Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “galactic winds”

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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

XRISM Finds the Changing-look Active Galactic Nucleus NGC 1365 in an Extended Low State: A Dense, Highly Ionized Outflow Obscures the Central Source

We present the first XRISM/Resolve observations of the active galactic nucleus NGC 1365, obtained in 2024 February and July. NGC 1365 is known for rapid transitions between Compton-thick and Compton-thin states, along with strong absorption from a highly ionized wind. During our observations, the source was found in a persistent low-flux state, characterized by a decrease in hard-X-ray luminosity and significant line-of-sight obscuration. In this state, XRISM/Resolve reveals clear Fe XXV and Fe XXVI absorption lines together with, for the first time in this source, corresponding emission lines. These features may arise either from reemission from a photoionized wind (P Cygni profile) or from collisionally ionized gas associated with outflow-driven shocks in the interstellar medium. We estimate the wind launch radius to be approximately 10 16 cm (∼10 4 R g ), consistent with the location of the X-ray broadline region. We also resolve a broadened Fe Kα line by σ ∼ 1300 km s −1 , placing it at similar scales to the wind, consistent with radii inferred from disk-broadening models and the variability of the Fe Kα broad line. The similarity of the Fe Kα profile to the Hβ wing and broad Paα width indicates that the X-ray-emitting region is likely cospatial with the optical/infrared broadline region and originates from the same gas.

Astronomy and AstroPhysics↗
NASA NTRS1996

Ra: The Sun for Science and Humanity

To guide the development of the Ra Strategic Framework, we defined scientific and applications objectives. For our primary areas of scientific interest, we choose the corona, the solar wind, the Sun's effect on the Earth, and solar theory and model development. For secondary areas of scientific interest, we selected sunspots, the solar constant, the Sun's gravitational field, helioseismology and the galactic cosmic rays. We stress the importance of stereoscopic imaging, observations at high spatial, spectral, and temporal resolutions, as well as of long duration measurements. Further exploration of the Sun's polar regions is also important, as shown already by the Ulysses mission. From an applications perspective, we adopted three broad objectives that would derive complementary inputs for the Strategic Framework. These were to identify and investigate: possible application spin-offs from science missions, possible solar-terrestrial missions dedicated to a particular application, and possible future applications that require technology development. The Sun can be viewed as both a source of resources and of threats. Our principal applications focus was that of threat mitigation, by examining ways to improve solar threat monitoring and early warning systems. We compared these objectives to the mission objectives of past, current, and planned international solar missions. Past missions (1962-1980) seem to have been focused on improvement of scientific knowledge, using multiple instrument spacecraft. A ten year gap followed this period, during which the results from previous missions were analyzed and solar study programmes were prepared in international organizations. Current missions (1990-1996) focus on particular topics such as the corona, solar flares, and coronal mass ejections. In planned missions, Sun/Earth interactions and environmental effects of solar activity are becoming more important. The corona is the centre of interest of almost all planned missions. It seems that no international long-term strategy has yet been adopted. For these plans the number of necessary future missions can be reduced and the onboard instrumentation can be optimized by performing a comparative analysis. The study of the corona must be done from different observing locations, orbits closer to the Sun, and by different means. The Cluster mission replacement is in progress; however, if the replacement is not implemented, the ISTP programme will fade after 1998. Furthermore, the physics of the Sun's interior should be emphasized more in the Mid- and Far-Term programmes. Finally, more emphasis should be placed on monitoring space weather and forecasting Sun/Earth interactions.

Source record↗
NASA NTRS2018

Magnetized Disk Winds in NGC 3783

We analyze a 900 kilosecond stacked Chandra/HETG (High-Energy Transmission Grating) spectrum of NGC 3783 in the context of magnetically driven accretion-disk wind models in an effort to provide tight constraints on the global conditions of the underlying absorbers. Motivated by the earlier measurements of its absorption measure distribution (AMD) indicating X-ray-absorbing ionic columns that decrease slowly with decreasing ionization parameter, we employ 2-dimension (2-D) magnetohydrodynamic (MHD) disk wind models to describe the global outflow. We compute its photoionization structure along with the wind kinematic properties, allowing us to further calculate in a self-consistent fashion the shapes of the major X-ray absorption lines. With the wind radial density profile determined by the AMD, the profiles of the ensemble of the observed absorption features are determined by the two global parameters of the MHD wind; i.e., disk inclination theta (sub obs) and wind density normalization n (sub o). Considering the most significant absorption features in the approximately 1.8-20 angstrom range, we show that the MHD wind is best described by n(r) approximately equal to 6.9 times 10 (sup 11) (r/r (sub o)) (sup - 1.15) cubic centimeters and theta (sub obs). We argue that winds launched by X-ray heating or radiation pressure, or even MHD winds but with steeper radial density profiles, are strongly disfavored by data. Considering the properties of Fe K-band absorption features (i.e., Fe XXV and Fe XXVI), while typically prominent in the active galactic nucleus X-ray spectra, they appear to be weak in NGC 3783. For the specific parameters of our model obtained by fitting the AMD and the rest of the absorption features, these features are found to be weak, in agreement with observations.

Fukumura, Keigo↗
NASA NTRS2024

SOFIA/HAWC+ Far-Infrared Polarimetric Large-area CMZ Exploration Survey. III. Full Survey Data Set

We present the second data release (DR2) of the Far-InfraREd Polarimetric Large-Area CMZ Exploration (FIREPLACE) survey. This survey utilized the Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera plus instrument at 214 μm (E band) at a resolution of 19"6 to observe thermal polarized dust emission throughout the Central Molecular Zone (CMZ). DR2 consists of observations obtained in 2022 covering the region of the CMZ extending from the Brick to the Sgr C molecular clouds (corresponding to a 1° × 0°.75 region of the sky). We combine DR2 with the first FIREPLACE data release (DR1) to obtain full coverage of the CMZ (a 1°.5 × 0°.75 region of the sky). After applying total and polarized intensity significance cuts on the full FIREPLACE data set, we obtain ∼64,000 Nyquist-sampled polarization pseudovectors. The distribution of polarization pseudovectors confirms a bimodal distribution in the CMZ magnetic field orientations, recovering field components that are oriented predominantly parallel or perpendicular to the Galactic plane. This distribution of orientations is similar to what was observed in DR1 and other studies. We also inspect the magnetic fields toward a set of prominent CMZ molecular clouds (the Brick, Three Little Pigs, 50 and 20 km s −1 clouds, circumnuclear disk, CO 0.02-0.02, and Sgr C), revealing spatially varying magnetic fields having orientations that generally trace the total intensity morphologies of the clouds. We find evidence that compression from stellar winds and shear from tidal forces are prominent mechanisms influencing the structure of the magnetic fields.

Molecular clouds↗
NASA NTRS2014

Nonuniform Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3

We report measurements of the X-ray expansion of the youngest Galactic supernova remnant, G1.9+0.3, using Chandra observations in 2007, 2009, and 2011. The measured rates strongly deviate from uniform expansion, decreasing radially by about 60 along the X-ray bright SE-NW axis from 0.84 plus or minus 0.06% yr(exp -1) to 0.52% plus or minus 0.03 yr(exp -1). This corresponds to undecelerated ages of 120-190 yr, confirming the young age of G1.9+0.3 and implying a significant deceleration of the blast wave. The synchrotron-dominated X-ray emission brightens at a rate of 1.9% plus or minus 0.4% yr(exp -1). We identify bright outer and inner rims with the blast wave and reverse shock, respectively. Sharp density gradients in either the ejecta or ambient medium are required to produce the sudden deceleration of the reverse shock or the blast wave implied by the large spread in expansion ages. The blast wave could have been decelerated recently by an encounter with a modest density discontinuity in the ambient medium, such as may be found at a wind termination shock, requiring strong mass loss in the progenitor.

NONUNIFORM EXPANSION↗
NASA NTRS1995

The anomalous nuclear component in the three-dimensional heliosphere

The anomalous nuclear component is neither of solar nor galactic cosmic ray origin. Its presence in the heliosphere is an independent probe for both interplanetary electrodynamical investigations--especially solar modulation--and probably the most direct means for determining the elemental and isotopic composition of those neutral atoms in the local interstellar medium that have high first ionization potentials (e.g., He, N, O, Ne, Ar, etc.). This report is a brief account of the evolution of our knowledge of this component for readers not specializing in the subject. Included are the initial discoveries of the component, its composition, spectra, heliospheric radial and latitudinal intensity gradients, modulation over the approximately 22 year solar magnetic cycle, trapping in the magnetosphere and its use for estimating the location of a heliospheric termination shock. Recent measurements from the ULYSSES spacecraft have provided conclusive evidence that incoming neutral atoms, after photoionization by solar uv, are picked up by the solar wind, thus lending support for the concept that after their acceleration--probably at a termination shock--they return to the inner heliosphere as pseudo-cosmic rays. ULYSSES spacecraft investigations extending to approximately 56 deg south latitude reveal, for both the anomalous nuclear component and the galactic cosmic rays, that there is a surprisingly small latitudinal intensity gradient. Thus, for the current phase of the solar cycle, modulation is much more spherically symmetric in the inner solar system than had generally been believed. A further surprise is the continual presence of approximately 26 day recurrent modulation at hight latitudes, without corresponding magnetic field compressions. These results are changing our ideas and requiring modification of our models for solar modulation in three dimensions.

Simpson, J. A.↗
NASA NTRS1993

Steady state and dynamical structure of a cosmic-ray-modified termination shock

A hydrodynamic model is developed for the structure of a cosmic-ray-modified termination shock. The model is based on the two-fluid equations of diffuse shock acceleration (Drury and Volk, 1981). Both the steady state structure of the shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rates, it is shown that the natural state of the termination shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium termination shock model is shown to result in some unusual downstream structure, including transmitted shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary shocks, etc.) could induce the termination shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving shock whose structure and dynamic properties are strongly influence by the mediation of interstellar and anomalous cosmic rays.

Donohue, D. J.↗
NASA NTRS1981

Effects of drift on the transport of cosmic rays. IV - Modulation by a wavy interplanetary current sheet

The effect of a wavy interplanetary current sheet on the solar modulation of galactic cosmic rays is studied. A simple model of the heliospheric magnetic field is employed in which there is an Archimedean spiral magnetic field directed in one direction above the current sheet and another direction below. The current sheet itself is taken to be the extension by the solar wind of a surface that, at the sun, is a plane inclined at an angle alpha to the solar equator. Two magnetic sectors will therefore be seen by an observer within an angle alpha of the heliographic equator. A simple approximate model is used to investigate modulation. As the tilt angle alpha is increased from zero, it is found that the cosmic-ray intensity decreases. For reasonable variation of alpha from approximately 10 deg to approximately 30 deg, the change in intensity can be compared to that observed as one goes from solar minimum to solar maximum. It is concluded that changes in the waviness of the interplanetary current sheet can have an important, and perhaps dominant, effect in producing solar modulation of galactic cosmic rays.

Jokipii, J. R.↗
NASA NTRS1980

The evolution of supernova remnants in different galactic environments, and its effects on supernova statistics

Examination of the interaction between supernova (SN) ejecta and the various environments in which the explosive event might occur shows that only a small fraction of the many SNs produce observable supernova remnants (SNRs). This fraction, which is found to depend weakly upon the lower mass limit of the SN progenitors, and more strongly on the specfic characteristics of the associated interstellar medium, decreases from approximately 15 percent near the galctic center to 10 percent at Rgal approximately 10 kpc and drops nearly to zero for Rgal 15 kpc. Generally, whether a SNR is detectable is determined by the density of the ambient interstellar medium in which it is embeeede. The presence of large, low density cavities arpund stellar associations due to the combined effects of stellar winds and supernova shells strongly suggests that a large portion of the detectable SNRs have runway stars as their progenitors. These results explain the differences between the substantially larger SN rates in the galaxy derived both from pulsar statistics and from observations of SN events in external galaxies, when compared to the substantially smaller SN rates derived form galactic SNR statistics.

Kafatos, M.↗
NASA NTRS2021

Quantifying Feedback from Narrow Line Region Outflows in Nearby Active Galaxies. III. Results for the Seyfert 2 Galaxies Markarian 3, Markarian 78, and NGC 1068

Outflows of ionized gas driven by active galactic nuclei (AGN) may significantly impact the evolution of their host galaxies. However, determining the energetics of these outflows is difficult with spatially unresolved observations that are subject to strong global selection effects. We present part of an ongoing study using Hubble Space Telescope and Apache Point Observatory spectroscopy and imaging to derive spatially resolved mass outflow rates and energetics for narrow-line region outflows in nearby AGN that are based on multi-component photoionization models to account for spatial variations in gas ionization, density, abundances, and dust content. This expanded analysis adds Mrk 3, Mrk 78, and NGC 1068, doubling our earlier sample. We find that the outflows contain total ionized gas masses of M ≈ 10(exp 5.5)-10(exp 7.5) M⨀ and reach peak velocities of v ≈ 800-2000 km s(exp -1). The outflows reach maximum mass outflow rates of M(sub OUT) ≈ 3-12 M⨀ yr(exp -1) and encompass total kinetic energies of E ≈ 10(exp 54)-10(exp 56) erg. The outflows extend to radial distances of r ≈ 0.1-3 kpc from the nucleus, with the gas masses, outflow energetics, and radial extents positively correlated with AGN luminosity. The outflow rates are consistent with in situ ionization and acceleration where gas is radiatively driven at multiple radii. These radial variations indicate that spatially resolved observations are essential for localizing AGN feedback and determining the most accurate outflow parameters.

Active galaxies↗
NASA NTRS1990

One-dimensional cloud fluid model for propagating star formation

The aim of this project was to study the propagation of star formation (SF) with a self-consistent deterministic model for the interstellar gas. The questions of under what conditions does star formation propagate in this model and what are the mechanisms of the propagation are explored. Here, researchers used the deterministic Oort-type cloud fluid model of Scalo and Struck-Marcell (1984, also see the review of Struck-Marcell, Scalo and Appleton 1987). This cloud fluid approach includes simple models for the effects of cloud collisional coalescence or disruption, collisional energy dissipation, and cloud disruption and acceleration as the result of young star winds, HII regions and supernovae. An extensive one-zone parameter study is presented in Struck-Marcell and Scalo (1987). To answer the questions above, researchers carried out one-dimensional calculations for an annulus within a galactic disk, like the so-called solar neighborhood of the galactic chemical evolution. In the calculations the left-hand boundary is set equal to the right hand boundary. The calculation is obviously idealized; however, it is computationally convenient to study the first order effects of propagating star formation. The annulus was treated as if it were at rest, i.e., in the local rotating frame. This assumption may remove some interesting effects of a supersonic gas flow, but was necessary to maintain a numerical stability in the annulus. The results on the one-dimensional propagation of SF in the Oort cloud fluid model follow: (1) SF is propagated by means of hydrodynamic waves, which can be generated by external forces or by the pressure generated by local bursts. SF is not effectively propagated via diffusion or variation in cloud interaction rates without corresponding density and velocity changes. (2) The propagation and long-range effects of SF depend on how close the gas density is to the critical threshold value, i.e., on the susceptibility of the medium.

Titus, Timothy N.↗
NASA NTRS2003

Chandra Observation of the X-ray Source Population of NGC 6946

We present the results of a study of discrete X-ray sources in NGC 6946 using a deep Chandra ACIS observation. Based on the slope of the log N-log S distribution and the general correlation of sources with the spiral arms, we infer that the overall discrete source sample in NGC 6946 is dominated by high mass X-ray binaries, in contrast to the source distributions in M31 and the Milky Way. This is consistent with the higher star formation rate in NGC 6946 than in those galaxies. We find that the strong X-ray sources in the region of the galactic center do not correlate in detail with images of the region in the near-IR, although one of them may be coincident with the galactic center. The non-central ultra-luminous X-ray source in NGC 6946, previously identified with a supernova remnant, has an X-ray spectrum and luminosity that is inconsistent with either a traditional pulsar wind nebula or a blast wave remnant.

Holt, S. S.↗
NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 1

Contents include the following: Observations with Near Infrared Spectrometer for Hayabusa Mission in the Cruising Phase. First Results of Quadrantid Meteor Spectrum. Compositional Investigation of Binary Near-Earth Asteroid 66063 (1998 RO1): A Potentially Undifferentiated Assemblage. Impact-induced Hydrothermal Activity on Early Mars. HRTEM and EFTEM Studies of Phyllosilicate-Organic Matter Associations in Matrix and Dark Inclusions in the EET92042 CR2 Carbonaceous Chondrite. Volumetric Analysis of Martian Rampart Craters. High Pressure Melting of H-Chondrite: A Match for the Martian Basalt Source Mantle. MERView: A New Computer Program for Easy Display of MER-acquired M ssbauer Data. Distribution, Exchange, and Topographic Control of Subsurface Ice on Mars. Shock-induced Damage Beneath Normal and Oblique Impact Craters. Amphitrites Patera Studied from the Mars Express HRSC Data. Oxygen Isotope Microanalysis of Enveloping Compound Chondrules in CV3 and LL3 Chondrites. Gamma-Ray Irradiation in the Early Solar System and the Conundrum of the Lu-176 Decay Constant. Magnesium Isotope Mapping of Silica-rich Grains Having. Extreme Oxygen Isotope Anomalies Extreme Oxygen Isotopic Anomalies from Irradiation in the Early Solar System, Re-Examining the Role of Chondrules in Producing the Elemental Fractionations in Chondrites. Meteorite Data on the Solar Modulation of Galactic Cosmic Rays and an Inference on the Solar Activity Influence on Climate of the Earth. Volatiles Enrichments and Composition of Jupiter. Thinking Like a Wildcatter Prospecting for Methane in Arabia Terra, Mars. Size Distribution of Genesis Solar Wind Array Collector Fragments. Initial Subdivision of Genesis Early Science Polished Aluminum Collector. Presolar Graphite and Its Noble Gases. Young Pb-Isotopic Ages of Chondrules in CB Carbonaceous Chondrites. Fe Isotopic Composition of Martian Meteorites. Petrology and Geochemistry of Nakhlite MIL 03346: A New Martian Meteorite from Antarctica.

Source record↗
NASA NTRS2016

Astrophysical Implications of the Binary Black Hole Merger GW150914

The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that in spiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively heavy BHs (> or approx. 25 Stellar Mass) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 12 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (> or approx. 1/cu Gpc/yr) from both types of formation models. The low measured redshift (z approx. = 0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.

stars↗
NASA NTRS1979

Low luminosity galactic X-ray sources

The number of low luminosity sources found in the Galaxy has increased from a few to more than two dozen in the past three years. The sources range from isolated hot white dwarfs (HZ43) to normal stellar coronae (alpha Cen), very active coronal stars (RS CVn), flare stars (UV Ceti), interacting winds and stellar surfaces (Algol), and finally to accretion onto white dwarfs (AM Her, steady; U Gem, impulsive). The following review discusses each of these classes in some detail and portrays the wide variety of physical phenomena leading to X-ray emission.

Garmire, G. P.↗
NASA NTRS1992

Intensity variations in the interplanetary magnetic field measured by Voyager 2 and the 11-year solar cycle modulation of galactic cosmic rays

New evidence is presented to support the hypothesis that the 11-yr solar cycle modulation of galactic cosmic rays is caused by strong diffusion inside long-lived merged interaction regions. To test this hypothesis, the 1D force-field approximation of the cosmic ray modulation equation is solved. It is assumed that a constant solar wind speed convects magnetic field compressions and rarefactions unchanged through a model heliosphere. The result is a reasonable simulation of the integrated high-energy cosmic ray intensity profile from about 1982 to mid-1989. This period encompasses both the full recovery portion of the last profile from about 1982 to mid-1989. This model responds to the Voyager 2 magnetic field data by correctly timing the beginning of the new modulation cycle in late 1987. It is concluded that the present hypothesis is consistent with the results of this simulation.

Perko, J. S.↗
NASA NTRS2008

Exploring Cosmic X-ray Source Polarization

Cosmic X-ray sources are expected to be polarized, either because of their asymmetry and the role of scattering in their emission or the role of magnetic fields. Polarization at other wavelengths has been useful. X-ray polarization will provide a new handle on black hole parameters, in particular the spin, on accretion flows and outflows, on neutron star spin orientations and emission mechanisms, on the quantum mechanical effects of super-strong magnetic fields of magnetars, and on the structure of supernovae shocks. The proposed Gravity and Extreme Magnetism SMEX (GEMS) will use high efficiency polarimeters behind thin foil mirrors. The statistical sensitivity and control of systematics will allow measurement of polarization fractions as small as 1% from many galactic and extragalactic sources. Targets which should be polarized at the level that GEMS can easily measure include stellar black holes, Seyfert galaxies and quasars, blazars, rotation-powered and accretion-powered pulsars, magnetars, shell supernova remnants and pulsar wind nebulae. The polarimeters are Time Projection Chambers that allow reconstruction of images of photoelectron tracks for 2-10 keV Xrays. They can be deep without sacrificing modulation. These polarimeters do not image the sky, but the telescope point spread function and detector collimation allow structure to be resolved at the 10 arcmin level. Rotation of the spacecraft is not needed for the signal measurement in the Time Projection Chambers, but provides for measurement and correction of systematic errors. It also allows a small Bragg reflection soft X-ray experiment to be included that can be used for isolated neutron stars and blazars.

Swank, Jean Hebb↗
NASA NTRS1987

The magnetospheres of Jupiter, Saturn, and Uranus

The results published by U.S. scientists during 1983-1986 from studies related to the magnetospheres of Jupiter, Saturn, and Uranus are discussed. Consideration is given to the magnetic fields of these planets, charged particle environments, the interactions between the planetary rings and planetary satellites, the solar wind interactions, radio emissions, and auroras. Special attention is given to observations of (1) a small flux of energetic electrons and protons in the otherwise radiation-free environment in the magnetosphere under the rings of Saturn (interpreted as interactions of Galactic cosmic rays with the rings), (2) spokes, and (3) Saturn ring erosion.

Connerney, J. E. P.↗