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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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

A NEW TYPE OF COMPACT STELLAR POPULATION: DARK STAR CLUSTERS

Among the most explored directions in the study of dense stellar systems is the investigation of the effects of the retention of supernova remnants, especially that of the massive stellar remnant black holes (BHs), in star clusters. By virtue of their eventual high central concentration, these stellar mass BHs potentially invoke a wide variety of physical phenomena, the most important ones being emission of gravitational waves (GWs), formation of X-ray binaries, and modification of the dynamical evolution of the cluster. Here we propose, for the first time, that rapid removal of stars from the outer parts of a cluster by the strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster, which appears as a star cluster that is gravitationally bound by an invisible mass. We study the formation and properties of such systems through direct N-body computations and estimate that they can be present in significant numbers in the inner region of the Milky Way. We call such objects 'dark star clusters' (DSCs) as they appear dimmer than normal star clusters of similar mass and they comprise a predicted, new class of entities. The finding of DSCs will robustly cross-check BH retention; they will not only constrain the uncertain natal kicks of BHs, thereby the widely debated theoretical models of BH formation, but will also pinpoint star clusters as potential sites for GW emission for forthcoming ground-based detectors such as the Advanced LIGO. Finally, we also discuss the relevance of DSCs for the nature of IRS 13E.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

FIRST SCIENCE RESULTS FROM SOFIA/FORCAST: THE MID-INFRARED VIEW OF THE COMPACT H II REGION W3A

The massive star-forming region W3 was observed with the faint object infrared camera for the SOFIA telescope as part of the Short Science program. The 6.4, 6.6, 7.7, 19.7, 24.2, 31.5, and 37.1 {mu}m bandpasses were used to observe the emission of polycyclic aromatic hydrocarbon (PAH) molecules, very small grains, and big grains. Optical depth and color temperature maps of W3A show that IRS2 has blown a bubble devoid of gas and dust of {approx}0.05 pc radius. It is embedded in a dusty shell of ionized gas that contributes 40% of the total 24 {mu}m emission of W3A. This dust component is mostly heated by far-ultraviolet, rather than trapped Ly{alpha} photons. This shell is itself surrounded by a thin ({approx}0.01 pc) photodissociation region where PAHs show intense emission. The infrared spectral energy distribution (SED) of three different zones located at 8'', 20'', and 25'' from IRS2 shows that the peak of the SED shifts toward longer wavelengths, when moving away from the star. Adopting the stellar radiation field for these three positions, DUSTEM model fits to these SEDs yield a dust-to-gas mass ratio in the ionized gas similar to that in the diffuse interstellar medium (ISM). However, the ratio of the IR-to-UV opacity of the dust in the ionized shell is increased by a factor of {approx_equal}3 compared to the diffuse ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DISCOVERY OF A COMPACT COMPANION TO THE HOT SUBDWARF STAR BD +37 Degree-Sign 442

We report the results of the first X-ray observation of the luminous and helium-rich O-type subdwarf BD +37 Degree-Sign 442 carried out with the XMM-Newton satellite in 2011 August. X-ray emission is detected with a flux of about 3 Multiplication-Sign 10{sup -14} erg cm{sup -2} s{sup -1} (0.2-1 keV) and a very soft spectrum, well fit by the sum of a blackbody with temperature kT{sub BB} = 45{sup +11}{sub -9} eV, and a power law with a poorly constrained photon index. Significant pulsations with a period of 19.2 s are detected, indicating that the X-ray emission originates in a white dwarf or neutron star companion, most likely powered by accretion from the wind of BD +37 Degree-Sign 442.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DC CIRCUIT POWERED BY ORBITAL MOTION: MAGNETIC INTERACTIONS IN COMPACT OBJECT BINARIES AND EXOPLANETARY SYSTEMS

The unipolar induction DC circuit model, originally developed by Goldreich and Lynden-Bell for the Jupiter-Io system, has been applied to different types of binary systems in recent years. We show that there exists an upper limit to the magnetic interaction torque and energy dissipation rate in such a model. This arises because when the resistance of the circuit is too small, the large current flow severely twists the magnetic flux tube connecting the two binary components, leading to the breakdown of the circuit. Applying this limit, we find that in coalescing neutron star binaries, magnetic interactions produce negligible correction to the phase evolution of the gravitational waveform, even for magnetar-like field strengths. However, energy dissipation in the binary magnetosphere may still give rise to electromagnetic radiation prior to the final merger. For ultracompact white dwarf binaries, we find that unipolar induction does not provide adequate energy dissipation to explain the observed X-ray luminosities of several sources. For exoplanetary systems containing close-in Jupiters or super-Earths, the magnetic torque and energy dissipation induced by the orbital motion are negligible, except possibly during the early T Tauri phase, when the stellar magnetic field is stronger than 10{sup 3} G.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

NGC 1277: A MASSIVE COMPACT RELIC GALAXY IN THE NEARBY UNIVERSE

As early as 10 Gyr ago, galaxies with more than 10{sup 11} M {sub ☉} of stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (≲0.1%) may have survived untouched until today. Searches for such relic galaxies, useful windows to explore the early universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high redshift (M {sub *} ≳ 10{sup 11} M {sub ☉}; R{sub e} ≲ 1.5 kpc) have been found in the local universe, but their stars are far too young for the galaxy to be a relic galaxy. This paper explores the first case of a nearby galaxy, NGC 1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfills many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H] = 0.20 ± 0.04 with a smooth decline toward the outer regions) and α-enriched ([α/Fe] = 0.4 ± 0.1). This suggests a very short formation time scale for the bulk of the stars in this galaxy. This object also rotates very fast (V {sub rot} ∼ 300 km s{sup –1}) and has a large central velocity dispersion (σ > 300 km s{sup –1}). NGC 1277 allows the exploration in full detail of properties such as the structure, internal dynamics, metallicity, and initial mass function as they were at ∼10-12 Gyr ago when the first massive galaxies were built.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

INTERACTING QUARK MATTER EQUATION OF STATE FOR COMPACT STARS

Lattice quantum chromodynamics (QCD) studies of the thermodynamics of hot quark-gluon plasma demonstrate the importance of accounting for the interactions of quarks and gluons if one wants to investigate the phase structure of strongly interacting matter. Motivated by this observation and using state-of-the-art results from perturbative QCD, we construct a simple, effective equation of state (EOS) for cold quark matter that consistently incorporates the effects of interactions and furthermore includes a built-in estimate of the inherent systematic uncertainties. This goes beyond the MIT bag model description in a crucial way, yet leads to an EOS that is equally straightforward to use. We also demonstrate that, at moderate densities, our EOS can be made to smoothly connect to hadronic EOSs, with the two exhibiting very similar behavior near the matching region. The resulting hybrid stars are seen to have masses similar to those predicted by the purely nucleonic EOSs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

J2229+2725: an extremely low metallicity dwarf compact star-forming galaxy with an exceptionally high [O iii ]λ5007/[O ii ]λ3727 flux ratio of 53

ABSTRACT Using the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS), we have obtained optical spectroscopy of one of the most metal-poor dwarf star-forming galaxies (SFGs) in the local Universe, J2229+2725. This galaxy with a redshift z = 0.0762 was selected from the Data Release 16 of the Sloan Digital Sky Survey (SDSS). Its properties derived from the LBT observations are most extreme among SFGs in several ways. Its oxygen abundance 12 + logO/H = 7.085 ± 0.031 is among the lowest ever observed for an SFG. With its very low metallicity, an absolute magnitude Mg = −16.39 mag, a low stellar mass M⋆ = 9.1 × 106 M⊙, and a very low mass-to-light ratio M⋆/Lg ∼ 0.0166 (in solar units), J2229+2725 deviates strongly from the luminosity–metallicity relation defined by the bulk of the SFGs in the SDSS. J2229+2725 has a very high specific star formation rate sSFR ∼ 75 Gyr−1, indicating very active ongoing star formation. Three other features of J2229+2725 are most striking, being the most extreme among lowest metallicity SFGs: (1) a ratio O32 = I([O iii]λ5007)/I([O ii]λ3727) ∼ 53, (2) an equivalent width of the H β emission line EW(H β) of 577 Å, and (3) an electron number density of ∼1000 cm−3. These properties imply that the starburst in J2229+2725 is very young. Using the extremely high O32 in J2229+2725, we have improved the strong-line calibration for the determination of oxygen abundances in the most metal-deficient galaxies, in the range 12 + logO/H $\lesssim$ 7.3.

Izotov, Y. I.↗
DOE OSTI2023

Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae

ABSTRACT We perform a comparative analysis of nucleosynthesis yields from binary neutron star (BNS) mergers, black hole-neutron star (BHNS) mergers, and core-collapse supernovae (CCSNe) with the goal of determining which are the most dominant sources of r-process enrichment observed in stars. We find that BNS and BHNS binaries may eject similar mass distributions of robust r-process nuclei post-merger (up to third peak and actinides, A ∼ 200−240), after accounting for the volumetric event rates. Magnetorotational (MR) CCSNe likely undergo a weak r-process (up to A ∼ 140) and contribute to the production of light element primary process (LEPP) nuclei, whereas typical thermal, neutrino-driven CCSNe only synthesize up to first r-process peak nuclei (A ∼ 80−90). We also find that the upper limit to the rate of MR CCSNe is $\lesssim 1~{{\ \rm per\ cent}}$ the rate of typical thermal CCSNe; if the rate was higher, then weak r-process nuclei would be overproduced. Although the largest uncertainty is from the volumetric event rate, the prospects are encouraging for confirming these rates in the next few years with upcoming surveys. Using a simple model to estimate the resulting kilonova light curve from mergers and our set of fiducial merger parameters, we predict that ∼7 BNS and ∼2 BHNS events will be detectable per year by the Vera C. Rubin Observatory (LSST), with prior gravitational wave (GW) triggers.

Astronomy & Astrophysics↗
DOE OSTI2011

Entanglement and separability of two-qubit states on Minkowski space with compact support

The entanglement properties of a two-qubit system are analyzed from the point of view of Lie algebras and geometry. We deal with 4x4 matrices belonging to a particular class having seven free parameters, constructed from the imposed symmetries on two-qubit states expanded in terms of a basis whose elements belong to a subalgebra of su(4). The entanglement or separability character of the state is determined and measured by analyzing the eigenvalues of an auxiliary matrix obtained from the original state after performing on it a nonunitary operation. In terms of its eigenvalues, we define two squared distances having a Minkowski metric, s{sup 2}=t{sup 2}-V(vector sign){sup 2}, which become a measure of the entanglement. The Minkowski metric is a signature of that class of two-qubit states (matrices) and also of the auxiliary matrices to be constructed. The squared distance is invariant by any unitary transformation on the two-qubit state. We illustrate the theory with examples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗