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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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NASA NTRS1993

Successive X-ray bursts from accreting neutron stars

The evolution of a neutron star undergoing a series of thermonuclear flashes in its accreted hydrogen-rich layer has been numerically followed to determine the effects of the history of the neutron star's thermal and compositional structure on the properties of the emitted X-ray bursts. Burst characteristics are studied for a range of mass accretion rates, CNO abundances in the accreted matter, and initial thermal states of the underlying neutron star core; the bursts exhibit erratic behavior for low CNO metal abundances and cool neutron star cores, with the burst recurrence time scales varying by 1-2 orders of magnitude. There is typically a continued presence of a substantial amount of unburnt hydrogen in the accreted layer throughout the series of the X-ray burst events. Convective mixing during the quiescent phase leads to the inward transport of helium to high densities and eventually to the initiation of the next outburst. The resulting bursts can be weak and, in such cases, are characterized by short recurrence time scales (1-2 hr), low peak luminosities (0.1-0.2 times the Eddington value), and low alpha-values (about 20).

Taam, Ronald E.↗

NASA NTRS1984

Protostellar formation in rotating interstellar clouds. IV Nonisothermal collapse

Radiative transfer in the Eddington approximation is included in a multidimensional, self-gravitational, hydrodynamical computer code. Details of the numerical solution and thermodynamic relations are given. Comparison calculations with previous spherically symmetrical models of protostellar collapse are used to validate the basic approach and the artifices which allow the explicit hydrodynamics code to follow the accretion of gas onto a quasi-equilibrium core. A series of axisymmetric models is used to investigate the importance of rotation in collapsing clouds, as the initial amount of angular momentum is lowered, with an emphasis on the possible formation of rings. Rings readily form even in the nonisothermal regime except for very low initial angular momenta; even these clouds may experience ring formation prior to reaching stellar densities. The models imply that other effects (such as gravitational torques or turbulent viscosity) may be necesary to avoid binary formation and thus result in a presolar nebula consistent with the assumptions of either Safronov or Cameron.

Boss, A. P.↗

NASA NTRS1983

Prebiotic organic syntheses and the origin of life

The outline of a modern paradigm for the origins of life on earth was first formulated by Oparin (1924). According to the considered hypothesis, living organisms arose naturally on the primitive earth through a lengthy process of chemical evolution of organic matter which began in the atmosphere and culminated in the primordial seas. Details regarding the chemical evolution paradigm are discussed, and chemical evolutionary processes formulated by principal contributors are reviewed in a historical context. Attention is given to the Oparin model of the prebiotic earth, the Urey model, the Rubey model, a multistage model for early atmospheric evolution, and other variations on the theme of prebiotic atmospheres. Evidence in support of the chemical evolution paradigm is considered along with modern models regarding the accretion of earth and the formation of its core, and problems and prospects for future studies.

Chang, S.↗

NASA NTRS1993

Evolutionary history of the mesosiderite asteroid - A chronologic and petrologic synthesis

The evolutionary history of the mesosiderite parent body is composed of six principal epochs. (1) Accretion occurred about 4.56 Ga ago, and (2) initial melting occurred less than about 26 Ma after accretion. (3) Significant crustal remelting occurred more than 4.47 Ga ago, possibly during metal-silicate mixing caused by the accretion of a large metallic Fe-Ni core fragment with some overlying mantle to the MPB regolith. (4) Localized impact melting 4.5-3.9 Ga ago produced quench-textured clasts and caused mesosiderite metamorphism and the extensive melting of type-4 mesosiderites. (5) Collisional disruption and gravitational reassembly occurred about 3.9 Ga ago, causing extensive degassing of Ar and resetting the metallographic cooling rates to about 1 C/Ma. (6) Impact excavitation and ejection of deeply buried breccias occurred much less than 3.9 Ga.

Rubin, Alan E.↗

NASA NTRS1993

Origin and thermal evolution of Mars

The thermal evolution of Mars is governed by subsolidus mantle convection beneath a thick lithosphere. Models of the interior evolution are developed by parameterizing mantle convective heat transport in terms of mantle viscosity, the superadiabatic temperature rise across the mantle and mantle heat production. Geological, geophysical, and geochemical observations of the composition and structure of the interior and of the timing of major events in Martian evolution, such as global differentiation, atmospheric outgassing and the formation of the hemispherical dichotomy and Tharsis, are used to constrain the model computations. Isotope systematics of SNC meteorites suggest core formation essentially contemporaneously with the completion of accretion. Other aspects of this investigation are discussed.

Schubert, G.↗

NASA NTRS2007

Quasar Astrophysics with the Space Interferometry Mission

Optical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V = 19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.

instrumentation↗

NASA NTRS1980

Recent depositional history of Apollo 16 and 17 cores

Measurements of Al-26 and Mn-53 in the Apollo 17 drive tube 76001 show a clear integral excess of activity above expected production down to a depth of at least 9 gm/sq cm. This excess is interpreted as a continuous accretion of highly irradiated surface material slowly transported downslope by impact or other processes at a buildup rate of 1.5 cm/m.y. This drive tube, 76001, was collected near a change in slope on the North Massif. Integral excesses have also been observed in other Apollo 16 and 17 cores. Evidence in the Al-26 and Mn-53 record for continuous accretion is shown for Apollo 16 cores 60007 and 60010 and the Apollo 16 deep drill string 70009-70001. This evaluation shows that accretion at specific sites, either through continuous downslope movement or regolith material on the moon, or simply through small impact redistribution, is common on both small and large scales.

Evans, J. C.↗

NASA NTRS1989

On the rapid formation of giant planet cores

The formation of the ice-rock cores of the giant planets by density wave-assisted accretion is outlined. The process could be rapid (100,000-1,000,000 yr) and completed within the probable lifetime of the solar nebula. The mechanism works for both Jupiter and Saturn and does not require a large excess of mass over that believed present in their cores.

Ward, William R.↗

NASA NTRS1990

The radio properties of cD galaxies in Abell clusters. I - An X-ray selected sample

The radio and X-ray properties of a sample of 27 cD galaxies in rich clusters are presented. The radio data consist of 6 cm VLA maps at a resolution of 1-2 arcsec. The X-ray data consist of images and surface-brightness profiles from the Einstein IPC and derived quantities such as cooling times, mass-accretion rates, and thermal pressures from Arnaud (1988). These data are used to explore the relationship between X-ray cooling cores, and the power and morphology of the radio emission. It is found that 71 percent of the cD's with X-ray cooling cores are radio loud, whereas a smaller but still significant 23 percent of cD's without cooling cores are detected at 6 cm above 0.2 mJy. Among the radio galaxies in noncooling core clusters are luminous and extended wide-angle tails. There is a weak correlation between the mass-accretion rate and the radio power for cD's. There is also an interesting class of cooling core cluster (e.g., A2052) with small diameter, amorphous radio emission that may be the result of diffusion along radial magnetic fields set up in cooling inflows. Finally, the relationships between optical emission-line luminosity with radio power and mass-accretion rate are examined.

Burns, Jack O.↗

NASA NTRS2019

Analysis of Experimental Ice Accretion Data and Assessment of a Thermodynamic Model During Ice Crystal Icing

This paper evaluates a thermodynamic ice crystal icing model that has been previously presented to describe the possible mechanisms of icing within the core of a turbofan jet engine. The model functions between two distinct ice accretions based on a surface energy balance: freeze-dominated icing and melt-dominated icing. Freeze-dominated icing occurs when liquid water (from melted ice crystals) freezes and accretes on a surface along with the existing ice of the impinging water and ice mass. This freeze-dominated icing is characterized as having strong adhesion to the surface. The amount of ice accretion is partially dictated by a freeze fraction, which is the fraction of impinging liquid water that freezes. Melt-dominated icing occurs as unmelted ice on a surface accumulates. This melt-dominated icing is characterized by weakly bonded surface adhesion. The amount of ice accumulation is partially dictated by a melt fraction, which is the fraction of impinging ice crystals that melts. Experimentally observed ice growth rates suggest that only a small fraction of the impinging ice remains on the surface, implying a mass loss mechanism such as splash, runback, bounce, or erosion. The fraction of mass loss must be determined in conjunction with the fraction of freezing liquid water or fraction of melting ice on an icing surface for a given ice growth rate. This mass loss parameter, however, along with the freeze fraction and melt fraction, are the only experimental parameters that are currently not measured directly. Using icing growth rates from ice crystal icing experiments, a methodology that has been previously proposed is used to determine these unknown parameters. This work takes ice accretion data from tests conducted by the National Aeronautics and Space Administration (NASA) at the Glenn Research Center in 2018 that examined the fundamental physics of ice crystal icing. This paper continues evaluation of the thermodynamic model from a previous effort, with additions to the model that account for sub-freezing temperatures that have been observed at the leading edge of the airfoil during icing. The predicted temperatures were generally in good agreement with measured temperatures. Other key findings include the total wet-bulb temperature being a good first order indicator of whether icing is freeze-dominated (sub-freezing values) or melt-dominated (above freezing). Maximum sticking efficiency values, the fraction of impinging mass that adheres to a surface, was calculated to be about 0.2, and retained this maximum value for a range of melt ratios (0.3 to 0.65 and possibly higher), which is defined as the ratio of liquid water content to total water content. Higher air velocities reduced the maximum sticking efficiency and shifted the icing regime to higher melt ratio values. Finally, the leading edge ice accretion angle was found to be related to ice growth (lower growth rates for smaller angles) and melt ratio (smaller melt ratios resulted in smaller angles, likely due to erosion effects).

Ice-Crystal Icing↗

NASA NTRS1989

Active galactic nuclei. III - Accretion flow in an externally supplied cluster of black holes

This third paper in the series modeling QSOs and AGNs as clusters of accreting black holes studies the accretion flow within an externally supplied cluster. Significant radiation will be emitted by the cluster core, but the black holes in the outer halo, where the flow is considered spherically symmetric, will not contribute much to the overall luminosity of the source because of their large velocities relative to the infalling gas and therefore their small accretion radii. As a result, the scenario discussed in Paper I will refer to the cluster cores, rather than to entire clusters. This will steepen the high-frequency region of the spectrum unless inverse Compton scattering is effective. In many cases accretion flow in the central part of the cluster will be optically thick to electron scattering, resulting in a spectrum featuring optically thick radiative component in addition to power-law regimes. The fitting of these spectra to QSO and AGN observations is discussed, and application to 3C 273 is worked out as an example.

Pacholczyk, A. G.↗

NASA NTRS1985

Thermal, dynamic and compositional aspects of the core-forming Earth

Core formation is the most important and singular differentiation event in the history of a terrestrial planet. It almost certainly involved the downward migration of a partially or wholly molten iron alloy through a silicate and oxide mantle, and was contemporaneous with accretion. Several important, unresolved issues which have implications for mantle and core geochemistry, the thermal history of the Earth, and the origin of geomagnetism are addressed: whether the early Earth was molten; whether core formation involved low or high pressure geochemistry, or both; early Earth mantle homogenization; whether equilibration established between core forming material and the mantle through which it migrated; and how much iron is stranded and unable to reach the core.

Stevenson, D. J.↗

NASA NTRS2018

Evaluation of a Thermodynamic Ice Crystal Icing Model Using Experimental Ice Accretion Data

This paper presents the evaluation of a thermodynamic ice crystal icing model, previously presented to describe the possible mechanisms of icing within the core of a turbofan jet engine. It has been proposed that there are two types of distinct ice accretions based on a surface energy balance: freeze-dominated icing and melt-dominated icing. In the former, ice accretion occurs where a freeze fraction (0 to 1) of melted ice crystals freezes on a surface, along with the existing ice of the impinging water and ice mass. This freeze-dominated icing is characterized by having strong adhesion to the surface. In the latter, icing occurs from accumulated unmelted ice on a surface, where a melt fraction (0 to 1) dictates the amount of unmelted impinged ice. This melt-dominated icing is characterized by weakly bonded surface adhesion. The experimentally observed ice growth rates suggest that only a small fraction of the impinging ice remains on the surface, implying a mass loss mechanism such as splash, runback, bounce, or erosion. This mass loss parameter must be determined in conjunction with the fraction of freezing liquid water or fraction of melting ice on an icing surface. This loss parameter, however, along with the freeze and melt fraction, are the only experimental parameters that are currently not measured directly. Using reported icing growth rates from published ice crystal icing experiments, a methodology is proposed to determine these unknown parameters. This work takes reported ice accretion data from tests conducted by the National Aeronautics and Space Administration (NASA) in 2016 and tests NASA collaborated on with the National Research Council (NRC) of Canada in 2012 that examined the fundamental physics of ice crystal icing. Those research efforts sought to generate icing conditions representative of those that occur inside a jet engine when ingesting ice crystals. This paper presents the fundamental equations of the thermodynamic model, the methodology used to determine the aforementioned unknown icing parameters, and results from model evaluation using experimental data. In addition, this paper builds on the previously proposed model by adding a transient conduction term to explain ice growth behavior at the onset of experimental tests that was observed to be different from steady-state ice growth that occurred later in the test run.With the addition of this energy term, this becomes a quasi-steady model. A key finding from this work suggests that mass loss fractions can exceed 0.90 for steady ice growth periods. In addition, due to conductive heat fluxes when using a warmer-than-freezing airfoil, lower mass loss fraction values were calculated during the initial transient period.

Ice-Crystal Ice Accretion↗

NASA NTRS2002

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

Greene, Thomas P.↗

NASA NTRS1989

Radio emission and the hot interstellar medium of early-type galaxies

The results of an analysis of a sample of 84 elliptical and S0 galaxies, observed in X-rays with the Einstein Observatory and in radio continuum at 5 GHz, are reported. Radio flux densities result in some of the lowest radio powers yet reported for early-type galaxies. Radio structures extending beyond the optical radius are found only in galaxies with 5 GHz radio power greater than about 10 exp 29.5 ergs/s/Hz. Radio and X-ray luminosities are correlated, although with large intrinsic scatter, suggesting that more than one mechanism may be involved. A correlation between core radio power and the X-ray-to-optical ratio suggests a connection between the hot ISM and nuclear radio sources and points to accreting cooling flows as the fuel for the radio sources. For the same radio core power, extended radio lobes tend to be associated with galaxies with relatively smaller X-ray-to-optical ratios, pointing to the importance of the hot ISM in disrupting the radio jets and confining extended radio structures.

Fabbiano, G.↗

NASA NTRS1997

The First Few Parsecs of the Jets in NGC-4261

We have imaged the nucleus of the nearby radio galaxy NGC 4261 (3C270) with the VLBA at 1.6, 8.4, 22, and 43 GHz. At 8.4 GHz our image reveals a narrow gap in emission just east of the core, which we interpret as absorption by an inner accretion disk seen nearly edge-on. If correct, this interpretation implies that the radio jets are almost perpendicular to our line of sight. Thus, NGC 4261 provides an unusually good opportunity to measure component proper motions in both jet and counterjet, free from most relativistic beaming effects. Observations to do this are underway. This is one of the very few sources in which both jet and counterjet are detectable on parsec scales, and it is also one of the closest "classical" double-lobed radio galaxies. Consequently, NGC 4261 is a good laboratory for testing models of jets in low luminosity radio galaxies.

Jones, Dayton↗

NASA NTRS1999

The First Few Parsecs of the Jets in NGC 4261

interferometry↗

NASA NTRS1972

The origin and chemical composition of the earth's core

The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

Murthy, V. R.↗