all the electromagnetic spectrum, high-energy gamma-ray astronomy measures most directly the presence and dynamic effects of the energetic charged cosmic ray particles, element synthesis, and particle acceleration. Further, gamma rays suffer negligible absorption or scatterings as they travel in straight paths; hence, they may survive billions of years and still reveal their source. The high energy processes in stellar objects (including our Sun), the dynamics of the cosmic-ray gas, the formation of clouds and nebulae, galactic evolution and even certain aspects of cosmology and the origin of the universe may be explored by gamma-ray observations.
Trombka, J. I.↗
The thermodynamics of dust formation - Evidence from meteorites
The paper examines the thermodynamics of dust formation indicated by meteorites. Much of interstellar dust probably formed in the nebulae around protostars, and mineralogy and composition of meteorites provides information that prevailed in the nebula. The fact that the gas associated with interstellar dust has solar H/S ratios indicates that FeS, which forms at 680 K, is not present in the dust, and since iron only becomes oxidized at even lower temperatures, oxidized iron is not expected in the dust. If most interstellar dust forms in the nebulae and is ejected back in space, a high temperature is indicated. High-temperature fractionation processes played an important role in the nebula, and much of the Al, Ca, and Ti evidently condensed and accreted into cm-sized objects, some of which are found in carbonaceous chondrites; they are explicable in terms of formation from a cooling neutral gas with cosmic composition.
Larimer, J. W.↗
Einstein observations of the X-ray structure of Centaurus A - Evidence for the radio-lobe energy source
The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.
Schreier, E. J.↗
The LDEF benefits
The Long Duration Exposure Facility (LDEF) is described, and experiments planned for the first LDEF mission are discussed. Four of the eight involve scientific studies of interstellar gas, micrometeoroids, cosmic rays, and crystal growth in zero gravity, and four involve technology studies of the space environmental effects on solar cells, composite materials, thermal coatings, fiber optics, and electronic instruments. For each experiment, the objectives and methods are discussed.
Kinard, W. H.↗
Soft X-ray opacity in hot and photoionized gases
New calculations are presented of the soft X-ray opacity of gas having cosmic elemental abundances, but in a variety of ionization states. Coronal ionization equilibrium is considered over the range of temperatures 10 to the 4th to 3 x 10 to the 8th K and photoionization equilibrium with power-law and thermal bremsstrahlung spectra over a wide range of ionization parameters. The results are displayed in illustrative figures. For temperatures and ionization parameters commonly found in astrophysical plasmas, the opacity (particularly to photons of equal to or less than 1 keV) can be diminished by substantial factors relative to the state in which all atoms are neutral. As the dominant ionization stages change, the positions and contrasts of prominent K-edges also change.
Krolik, J. H.↗
Cosmic ray anisotropies at high energies
The directional anisotropies of the energetic cosmic ray gas due to the relative motion between the observers frame and the one where the relativistic gas can be assumed isotropic is analyzed. The radiation fluxes formula in the former frame must follow as the Lorentz invariance of dp/E, where p, E are the 4-vector momentum-energy components; dp is the 3-volume element in the momentum space. The anisotropic flux shows in such a case an amplitude, in a rotating earth, smaller than the experimental measurements from say, EAS-arrays for primary particle energies larger than 1.E(14) eV. Further, it is shown that two consecutive Lorentz transformations among three inertial frames exhibit the violation of dp/E invariance between the first and the third systems of reference, due to the Wigner rotation. A discussion of this result in the context of the experimental anisotropic fluxes and its current interpretation is given.
Martinic, N. J.↗
Photoionization in the halo of the Galaxy
The ionizing radiation field in the halo is calculated and found to be dominated in the 13.6-45 eV range by light from O-B stars that escapes the disk, by planetary nebulae at 45-54 eV, by quasars and the Galactic soft X-ray background at 54-2000 eV, and by the extragalactic X-ray background at higher energies. Photoionization models are calculated with this radiation field incident on halo clouds of constant density for a variety of densities, for normal and depleted abundances, and with variations of the incident spectrum. For species at least triply ionized, such as Si IV, C IV, N V, and O VI, the line ratios are determined by intervening gas with the greatest volume, which is not necessarily the greatest mass component. Column densities from doubly ionized species like Si III should be greater than from triply ionized species. The role of photoionized gas in cosmic ray-supported halos and Galactic fountains is discussed. Observational tests of photoionization models are suggested.
Bregman, Joel N.↗
Fast dynamos, cosmic rays, and the Galactic magnetic field
It is suggested here that the dynamo believed to be responsible for the magnetic field of the Galaxy is a fast dynamo due to the dynamical reconnection of the azimuthal field of the Galaxy as the field is deformed by the instability of the gaseous disk and the rapid inflation of magnetic lobes by the cosmic-ray gas to form the Galactic halo. The reconnection of adjacent lobes carries out both the alpha effect and field dissipation essential for the existence of the Galactic alpha-omega dynamo. The azimuthal field is generated primarily in the gaseous disk, while the alpha effect is carried out in the halo.
Parker, E. N.↗
Mapping the Gas Turbulence in the Coma Cluster: Predictions for Astro-H
Astro-H will be able for the first time to map gas velocities and detect turbulence in galaxy clusters. One of the best targets for turbulence studies is the Coma cluster, due to its proximity, absence of a cool core, and lack of a central active galactic nucleus. To determine what constraints Astro-H will be able to place on the Coma velocity field, we construct simulated maps of the projected gas velocity and compute the second-order structure function, an analog of the velocity power spectrum. We vary the injection scale, dissipation scale, slope, and normalization of the turbulent power spectrum, and apply measurement errors and finite sampling to the velocity field. We find that even with sparse coverage of the cluster, Astro-H will be able to measure the Mach number and the injection scale of the turbulent power spectrum-the quantities determining the energy flux down the turbulent cascade and the diffusion rate for everything that is advected by the gas (metals, cosmic rays, etc.). Astro-H will not be sensitive to the dissipation scale or the slope of the power spectrum in its inertial range, unless they are outside physically motivated intervals. We give the expected confidence intervals for the injection scale and the normalization of the power spectrum for a number of possible pointing configurations, combining the structure function and velocity dispersion data. Importantly, we also determine that measurement errors on the line shift will bias the velocity structure function upward, and show how to correct this bias.
clusters: intracluster medium↗
Contact and pressure balance structures in two-fluid cosmic-ray hydrodynamics
The role of cosmic-ray-modified contact discontinuities and pressure balance structures in two-fluid cosmic-ray hydrodynamics in one Cartesian space dimension are investigated by means of analytic and numerical solution examples, as well as by weakly nonlinear asymptotics. The fundamental wave modes of the two-fluid cosmic-ray hydrodynamic equations in the long-wavelength limit consist of the backward and forward propagating cosmic-ray-modified sound waves, with sound speed dependent on both the cosmic-ray and thermal gas pressures; the contact discontinuity; and a pressure balance mode in which the sum ofthe cosmic ray and thermal gas pressure perturbations is zero. The pressure balance mode, like the contact discontinuity is advected with the background flow. The interaction of the pressure balance mode with the contact discontinuity is investigated by means of the method of multiple scales. The thermal gas and cosmic-ray pressure perturbations satisfy a linear diffusion equation, and entropy perturbations arising from nonisentropic initial conditions for the thermal gas are frozen into the fluid. The contact discontinuity and pressure balance eigenmodes both admit nonzero perturbations in the thermal gas, whereas the cosmic-ray-modified sound waves are isentropic. The total entropy perturbation is shared between the contact discontinuity and pressure balance eigenmodes, and examples are given in which there is a transfer of entropy between the two modes. In particular, N-wave type density disturbances are obtained which arise as a result of the entropy transfer between the two modes. A weakly nonlinear geometric optics perturbation expansion is used to study the long timescale evolution of the short-wavelength entropy wave and the thermal gas sound waves in a slowly varying, large-scale background flow. The weakly nonlinear geometric optics expansion is also used to generalize previous studies of squeezing instability for short-wavelength sound waves in the two fluid model, by including a weakly nonlinear wave steepening term that leads to shock formation, as well as the effect of long time and space dependence of the background flow. Implications of cosmic-ray-modified pressure balance structures and contact discontinuities in models of the interaction of traveling interplanetary shocks and compression and rarefraction waves with the solar wind termination shock are briefly discussed.
Webb, G. M.↗
Relevance of cosmic gamma rays to the mass of gas in the galaxy
The bulk of the diffuse gamma-ray flux comes from cosmic ray interactions in the interstellar medium. A knowledge of the large scale spatial distribution of the Galactic gamma-rays and the cosmic rays enables the distribution of the target gas to be examined. An approach of this type is used here to estimate the total mass of the molecular gas in the galaxy. It is shown to be much less than that previously derived, viz., approximately 6 x 10 to the 8th power solar masses within the solar radius as against approximately 3 x 10 to the 9th power based on 2.6 mm CO measurements.
Bhat, C. L.↗