Search NASA⌕ Search

SEARCH · Search NASA

Results for “INTERGALACTIC SPACE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Poynting Robertson Battery and the Chiral Magnetic Fields of AGN Jets

We propose that the magnetic fields in the accretion disks of active galactic nuclei (AGNs) are generated by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with the AGN photons (the Poynting Robertson battery). This process provides a unique relation between the polarity of the poloidal B field to the angular velocity Omega of the accretion disk (B is parallel to Omega), a relation absent in the more popular dynamo B-field generation. This then leads to a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry comes about by chance being approx.0.06 %. This lends support to the hypothesis that the universe is seeded by B fields that are generated in AGNs via this mechanism and subsequently injected into intergalactic space by the jet outflows.

Kazanas, Demosthenes↗
NASA NTRS2010

Science with the Square Kilometre Array

The Square Kilometre Array (SKA) is the centimeter- and meter-wavelength telescope for the 21st Century. Its Key Science Projects are (a) The end of the Dark Ages, involving searches for an H i signature and the first metalrich systems; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) Observations of H i to a redshift z ~ 2 from which to study the evolution of galaxies and dark energy. (d) Astrobiology including planetary formation within protoplanetary disks; and (c) The origin and evolution of cosmic magnetism, both within the Galaxy and in intergalactic space. The SKA will operate over the wavelength range of at least 1.2 cm to 4 m (70 MHz to 25 GHz), providing milliarcsecond resolution at the shortest wavelengths.

cosmic microwave↗
DOE OSTI2020

Effective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis

We measure the effective opacity (τ{sub eff}) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2 ≲ z ≲ 3. Our spectra are taken from the COSMOS Lyα Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Lyα forest, we measure the effective Lyα opacity (τ{sub eff}) in the 2.02 ≤ z ≤ 2.44 range. At z = 2.22, we estimate τ{sub eff} =0.159±0.001 from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z < 2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous τ{sub eff} measurements that describes the steep redshift evolution in τ{sub eff} from z = 1.5–4.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1996

Intergalactic Hydrogen Clouds at Low Redshift: Connections to Voids and Dwarf Galaxies

We provide new post-COSTAR data on one sightline (Mrk 421) and updated data from another (I Zw 1) from our Hubble Space Telescope (HST) survey of intergalactic Ly(alpha) clouds located along sightlines to four bright quasars passing through well-mapped galaxy voids (16000 km/s pathlength) and superclusters (18000 km/s). We report two more definite detections of low-redshift Ly(alpha) clouds in voids: one at 3047 km/s (heliocentric) toward Mrk 421 and a second just beyond the Local Supercluster at 2861 km/s toward I Zw 1, confirming our earlier discovery of Ly(alpha) absorption clouds in voids (Stocke et al., ApJ, 451, 24). We have now identified ten definite and one probable low-redshift neutral hydrogen absorption clouds toward four targets, a frequency of approximately one absorber every 3400 km/s above 10(exp 12.7/sq cm column density. Of these ten absorption systems, three lie within voids; the probable absorber also lies in a void. Thus, the tendency of Ly(alpha) absorbers to 'avoid the voids' is not as clear as we found previously. If the Ly(alpha) clouds are approximated as homogeneous spheres of 100 kpc radius, their masses are approximately 10(exp 9)solar mass (about 0.01 times that of bright L* galaxies) and they are 40 times more numerous, comparable to the density of dwarf galaxies and of low-mass halos in numerical CDM simulations. The Ly(alpha) clouds contribute a fraction Omega(sub cl)approximately equals 0.003/h(sub 75) to the closure density of the universe, comparable to that of luminous matter. These clouds probably require a substantial amount of nonbaryonic dark matter for gravitational binding. They may represent extended haloes of low-mass protogalaxies which have not experienced significant star formation or low-mass dwarf galaxies whose star formation ceased long ago, but blew out significant gaseous material.

Shull, J. Michael↗
NASA NTRS1985

Hoop/column antenna deployment mechanism overview

The hoop/column antenna program is directed toward the development of a cost effective, large area, self deploying reflector antenna system. Large surface area antenna systems are required in future space missions involving improved land communications, Earth resources observation, and the study of intergalactic energy sources. The hoop/column antenna is a concept where a large antenna system can be packaged within the Space Transportation System (Shuttle) payload bay, launched into Earth orbit where it is released either for deployment as an Earth observation or communications antenna, or boosted into deep space as an intergalactic energy probe. Various mechanisms and support structures are described that are required to deploy the hoop, which is used to support the antenna reflective surface, and the column that is used to position the antenna feeds and the reflector. It also describes a proof-of-concept model (15 meters in diameter) that is currently being ground tested to determine the adequacy of the deployment mechanisms.

Allen, B. B.↗
NASA NTRS2023

Performance of High-Resolution Mo/Cu Transition Edge Sensors Fabricated Using a Lift-Off Process

The soft X-ray band below ≈0.5 keV is expected to provide rich information on metallicity, temperature, and distribution of hot gas in our galaxy and the intergalactic medium. Resolving these densely spaced emission lines requires energy resolution on the order of 1--2 eV. The low count rates from diffuse astrophysical sources also necessitate large collection areas, particularly for a sounding rocket instrument with short exposure times and limited resources. This translates to large pixel sizes (about 1 mm 2 ) for a reasonable number of read-out channels. To achieve the required energy resolution with 200 nm thin Au absorbers (heat capacity C about 1 pJ/K), we are developing TES microcalorimeters with very high temperature sensitivity (αI), low enough current sensitivity (βI), and minimal excess noise (M). Out of the various fabrication approaches for the TES bilayer we have explored, the lift-off approach (as pioneered for Mo/Au TES by Joel Weber at NIST) so far is the simplest to execute. The simple square TES geometries we have tested to date show promising results for αI and βI. Measured complex impedance and noise for bare devices without absorbers are well described by two-body thermal models and their excess noise is found to be consistent with predictions for mixed-down Johnson noise by Wessels et al. More sensitive measurements with larger heat capacity are planned to accurately determine excess noise. In this paper, we give an overview of the process and summarize results of our detailed characterization measurements for thermal conductance G, αI, βI, and noise for several devices across a range of bias points.

Felix T Jaeckel↗
NASA NTRS1995

Intergalactic Helium Absorption toward High-Redshift Quasars

The recent Hubble Space Telescope (HST) observations of the z(q) = 3.286 quasar Q0302-003 (Jakobsen et at. 1994) and the z(q) = 3.185 quasar Q1935-67 by Tytler (1995) show absorption edges at the redshifted wavelength of He II 304 A. A key goal is to distinguish between contributions from discrete Ly-alpha forest clouds and a smoothly distributed intergalactic medium (IGM). We model the contributions from each of these sources of He II absorption, including the distribution of line Doppler widths and column densities, the 'He II proximity effect' from the quasar, and a self-consistent derivation of the He II opacity of the universe as a function of the spectrum of ionizing sources, with the assumption that both the clouds and the IGM are photoionized. The He II edge can be fully accounted for by He II line blanketing for reasonable distributions of line widths and column densities in the Ly-alpha forest, provided that the ionizing sources have spectral index alpha(s) greater than 1.5, and any He II proximity effect is neglected. Even with some contribution from a diffuse IGM, it is difficult to account for the edge observed by Jakobsen et al. (1994) with a 'hard' source spectrum (alpha(s) less than 1.3). The proximity effect modifies the relative contributions of the clouds and IGM to tau(He II) near the quasar (z approx. less than z(q)) and markedly increases the amount of He II absorption required. This implies, for example, that to account for the He II edge with line blanketing alone, the minimum spectral index alpha(s) must be increased from 1.5 to 1.9. We demonstrate the need for higher resolution observations that characterize the change in transmission as z approaches z(q) and resolve line-free gaps in the continuum. We set limits on the density of the diffuse IGM and suggest that the IGM and Ly-alpha clouds are likely to be a significant repository for dark baryons.

Giroux, Mark L.↗
DOE OSTI2024

Probing New physics with high-redshift quasars: axions and non-standard cosmology

The Hubble diagram of quasars, as candidates to “standardizable” candles, has been used to measure the expansion history of the Universe at late times, up to very high redshifts ( z ~ 7). It has been shown that this history, as inferred from the quasar dataset, deviates at ≳ 3 σ level from the concordance (ΛCDM) cosmology model preferred by the cosmic microwave background (CMB) and other datasets. In this article, we investigate whether new physics beyond ΛCDM (BΛCDM) or beyond the Standard Model (BSM) could make the quasar data consistent with the concordance model. We first show that an effective redshift-dependent relation between the quasar UV and X-ray luminosities, complementing previous phenomenological work in the literature, can potentially remedy the discrepancy. Such a redshift dependence can be realized in a BSM model with axion-photon conversion in the intergalactic medium (IGM), although the preferred parameter space is in tension with various other astrophysical constraints on axions, at a level depending on the specific assumptions made regarding the IGM magnetic field. We briefly discuss a variation of the axion model that could evade these astrophysical constraints. On the other hand, we show that models beyond ΛCDM such as one with a varying dark energy equation of state ( w CDM) or the phenomenological cosmographic model with a polynomial expansion of the luminosity distance, cannot alleviate the tension. The code for our analysis, based on emcee [1] and corner.py [2], is publicly available at github.com/ChenSun-Phys/high_z_candles.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Intergalactic thermonuclear gamma-ray line

The possibility of thermonculear reactions occurring in dilute space is briefly considered. X-ray emission from clusters of galaxies demonstrates that perhaps as much as 10 to the 14th solar masses of hot gas (T of about 100 million K) may often surround galaxies in clusters with a density of perhaps 0.004/cu cm. If the ion temperature is 100 million K, the thermonuclear reaction p + d to He-3 + gamma ray should emit gamma rays at a rate of roughly 4 x 10 to the 41st/sec with energy 5.516 + or -0.016 MeV. Such a source in teh virgo cluster at 15.7 Mpc would present a line flux of 1 x 10 to the -11th/sq cm/sec.

Clayton, D. D.↗
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 NTRS2005

Weighing the Low-Redshift Lyman-alpha Forest

In 2003-2004, our FUSE research group prepared several major surveys of the amount of baryonic matter in the intergalactic medium (IGM), using the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. These surveys include measurements of the Lyman-alpha absorption line of neutral hydrogen (H I), the far-ultraviolet (1032,1038 Angstrom) doublet of highly ionized oxygen ( O VI), the higher Lyman-series lines (Ly-beta, Ly-gamma, etc) of H I, and the 977 Angstrom line of c III. As an overview, our FUSE spectroscopic studies, taken together with data from the Hubble Space Telescope, show that approximately 30% of the normal matter is contained in intergalactic hydrogen gas clouds (the Lyman-alpha forest). Another 5-10% resides in hotter gas at temperatures of 10(exp 5) to 10(exp 6) K, visible in 0 VI and C III absorption. Along with the matter attributed to galaxies, we have now accounted for approximately HALF of all the baryonic matter in the universe. Where is the other half? That matter my exist in even hotter gas, invisible through the ultraviolet absorption lines, but perhaps detectable through X-ray absorption lines of more highly ionized oxygen and neon.

Shull, Mike↗
NASA NTRS2012

The Legacy of the FUSE Mission

The Far Ultraviolet Spectroscopic Explorer (FUSE) mission was a far-ultraviolet space telescope that performed high resolution (R=20,OOO) spectroscopy in the 905 - 1187 A spectral range. FUSE primarily observed stars and distant galaxies to study interstellar and intergalactic gas through absorption spectroscopy, as well as the properties of the objects themselves. This capability complemented the Hubble Space Telescope at longer wavelengths, and provided the international astronomical community with access to an important part of the electromagnetic spectrum. FUSE was a joint project of NASA, CNES, and CSA. The mission operated from 1999 to 2007. This review talk will summarize the scientific impact of the FUSE mission on several key scientific problems, as well as lessons learned for future mission concepts.

Sonneborne, George↗
NASA NTRS2010

The Hubble Space Telescope: UV, Visible, and Near-Infrared Pursuits

The Hubble Space Telescope continues to push the limits on world-class astrophysics. Cameras including the Advanced Camera for Surveys and the new panchromatic Wide Field Camera 3 which was installed nu last year's successful servicing mission S2N4,o{fer imaging from near-infrared through ultraviolet wavelengths. Spectroscopic studies of sources from black holes to exoplanet atmospheres are making great advances through the versatile use of STIS, the Space Telescope Imaging Spectrograph. The new Cosmic Origins Spectrograph, also installed last year, is the most sensitive UV spectrograph to fly io space and is uniquely suited to address particular scientific questions on galaxy halos, the intergalactic medium, and the cosmic web. With these outstanding capabilities on HST come complex needs for laboratory astrophysics support including atomic and line identification data. I will provide an overview of Hubble's current capabilities and the scientific programs and goals that particularly benefit from the studies of laboratory astrophysics.

Wiseman, Jennifer↗
DOE OSTI2025

Constraints on dark photon dark matter from Lyman- α forest simulations and an ultrahigh signal-to-noise quasar spectrum

The ultralight dark photon is a well-motivated, hypothetical dark matter candidate. In a dilute plasma, they can resonantly convert into photons, and heat up the intergalactic medium between galaxies. In this work, we explore the dark photon dark matter parameter space by comparing synthetic Lyman- α forest data from cosmological hydrodynamical simulations to observational data from VLT/UVES of the quasar HE0940-1050 ( z em = 3.09 ). We use a novel flux normalization technique that targets underdense gas, reshaping the flux probability distribution. Not only do we place robust constraints on the kinetic mixing parameter of dark photon dark matter, but notably our findings suggest that this model can still reconcile simulated and observed Doppler parameter distributions of z ∼ 0 Lyman- α lines, as seen by HST/COS. This work opens new pathways for the use of the Lyman- α forest to explore new physics, and can be extended to other scenarios such as primordial black hole evaporation, dark matter decay, and annihilation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1979

Field resonance propulsion concept

A propulsion concept was developed based on a proposed resonance between coherent, pulsed electromagnetic wave forms, and gravitational wave forms (or space-time metrics). Using this concept a spacecraft propulsion system potentially capable of galactic and intergalactic travel without prohibitive travel times was designed. The propulsion system utilizes recent research associated with magnetic field line merging, hydromagnetic wave effects, free-electron lasers, laser generation of megagauss fields, and special structural and containment metals. The research required to determine potential, field resonance characteristics and to evaluate various aspects of the spacecraft propulsion design is described.

Holt, A. C.↗
DOE OSTI2023

Cosmic variance and the inhomogeneous UV luminosity function of galaxies during reionization

When the first galaxies formed and starlight escaped into the intergalactic medium to reionize it, galaxy formation and reionization were both highly inhomogeneous in time and space, and fully coupled by mutual feedback. To show how this imprinted the UV luminosity function (UVLF) of reionization-era galaxies, we use our large-scale, radiation-hydrodynamics simulation CoDa II to derive the time- and space-varying halo mass function and UVLF, from z ≃ 6–15. That UVLF correlates strongly with local reionization redshift: earlier-reionizing regions have UVLFs that are higher, more extended to brighter magnitudes, and flatter at the faint end than later-reionizing regions observed at the same z. In general, as a region reionizes, the faint-end slope of its local UVLF flattens, and, by z = 6 (when reionization ended), the global UVLF, too, exhibits a flattened faint-end slope, ‘rolling-over’ at M UV ≳ -17. CoDa II’s UVLF is broadly consistent with cluster-lensed galaxy observations of the Hubble Frontier Fields at z = 6–8, including the faint end, except for the faintest data point at z = 6, based on one galaxy at M UV = -12.5. According to CoDa II, the probability of observing the latter is $\sim 5~{{\ \rm per\ cent}}$. However, the effective volume searched at this magnitude is very small, and is thus subject to significant cosmic variance. Here, we find that previous methods adopted to calculate the uncertainty due to cosmic variance underestimated it on such small scales by a factor of 2–4, primarily by underestimating the variance in halo abundance when the sample volume is small.

79 ASTRONOMY AND ASTROPHYSICS↗