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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Spectroscopic confirmation of an ultramassive and compact galaxy at z = 3.35: A detailed look at an early progenitor of local giant ellipticals

We present the first spectroscopic confirmation of an ultramassive galaxy at redshift z>3 using data from Keck-NIRSPEC, VLT-X-shooter, and GTC-Osiris. We detect strong [O iii] and Lyα emission, and weak [O ii], C iv, and He ii, placing C1-23152 at a spectroscopic redshift of z{sub spec}=3.351. The modeling of the emission-line-corrected spectral energy distribution (SED) results in a best-fit stellar mass of M{sub ∗}=3.1{sub −0.7}{sup +0.6}×10{sup 11} M{sub ⊙}, a star formation rate of <7 M{sub ⊙} yr{sup −1}, and negligible dust extinction. The stars appear to have formed in a short intense burst ∼300–500 Myr prior to the observation epoch, setting the formation redshift of this galaxy at z ∼ 4.1. From the analysis of the line ratios and widths and the observed flux at 24 μm, we confirm the presence of a luminous hidden active galactic nucleus (AGN), with bolometric luminosity of ∼10{sup 46} erg s{sup −1}. Potential contamination of the observed SED from the AGN continuum is constrained, placing a lower limit on the stellar mass of 2×10{sup 11} M{sub ⊙}. HST/WFC3 H{sub 160} and ACS I{sub 814} images are modeled, resulting in an effective radius of r{sub e}∼1 kpc in the H{sub 160} band and a Sérsic index n∼4.4. This object may be a prototype of the progenitors of local most massive elliptical galaxies in the first 2 Gyr of cosmic history, having formed most of its stars at z>4 in a highly dissipative, intense, and short burst of star formation. C1-23152 is completing its transition to a post-starburst phase while hosting a powerful AGN, potentially responsible for the quenching of the star formation activity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A consistent picture emerges: A compact X-ray continuum emission region in the gravitationally lensed quasar SDSS J0924+0219

We analyze the optical, UV, and X-ray microlensing variability of the lensed quasar SDSS J0924+0219 using six epochs of Chandra data in two energy bands (spanning 0.4–8.0 keV, or 1–20 keV in the quasar rest frame), 10 epochs of F275W (rest-frame 1089 Å) Hubble Space Telescope data, and high-cadence R-band (rest-frame 2770 Å) monitoring spanning 11 years. Our joint analysis provides robust constraints on the extent of the X-ray continuum emission region and the projected area of the accretion disk. The best-fit half-light radius of the soft X-ray continuum emission region is between 5×10{sup 13} and 10{sup 15} cm, and we find an upper limit of 10{sup 15} cm for the hard X-rays. The best-fit soft-band size is about 13 times smaller than the optical size, and roughly 7GM{sub BH}/c{sup 2} for a 2.8×10{sup 8} M{sub ⊙} black hole, similar to the results for other systems. We find that the UV emitting region falls in between the optical and X-ray emitting regions at 10{sup 14} cm < r{sub 1/2,UV}<3×10{sup 15} cm. Finally, the optical size is significantly larger, by 1.5σ, than the theoretical thin-disk estimate based on the observed, magnification-corrected I-band flux, suggesting a shallower temperature profile than expected for a standard disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HORIZON-SCALE LEPTON ACCELERATION IN JETS: EXPLAINING THE COMPACT RADIO EMISSION IN M87

It has now become clear that the radio jet in the giant elliptical galaxy M87 must turn on very close to the black hole. This implies the efficient acceleration of leptons within the jet at scales much smaller than feasible by the typical dissipative events usually invoked to explain jet synchrotron emission. Here we show that the stagnation surface, the separatrix between material that falls back into the black hole and material that is accelerated outward forming the jet, is a natural site of pair formation and particle acceleration. This occurs via an inverse Compton pair catastrophe driven by unscreened electric fields within the charge-starved region about the stagnation surface and substantially amplified by a post-gap cascade. For typical estimates of the jet properties in M87, we find excellent quantitive agreement between the predicted relativistic lepton densities and those required by recent high-frequency radio observations of M87. This mechanism fails to adequately fill a putative jet from Sagittarius A{sup *} with relativistic leptons, which may explain the lack of an obvious radio jet in the Galactic center. Finally, this process implies a relationship between the kinetic jet power and the gamma-ray luminosity of blazars, produced during the post-gap cascade.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE HYDRODYNAMICAL MODELS OF THE COMETARY COMPACT H ii REGION

We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M{sub ⊙} star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm{sup −3}) molecular material with a stellar velocity of 15 km s{sup −1}. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H{sub 2} S(2) lines from the ionized regions and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

The Role of Unit-Cell Topology in Modulating the Compaction Response of Additively Manufactured Cellular Materials using Simulations and Validation Experiments

Additive manufacturing has enabled a transformational ability to create cellular structures (or foams) with tailored topology. Compared to their monolithic polymer counterparts, cellular structures are potentially suitable for systems requiring materials with high specific energy-absorbing capability to provide enhanced damping. In this work, we demonstrate the utility of controlling unit-cell topology with the intent of obtaining a desired stress–strain response and energy density. Using mesoscale simulations that resolve the unit-cell sub-structures, we validate the role of unit-cell topology in selectively activating a buckling mode and thereby modulating the characteristic stress–strain response. Simulations incorporate a linear viscoelastic constitutive model and a hyperelastic model for simulating large deformation of the polymer under both tension and compression. Simulated results for nine different cellular structures are compared with experimental data to gain insights into three different modes of buckling and the corresponding stress–strain response.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A compact approach to higher-resolution resonant inelastic x-ray scattering detection using photoelectrons

The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba 2 Cu 3 O 4 Cl 2 at the Cu L 3 -edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd-excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Measuring the Kerr spin parameter of a non-Kerr compact object with the continuum-fitting and the iron line methods

Under the assumption that astrophysical black hole candidates are the Kerr black holes of general relativity, the continuum-fitting method and the analysis of the Kα iron line are today the only available techniques capable of providing a relatively reliable estimate of the spin parameter of these objects. If we relax the Kerr black hole hypothesis and we try to test the nature of black hole candidates, we find that there is a strong correlation between the measurement of the spin and possible deviations from the Kerr solution. The properties of the radiation emitted in a Kerr spacetime with spin parameter a{sub *} are indeed very similar, and practically indistinguishable, from the ones of the radiation emitted around a non-Kerr object with different spin. In this paper, I address the question whether measuring the Kerr spin with both the continuum-fitting method and the Kα iron line analysis of the same object can be used to claim the Kerr nature of the black hole candidate in the case of consistent results. In this work, I consider two non-Kerr metrics and it seems that the answer does depend on the specific background. The two techniques may either provide a very similar result (the case of the Bardeen metric) or show a discrepancy (Johannsen-Psaltis background)

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Stellar equilibrium configurations of compact stars in f ( R , T ) theory of gravity

In this article we study the hydrostatic equilibrium configuration of neutron stars and strange stars, whose fluid pressure is computed from the equations of state p =ωρ{sup 5/3} and p =0.28(ρ−4B), respectively, with ω and B being constants and ρ the energy density of the fluid. We start by deriving the hydrostatic equilibrium equation for the f ( R , T ) theory of gravity, with R and T standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Such an equation is a generalization of the one obtained from general relativity, and the latter can be retrieved for a certain limit of the theory. For the f ( R , T )= R +2λ T functional form, with λ being a constant, we find that some physical properties of the stars, such as pressure, energy density, mass and radius, are affected when λ is changed. We show that for a fixed central star energy density, the mass of neutron and strange stars can increase with λ. Concerning the star radius, it increases for neutron stars and it decreases for strange stars with the increment of λ. Thus, in f ( R , T ) theory of gravity we can push the maximum mass above the observational limits. This implies that the equation of state cannot be eliminated if the maximum mass within General Relativity lies below the limit given by observed pulsars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Confronting new NICER mass-radius measurements with phase transition in dense matter and twin compact stars

The (re)analysis of data on the X-ray emitting pulsars PSR J0030+0451 and J0740+6620, as well as new results on PSR J0437-4715 and J1231-1411, are confronted with the predictions of the equation of state (EoS) models allowing for strong first-order phase transition for the mass-radius (M-R) diagram. Here, we use models that are based on a covariant density functional (CDF) EoS for nucleonic matter at low densities and a quark matter EoS, parameterized by the speed of sound, at higher densities. To account for the variations in the ellipses for PSR J0030+0451 obtained from different analyses, we examined three scenarios to assess their consistency with our models, focusing particularly on the potential formation of twin stars. We found that in two scenarios, where the ellipses for PSR J0030+0451 and J0437-4715 with masses close to the canonical mass ∼ 1.4 M ⊙ are significantly separated, our models allow for the presence of twin stars as a natural explanation for potential differences in the radii of these stars.

X-ray binaries↗
DOE OSTI2022

Reply to Comment on ‘The advanced tokamak path to a compact net electric fusion pilot plant’

Abstract The Comment by Manheimer (submitted to Nucl. Fusion with this response) on our recent paper Buttery et al (2021 Nucl. Fusion 61 046028), has mischaracterized our paper with a series of misleading statements about its content, which it then seeks to refute. It also offers a series of assertions that are unsupported by refereed publication or scientific data—and sometimes in contradiction to the published record and well-established points in the scientific community. In this response we address the main thrusts and themes of the comment, while providing a point-by-point response in the appendix.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Design of a compact, cryogen-free superconducting solenoid for the electron lens of the Fermilab Integrable Optics Test Accelerator (IOTA)

The proposed electron lens for Fermilab's Integrable Optics Test Accelerator (IOTA) will broaden its capabilities by enabling new research in nonlinear integrable optics, space-charge compensation, proton beam cooling, and more. The electron lens is based on a 5–10 keV, 1–2 A electron beam, shaped using a 0.7 m long, 0.8 T solenoidal magnetic field. A cryogen-free superconducting solenoid has been designed to provide this solenoidal field, taking into consideration the constraints on space, utilities, and infrastructure in the IOTA experimental hall. The solenoid is made of copper stabilized niobium-titanium conductor, conduction-cooled using 4 K closed-cycle cryocoolers. This paper describes the overall design of the solenoid encompassing its mechanical construction, current leads optimization, cryogenic thermal modeling that provides estimates of cooldown time and static/dynamic heat loads, and quench analysis.

43 PARTICLE ACCELERATORS↗