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Evidence is presented for the emergence of a measurable anomalous cosmic-ray hydrogen component in 1987 which may account for 20-40 percent of the total hydrogen flux at 60 MeV. Comparing this flux with that of anomalous cosmic-ray helium, the H I/He I ratio in the very local interstellar medium is estimated at 4, consistent with determinations from solar ultraviolet backscatter measurements.
The most fundamental issue in the theory of cosmic strings is addressed by means of Numerical Simulations: the existence of a scaling solution. The resolution of this question will determine whether cosmic strings can form the basis of an attractive theory of galaxy formation or prove to be a cosmological disaster like magnetic monopoles or domain walls. After a brief discussion of our numerical technique, results are presented which, though still preliminary, offer the best support to date of this scaling hypothesis.
The transport of cosmic rays in the ISM is reviewed, with emphasis on interactions with the turbulent interstellar magnetic field. The standard picture of cosmic-ray transport suggests strongly the existence of a smooth turbulence spectrum over the range of scales between 10 to the 12th and 10 to the 19th cm. This, coupled with observations of radio wave scattering and other direct measurements, suggests a smooth, power-law turbulence spectrum over the range of scales from 10 to the 9th to 10 to the 19th cm, with the index of the power law being close to that of the Kolmogorov equilibrium subrange.
Babul et al. (1987) proposed that some gamma-ray bursts may be caused by energy released at the cusps of oscillating loops made of superconducting cosmic strings. It is claimed that there were some errors and omissions in that work, which are claimed to be corrected in the present paper. Arguments are presented, that given certain assumptions, the cusps on oscillating superconducting cosmic strings produce highly collimated and energetic electromagnetic bursts and that a fair fraction of electromagnetic energy is likely to come out as gamma rays.
These are the results of a numerical simulation of the formation of large-scale structure from cosmic-string loops in a universe dominated by massive neutrinos (hot dark matter). This model has several desirable features. The final matter distribution contains isolated density peaks embedded in a smooth background, producing a natural bias in the distribution of luminous matter. Because baryons can accrete onto the cosmic strings before the neutrinos, the galaxies will have baryon cores and dark neutrino halos. Galaxy formation in this model begins much earlier than in random-phase models. On large scales the distribution of clustered matter visually resembles the CfA survey, with large voids and filaments.
The spectrum of antiprotons from dark matter annihilation are calculated using the Lund Monte Carlo program, and simple analytic expressions for the spectrum and low-energy antiproton/proton ratio are derived. Comparing the results with recent upper limits on low energy antiprotons, it is concluded that the reported 4-13 GeV antiproton flux cannot be accounted for by dark matter annihilation. The new upper limits do not provide useful constraints on dark matter particles. They restrict the annihilation rate and imply that annihilation gamma ray and e(+) fluxes would be far below the fluxes produced by cosmic-ray collisions. It may be possible to look for a dark matter halo annihilation signal at antiprotons energies below 0.5 GeV, where the flux from cosmic-ray collisions is expected to be negligible.
The process of generating large-scale cosmic structure from the radiation-pressure or 'mock gravity' instability is studied with particular emphasis on the implications of the Berkeley-Nagoya rocket data for the submillimeter background. The linear theory of perturbations in an absorbing medium embedded in an expanding universe of radiation sources is presented. The instability sets up collapse velocities in linear perturbation theory which far exceed those from gravitational instability, so growth continues even after the instability switches off. Perturbation due to this effect is analyzed and related to the growth of large-scale cosmic structures at recent times; large-scale structure is shown to evolve very little from 1 + z about 5 to the present. Nonlinear small-scale effects of the instability are analyzed; it is shown that radiation pressure would compress gas into small, dense pressure-confined clouds with tau much greater than one.
Equations describing the transport of cosmic rays in relativistic flows in the diffusion approximation are obtained. The analysis is based on the zeroth, first, and second differential moment equations of the relativistic Boltzmann equation with a BGK collision term. A perturbation solution of the moment equations in the diffusion approximation yields both the co-moving frame particle current and viscous stresses. The resultant cosmic-ray continuity equation contains three readily recognized energy change terms: the adiabatic energy change term; the viscous shear energy change term; and a term proportional to the scalar product of the acceleration vector of the scattering frame and the heat flux.
Published measurement data on the production C-13 during interstellar propagation of cosmic rays (Webber et al., 1987; Guzik et al., 1985) are combined with observational data to determine the relative abundance of C-13 in the cosmic-ray source. The theoretical basis and implementation of the calculations are described in detail, and the results are presented in graphs. (C-13)/(C-12) is estimated as 0.003 + or - 0.005, consistent with the solar ratio (0.011), not consistent with the local abundance ratio (0.023), and in agreement with the source ratio predicted by Prantzos et al. (1985) using the isotopic abundances of WR-star ejecta.
The current understanding of cosmic string evolution is discussed, and the focus placed on the question of small scale structure on strings, where most of the disagreements lie. A physical picture designed to put the role of the small scale structure into more intuitive terms is presented. In this picture it can be seen how the small scale structure can feed back in a major way on the overall scaling solution. It is also argued that it is easy for small scale numerical errors to feed back in just such a way. The intuitive discussion presented here may form the basis for an analytic treatment of the small scale structure, which argued in any case would be extremely valuable in filling the gaps in the present understanding of cosmic string evolution.
Research activities in cosmic rays, gamma rays, and astrophysical plasmas are covered. The activities are divided into sections and described, followed by a bibliography. The astrophysical aspects of cosmic rays, gamma rays, and of the radiation and electromagnetic field environment of the Earth and other planets are investigated. These investigations are performed by means of energetic particle and photon detector systems flown on spacecraft and balloons.
The science objectives are summarized for the Cosmic Dust Collection Facility (CDCF) on Space Station Freedom and these objectives are related to ongoing science programs and mission planning within NASA. The purpose is to illustrate the potential of the CDCF project within the broad context of early solar system sciences that emphasize the study of primitive objects in state-of-the-art analytical and experimental laboratories on Earth. Current knowledge about the sources of cosmic dust and their associated orbital dynamics is examined, and the results are reviewed of modern microanalytical investigations of extraterrestrial dust particles collected on Earth. Major areas of scientific inquiry and uncertainty are identified and it is shown how CDCF will contribute to their solution. General facility and instrument concepts that need to be pursued are introduced, and the major development tasks that are needed to attain the scientific objectives of the CDCF project are identified.
COBE, the Cosmic Background Explorer spacecraft, and its mission are described. COBE was designed to study the origin and dynamics of the universe including the theory that the universe began with a cataclysmic explosion referred to as the Big Bang. To this end, earth's cosmic background - the infrared radiation that bombards earth from every direction - will be measured by three sophisticated instruments: the Differential Microwave Radiometer (DMR), the Far Infrared Absolute Spectrophotometer (FIRAS), and the Diffuse Infrared Background Experiment (DIRBE).
In a Sikivie-type cosmic-axion detector, both the width and position of the microwave signal due to axion-photon conversion depend upon the motions of the earth. Due to the orbital and rotational motions of the earth they will be modulated with periods of 1 sidereal day and 1 sidereal year, with amplitudes of about 0.1 percent and 5 percent respectively. Because of the intrinsically-high energy resolution of Sikivie-type detectors such periodic variations should be detectable. Such modulations would not only aid in confirming the detection of cosmic axions, but, if found, would also provide important information about the distribution of axions in the halo.
Cosmic-ray transport near discontinuities in the background fluid velocity is considered. Matching conditions for the cosmic-ray distribution are derived for both shear and compressive (shock) discontinuities, keeping terms to second order in the ratio of fluid speed to energetic-particle speed. Acceleration is found at shear discontinuities, which is not present in the first-order theory, and a modification of the matching condition at shocks. If there is no particle source concentrated at a shock, the new condition reduces to that obtained from first-order theory. Monte Carlo simulations show good agreement with the theory.
Measurements of the composition of the cosmic rays at high energies, and of the energy spectra of the individual components provide the basis for the understanding of the sources, of the acceleration mechanism, and of the galactic containment of these particles. A brief review of the presently available information and a recent measurement performed on the Space Shuttle to substantially extend the range of energies in which the elemental composition is known are described. Results, and recent data on the electron component of cosmic rays are discussed and summarized. The body of data now available contains several features that are difficult to explain within current models of galactic shock acceleration and 'leakly box' containment. The need for further measurements is emphasized and possible opportunities for future work are briefly discussed.
A brief description of the experiments carried out so far to measure the energy spectrum of antiprotons is made and the reason for the excitement in this field of research is elucidated. The observed spectrum appears to be different form the other components of cosmic rays. Various physical processes by which antiprotons could be created are summarized. The equilibrium spectrum of antiprotons in the Galaxy, arising from each of these processes, is derived for different propagation models. It is shown that no single model can predict correctly the observed data over the entire energy region. However, the recent data at low energies suggest that the conventional models with large amount of matter traversal by cosmic rays, either in the source region or during propagation, can reproduce the data closely. The implications of these propagation models for other components are discussed and the need for more observations is emphasized.
An analysis is presented that, for the first time, systematically normalizes the data from the HEAO 3 heavy nuclei experiment on the cosmic-ray abundances of all the elements heavier than germanium to that of iron. In the range of atomic number Z from 33 to 60, the analysis yields abundances of odd-even element pairs. The abundances are consistent with a cosmic-ray source having a composition similar to that of the solar system, but subject to source fractionation correlated with the first ionization potential (FIP) of each element. For Z greater than 60, the analysis yields abundances of element groups. For these heaviest nuclei, we find an enhancement of the abundance of the platinum group, elements with Z of 74-80, relative to that in propagated solar system source, and a corresponding increase in the abundance of the largely secondary elements in the 62-73 range. These abundances suggest that there is an enhancement of the r-process contribution to the source nuclei in the Z greater than 60 charge region. Over the entire region of charge, standard leaky box models of propagation satisfactorily model secondary production.