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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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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Turbulence Heating ObserveR – satellite mission proposal

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Furthermore, energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. We summarize the THOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’. THOR has been selected by European Space Agency (ESA) for the study phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

The Evolution of Galaxies and Their Environment

The Third Teton Summer School on Astrophysics discussed the formation of galaxies, star formation in galaxies, galaxies and quasars at high red shift, and the intergalactic and intercluster medium and cooling flows. Observation and theoretical research on these topics was presented at the meeting and summaries of the contributed papers are included in this volume.

Hollenbach, David↗
NASA NTRS2016

Turbulence Heating ObserveR: - Satellite Mission Proposal

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earths magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space magnetosheath, shock, foreshock and pristine solar wind featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4). THOR has been selected by European Space Agency (ESA) for the study phase.

Vaivads, A.↗
NASA NTRS1990

Optical coronal emission lines from equilibrium and cooling plasmas

A calculation has been made of the emission from gas at temperature of about 10 to the 6th K due to optical coronal lines that result from fine structure transitions within the ground states of highly ionized atoms. These lines include the Forbidden Fe X 6374-A line, the Forbidden Fe XIV 5303-A line, and many other lines from stages of ionization of S, Ca, Fe, and Ni. The calculations are valid in the limit of very low density, and apply to the diffuse gas found in supernova remnants, the interstellar medium in galaxies, and intergalactic gas. It is found that the amount of optical coronal emission produced by a given amount of cooling gas is largely unaffected by changes in element abundances (provided the proportions of heavy elements remain the same).

Graney, Christopher M.↗
DOE OSTI2024

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect

An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 10 5 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies, on scales from ~ 1 kpc up to their respective virial radii (~ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to degree scales) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1974

Interstellar and intergalactic matter and radiation

A brief summary of recent studies of the interstellar medium is given. Most attention is then devoted to a review of the evidence for the presence of intergalactic matter and radiation in the universe. It is concluded that the only important constituents which may make a sizable contribution to the total mass-energy are intergalactic gas and condensed objects with a very high mass-to-light ratio. If the QSOs are not at cosmological distances, cold atomic hydrogen may still be the most important constituent and may contribute much more mass than do the galaxies. The X-ray observations still do not unambiguously show that very hot gas is present, though it is very likely on general grounds that some hot gas is present in clusters of galaxies. The question of whether or not large amounts of matter, enough to close the universe, are present, remains unsettled. From the theoretical standpoint the answer depends almost completely on the approach taken to the problem of galaxy formation and to the cosmological model which is favored.

Burbidge, G. R.↗
NASA NTRS1990

Expanding hydrodynamical jets crossing a galactic halo/intergalactic medium interface

Parameters within ranges that are plausible for radio sources are presently used to perform two-dimensional hydrodynamical calculations of axisymmetric, initially conical, jets whose initial propagation is through isothermal galactic halos with power-law density distributions; these emerge across a pressure-matched interface into a hotter, but less dense medium whose parameters are typical of an intracluster or intergalactic gas. Upon crossing this interface, the jets accelerate and focused toward cylindrical shapes having long, narrow cocoons.

Wiita, Paul J.↗
NASA NTRS1987

The theory of the Galactic magnetic field

The paper discusses the role of the magnetic field in determining the large scale structure and dynamics of the interstellar medium. It then discusses the origin and maintenance of the Galactic field. The two major competing theories are that the field is primordial and connected to an intergalactic field or that the field is removed from and regenerated within the Galaxy. Finally, cosmic ray acceleration and confinement in the interstellar medium are discussed.

Zweibel, Ellen G.↗
DOE OSTI2016

THE INTRAGROUP VERSUS THE INTRACLUSTER MEDIUM

Galaxy groups differ from clusters primarily by way of their lower masses, M ∼ 10{sup 14} M {sub ⊙} versus M ∼ 10{sup 15} M {sub ⊙}. We discuss how mass affects the thermal state of the intracluster or the intragroup medium, specifically as to their entropy levels and radial profiles. We show that entropy is produced in both cases by the continuing inflow of intergalactic gas across the system boundary into the gravitational potential well. The inflow is highly supersonic in clusters, but weakly so in groups. The former condition implies strong accretion shocks with substantial conversion of a large bulk kinetic into thermal energy, whereas the latter condition implies less effective conversion of lower energies. These features produce a conspicuous difference in entropy deposition at the current boundary. Thereafter, adiabatic compression of the hot gas into the potential well converts such time histories into radial profiles throughout a cluster or a group. In addition, in both cases, a location of the system at low z in the accelerating universe or in a poor environment will starve out the inflow and the entropy production and produce flattening or even bending down of the outer profile. We analyze, in detail, the sharp evidence provided by the two groups ESO 3060170 and RXJ1159+5531 that have been recently observed in X-rays out to their virial radii and find a close and detailed match with our expectations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Primordial random motions and angular momenta of galaxies and galaxy clusters.

We study the decay of primordial random motions of galaxies and galaxy clusters in an expanding universe by solving a kinetic equation for the relaxation of differential energy spectra N(E, t). Systematic dissipative energy losses are included, involving gravitational drag by, and accretion of, intergalactic matter, as well as the effect of collisions with other systems. Formal and numerical solutions are described for two distinct modes of galaxy formation in a turbulent medium, corresponding to formation at a distinct epoch and to continuous formation of galaxies. We show that any primordial random motions of galaxies at the present epoch can amount to at most a few km/sec, and that collisions at early epochs can lead to the acquisition of significant amounts of primordial angular momentum.

Silk, J.↗
DOE OSTI2016

The stacked Lyα emission profile from the circum-galactic medium of z ∼ 2 quasars

In the context of the FLASHLIGHT survey, we obtained deep narrowband images of 15 z ∼ 2 quasars with the Gemini Multi-object Spectrograph on Gemini South in an effort to measure Lyα emission from circum- and intergalactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Lyα nebulae (SB ∼ 10{sup −17} erg s{sup −1} cm{sup −2} arcsec{sup −2} at distances >50 kpc) around any of our sources, although we routinely (≃47%) detect smaller-scale <50 kpc Lyα emission at this surface brightness level emerging from either the extended narrow emission line regions powered by the quasars or by star formation in their host galaxies. We stack our 15 deep images to study the average extended Lyα surface brightness profile around z ∼ 2 quasars, carefully PSF-subtracting the unresolved emission component and paying close attention to sources of systematic error. Our analysis, which achieves an unprecedented depth, reveals a surface brightness of SB{sub Lyα} ∼ 10{sup −19} erg s{sup −1} cm{sup −2} arcsec{sup −2} at ∼200 kpc, with a 2.3σ detection of Lyα emission at SB {sub Lyα}=(5.5±3.1)×10{sup −20} erg s{sup −1} cm{sup −2} arcsec{sup −2} within an annulus spanning 50 kpc < R < 500 kpc from the quasars. Assuming that this Lyα emission is powered by fluorescence from highly ionized gas illuminated by the bright central quasar, we deduce an average volume density of n {sub H} = 0.6 × 10{sup −2} cm{sup −3} on these large scales. Our results are in broad agreement with the densities suggested by cosmological hydrodynamical simulations of massive (M ≃ 10{sup 12.5} M {sub ⊙}) quasar hosts; however, they indicate that the typical quasars at these redshifts are surrounded by gas that is a factor of ∼100 times less dense than the (∼1 cm{sup −3}) gas responsible for the giant bright Lyα nebulae around quasars recently discovered by our group.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

X-ray astronomy from Uhuru to HEAO-1

The nature of galactic and extragalactic X-ray sources is investigated using observations made with nine satellites and several rockets. The question of X-ray pulsars being neutron stars or white dwarfs is considered, as is the nature of Population II and low-luminosity X-ray stars, the diffuse X-ray emission from clusters of galaxies, the unidentified high-galactic-latitude (UHGL) sources, and the unresolved soft X-ray background. The types of sources examined include binary pulsars, Population II X-ray stars (both nonbursters and bursters) inside and outside globular clusters, coronal X-ray emitters, and active galactic nuclei. It is concluded that: (1) X-ray pulsars are strongly magnetized neutron stars formed in the evolution of massive close binaries; (2) all Population II X-ray stars are weakly magnetized or nonmagnetic neutron stars accreting from low-mass companions in close binary systems; (3) the diffuse emission from clusters is thermal bremsstrahlung of hot matter processed in stars and swept out by ram pressure exerted by the intergalactic gas; (4) most or all of the UHGL sources are active galactic nuclei; and (5) the soft X-ray background is emission from a hot component of the interstellar medium.

Clark, G. W.↗
NASA NTRS1995

Medium-resolution far-ultraviolet spectroscopy of PKS 2155-304

Using the Berkeley spectrometer of the Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS) we observed the 87-117 nm UV spectrum of the BL Lac object PKS 2155-304 with about 0.5 A resolution. In addition to the expected interstellar lines we detected higher quantum number counterparts of the intergalactic Lyman alpha lines discovered earlier with IUE and the Hubble Space Telescope (HST) in the direction of PKS 2155-304. The Lyman discontinuities indicate for three of the redshifted clouds a combined H I column density of 2-5 x 10(exp 16)/sq cm, while the column density for another cloud appears to be well below 5 x 10(exp 15)/sq cm. No siginificant O VI absorption in the galactic halo toward PKS 2155-304 could be detected from our data. Assuming that saturation effects are negligible for these weak features, we obtain for the O VI column density toward PKS 2155-304 a 3 sigma upper limit of 2.7 x 10(exp 14)/sq cm.

Appenzeller, I.↗
NASA NTRS1972

Theoretical models of photoionized intergalactic hydrogen.

The effects of ionizing radiation emitted by quasi-stellar objects on intergalactic hydrogen are studied. The hydrogen is assumed to expand with the Universe, and the amount of ionizing radiation is estimated from observations of the QSO luminosity function. The discreteness of the radiation sources is taken into account in computing the thermal history of the medium. The amount of ionizing radiation is shown to be sufficient to allow the existence of a universal medium with a temperature less than 10,000 K and a density several times the smeared-out density of luminous matter in galaxies. Such a medium would escape detection with presently available techniques.

Arons, J.↗
NASA NTRS1984

Studies of X-ray clusters of galaxies/intergalactic plasmas

Intergalactic plasmas were investigated from both an observational and theoretical point of view. A multiobject spectrometer, the MX spectrograph was used to obtain detailed dynamical information on clusters of galaxies; this information was then compared with X ray emission from hot gas in these clusters. Several spectra of galaxies are presented, and data reduction of the spectra was discussed. The existence of quasar winds in Seyfert galaxies and the interaction between such a wind and the interstellar medium also were considered.

Scott, J. S.↗
DOE OSTI2017

The Remarkable Similarity of Massive Galaxy Clusters from z ∼ 0 to z ∼ 1.9

We present the results of a Chandra X-ray survey of the eight most massive galaxy clusters at z > 1.2 in the South Pole Telescope 2500 deg{sup 2} survey. We combine this sample with previously published Chandra observations of 49 massive X-ray-selected clusters at 0 < z < 0.1 and 90 Sunyaev–Zel’dovich–selected clusters at 0.25 < z < 1.2 to constrain the evolution of the intracluster medium (ICM) over the past ∼10 Gyr. We find that the bulk of the ICM has evolved self-similarly over the full redshift range probed here, with the ICM density at r>0.2R{sub 500} scaling like E(z){sup 2}. In the centers of clusters (r≲0.01R{sub 500}), we find significant deviations from self-similarity (n{sub e}∝E(z){sup 0.2±0.5}), consistent with no redshift dependence. When we isolate clusters with overdense cores (i.e., cool cores), we find that the average overdensity profile has not evolved with redshift—that is, cool cores have not changed in size, density, or total mass over the past ∼9–10 Gyr. We show that the evolving “cuspiness” of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self-similarly evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to H(z){sup −1}.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Analysis of small-scale microwave background radiation anisotropy in the presence of foreground contamination

Many of the current round of experiments searching for anisotropies in the microwave background radiation (MBR) are confronting the problem of how to disentangle the cosmic signal from contamination due to Galactic and intergalactic foreground sources. Here we show how commonly used likelihood function techniques can be generalized to account for foreground. Specifically we set some restrictions on the spectrum of foreground contamination but allow the amplitude to vary arbitrarily. The likelihood function thus generalized gives reasonable limits on the MBR anisotropy which, in some cases, are not much less restrictive than what one would get from more detailed modeling of the foreground. Furthermore, the likelihood function is exactly the same as one would obtain by simply projecting out foreground contamination and looking at the reduced data set. We apply this generalized analysis to the recent medium-angle data sets of ACME-HEMT (Gaier et al. 1992; Schuster et al. 1993) and MAX (Meinhold et al. 1993; Gunderson et al. 1993). The resulting analysis constrains the one free parameter in the standard cold dark matter theory to be Q(sub rms-ps) = 18(sub -5 sup +8) microKelvin. This best fit value, although in striking agreement with the normalization from Cosmic Background Explorer (COBE), is not a very good fit, with an overall chi-squared/degrees of freedom = 208/168. We also argue against three commonly used methods of dealing with foreground: (1) ignoring it completely; (2) subtracting off a best-fit foreground and treating the residuals as if uncontaminated; and (3) culling data which appears to be contaminated by foreground.

Dodelson, Scott↗