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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 NTRS2011

The James Webb Space Telescope: Capabilities for Exoplanet Science

The James Webb Space Telescope (JWST) is a large aperture (6.5 meter), cryogenic space telescope with a suite of near and mid-infrared instruments covering the wavelength range of 0.6 micron to 28 micron. JWST's primary science goal is to detect and characterize the first galaxies. It will also study the assembly of galaxies, stellar and planetary system formation, and the formation and evolution of planetary systems. We will review the design of JWST, and discuss the current status of the project, with emphasis on recent progress in the construction of the observatory. We also review the capabilities of the observatory for observations of exosolar planets and debris disks by means of coronagraphic imaging, and high contrast imaging and spectroscopy. This discussion will focus on the optical and thermal performance of the observatory, and will include the current predictions for the performance of the observatory, with special reference to the demands of exoplanet science observations.

Clampin, Mark↗
NASA NTRS2012

The Extragalactic Background Light and the Gamma-ray Opacity of the Universe

The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefore plays a crucial role in cosmological tests for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe. The EBL also plays an important role in the propagation of very high energy gamma-rays which are attenuated en route to Earth by pair producing gamma-gamma interactions with the EBL and CMB. The EBL affects the spectrum of the sources, predominantly blazars, in the approx 10 GeV to 10 TeV energy regime. Knowledge of the EBL intensity and spectrum will allow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and VHE gamma-ray production models. Conversely, knowledge of the intrinsic gamma-ray spectrum and the detection of blazars at increasingly higher redshifts will set strong limits on the EBL and its evolution. This paper reviews the latest developments in the determination of the EBL and its impact on the current understanding of the origin and production mechanisms of gamma-rays in blazars, and on energy releases in the universe. The review concludes with a summary and future directions in Cherenkov Telescope Array techniques and in infrared ground-based and space observatories that will greatly improve our knowledge of the EBL and the origin and production of very high energy gamma-rays.

Dwek, Eli↗
NASA NTRS2012

Constraints on the Nature of CID-42: Recoil Kick or Supermassive Black Hole Pair?

The galaxy CXOC J100043.1+020637, also known as CID-42, is a highly unusual object. An apparent galaxy merger remnant, it displays signatures of both an inspiraling, kiloparsecscale active galactic nucleus (AGN) pair and of a recoiling AGN with a kick velocity approximately greater than 1300 km s(exp -1). Among recoiling AGN candidates, CID-42 alone has both spatial offsets (in optical and X-ray bands) and spectroscopic offsets. In order to constrain the relative likelihood of both scenarios, we develop models using hydrodynamic galaxy merger simulations coupled with radiative transfer calculations. Our gas-rich, major merger models are generally well matched to the galactic morphology and to the inferred stellar mass and star formation rate. We show that a recoiling supermassive black hole (SMBH) in CID-42 should be observable as an AGN at the time of observation. However, in order for the recoiling AGN to produce narrow-line emission, it must be observed shortly after the kick while it still inhabits a dense gaseous region, implying a large total kick velocity (vk approximately greater than 2000 km s(exp -1)). For the dual AGN scenario, an unusually large broad-line offset is required, and the best match to the observed morphology requires a galaxy that is less luminous than CID-42. Further, the lack of X-ray emission from one of the two optical nuclei is not easily attributed to an intrinsically quiescent SMBH or to a Compton-thick galactic environment. While the current data do not allow either the recoiling or the dual AGN scenario for CID-42 to be excluded, our models highlight the most relevant parameters for distinguishing these possibilities with future observations. In particular, high-quality, spatially-resolved spectra that can pinpoint the origin of the broad and narrow line features will be critical for determining the nature of this unique source.

Blecha, Laura↗
NASA NTRS2019

X-ray Binary Luminosity Function Scaling Relations for Local Galaxies Based on Subgalactic Modeling

We present new Chandra constraints on the X-ray luminosity functions(XLFs)of X-ray binary(XRB)populations, as well as their scaling relations, for a sample of 38 nearby galaxies(D = 3.4–29 Mpc). Our galaxy sample is drawn primarily from the Spitzer Infrared Nearby Galaxies Survey(SINGS)and contains a wealth of Chandra(5.8 Ms total)and multiwavelength data, allowing for star formation rates(SFRs)and stellar masses(M⁎)to be measured on subgalactic scales. We divided the 2478 X-ray-detected sources into 21 subsamples in bins of specific SFR(sSFR ≡ SFR/M⁎)and constructed XLFs. To model the XLF dependence on sSFR, we fit a global XLF model, containing contributions from high-mass XRBs(HMXBs), low-mass XRBs(LMXBs), and background sources from the cosmic X-ray background that respectively scale with SFR, M⁎, and sky area. We find an HMXB XLF that is more complex in shape than previously reported and an LMXB XLF that likely varies with sSFR, potentially due to an age dependence. When applying our global model to XLF data for each individual galaxy, we discover a few galaxy XLFs that significantly deviate from our model beyond statistical scatter. Most notably, relatively low-metallicity galaxies have an excess of HMXBs above≈10^(38)erg/s, and elliptical galaxies that have relatively rich populations of globular clusters(GCs)show excesses of LMXBs compared to the global model. Additional modeling of how the XRB XLF depends on stellar age, metallicity, and GC specific frequency is required to sufficiently characterize the XLFs of galaxies.

Bret D. Lehmer↗
NASA NTRS2024

Tracing Presolar Grain Populations Through Matrix Alteration Histories

Primitive meteorites preserve remnants of evolved stars as presolar grains, from asymptotic and red giant branch stars, novae and supernovae. These grains retain records of the formation mechanisms of the stellar environment from which they condensed, as well as physical and chemical processes in the interstellar medium (ISM), solar nebula and the parent bodies in which they are found. Consequently, their study can refine our understanding of the solar system and external stellar and planetary systems. However, presolar grains and their records can be altered, re-equilibrated with the surrounding matrix, and eventually lost through aqueous and thermal processing on the meteorite parent body. NanoSIMS is the most rapid and effective method for in situ identification of presolar grains via their highly anomalous isotopic ratios. Previous studies have measured variations in presolar grain populations between different matrix regions within the same meteorite thin section. However, most of these studies do not identify if there are any ties between these variations in presolar grain populations and the chemical and mineralogical differences in measured matrix regions. Therefore, the goal of this study is to determine if there is measurable variations in the degree of alteration of different matrix regions within the same thin section, and if mineralogical and chemical changes in matrix regions can be used as indicators for presolar grain preservation. Such a correlation could improve the efficiency of presolar grain identification during searches across large surface areas. To do this, we carried out coordinated scanning electron microscope (SEM) and NanoSIMS analyses, using a new SEM method which measures the ppm concentration of 100 nm to 5 μm sized Mg-, S-, Al-, C- and Ca-rich matrix grains.

presolar grains↗
NASA NTRS1982

Fragmentation of interstellar clouds and star formation

The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

Silk, J.↗
NASA NTRS2012

Carbon Planets

Stellar remnants present unique environments for planet formation, and may host companions with exotic chemistries, like planets made substantially of carbon. I'll provide an overview of carbon planet theory: chemistry, structure and formation scenerios. I'll also describe some recent observations of stellar remnants that have yielded candidate carbon planets.

Kuchner, Marc↗
NASA NTRS1992

Relativistic two-moment neutrino transport

We implement a general relativistic neutrino transport scheme appropriate to problems in stellar collapse and neutron star formation. In this scheme the spectral energy and momentum balance equations are solved as a coupled set. We perform transport calculations on two frozen stellar background models neglecting the feedback of the neutrinos on the matter. We compare with schemes that ignore either relativity or momentum balance or both. The work performed by the neutrino stress on the matter is taken into account and has an important effect. In particular, if there is a hydrodynamical shock in the system, this work contribution boosts the energy deposition behind the shock. This may enhance the chances for a successful neutrino driven supernova explosion.

Cernohorsky, J.↗
NASA NTRS1990

The varieties of symmetric stellar rings and radial caustics in galaxy disks

Numerical, restricted three-body and analytic calculations are used to study the formation and propagation of cylindrically symmetric stellar ring waves in galaxy disks. It is shown that such waves can evolve in a variety of ways, depending on the amplitude of the perturbation and the potential of the target galaxy. Rings can thicken as they propagate outward, remain at a nearly constant width, or be pinched off at large radii. Multiple, closely spaced rings can result from a low-amplitude collision, while an outer ring can appear well-separated from overlapping inner rings or an apparent lens structure in halo-dominated potentials. All the single-encounter rings consist of paired fold caustics. The simple, impulsive, kinematic oscillation equations appear to provide a remarkably accurate model of the numerical simulations. Simple analytic approximations to these equations permit very good estimates of oscillation periods and amplitudes, the evolution of ring widths, and ring birth and propagation characteristics.

Struck-Marcell, Curtis↗
NASA NTRS2004

Selected Papers on Protoplanetary Disks

Three papers present studies of thermal balances, dynamics, and electromagnetic spectra of protoplanetary disks, which comprise gas and dust orbiting young stars. One paper addresses the reprocessing, in a disk, of photons that originate in the disk itself in addition to photons that originate in the stellar object at the center. The shape of the disk is found to strongly affect the redistribution of energy. Another of the three papers reviews an increase in the optical luminosity of the young star FU Orionis. The increase began in the year 1936 and similar increases have since been observed in other stars. The paper summarizes astronomical, meteoric, and theoretical evidence that these increases are caused by increases in mass fluxes through the inner portions of the protoplanetary disks of these stars. The remaining paper presents a mathematical-modeling study of the structures of protostellar accretion disks, with emphasis on limits on disk flaring. Among the conclusions reached in the study are that (1) the radius at which a disk becomes shadowed from its central stellar object depends on radial mass flow and (2) most planet formation has occurred in environments unheated by stellar radiation.

Bell, K. R.↗
NASA NTRS2020

REQUIEM-2D Methodology: Spatially Resolved Stellar Populations of Massive Lensed Quiescent Galaxies from Hubble Space Telescope 2D Grism Spectroscopy

We present a novel Bayesian methodology to jointly model photometry and deep Hubble Space Telescope 2D grism spectroscopy of high-redshift galaxies. Our requiem2d code measures both unresolved and resolved stellar populations, ages, and star formation histories (SFHs) for the ongoing REsolving QUIEscent Magnified (REQUIEM) Galaxies Survey, which targets strong gravitationally lensed quiescent galaxies at z ∼ 2. We test the accuracy of requiem2d using a simulated sample of massive galaxies at z ∼ 2 from the Illustris cosmological simulation and find that we recover the general trends in SFH and median stellar ages. We further present a pilot study for the REQUIEM Galaxies Survey: MRG-S0851, a quintuply imaged, massive (log M ⁎ / M ʘ = 11.02 ± 0.04) red galaxy at z = 1.883 ± 0.001. With an estimated gravitational magnification of µ = 5.7 - 0.2 + 0.4, we sample the stellar populations on 0.6 kpc physical size bins. The global mass-weighted median age is constrained to be 1.8 - 0.2 + 0.3 Gyr, and our spatially resolved analysis reveals that MRG-S0851 has a flat age gradient in the inner 3 kpc core after taking into account the subtle effects of dust and metallicity on age measurements, favoring an early formation scenario. The analysis for the full REQUIEM-2D sample will be presented in a forthcoming paper with a beta release of the requiem2d code.

Strong gravitational lensing↗
NASA NTRS2013

Multiwavelength Observations of Recent Comets

Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth. Comets are comprised of molecular ices, that may be pristine inter-stellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection. We will present a comparison of molecular abundances in these comets to those observed in others, supporting a long-term effort of building a comet taxonomy based on composition.

ground-based observations↗
NASA NTRS2020

Properties and Astrophysical Implications of the 150 M Binary Black Hole Merger GW190521

The gravitational-wave signal GW190521 is consistent with a binary black hole (BBH) merger source at redshift 0.8 with unusually high component masses, 85 (+21,-14) Mꙩ and 66 (+17,-18) Mꙩ, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65–120 Mꙩ. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger (142 (+28,-16) Mꙩ) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular BBH coalescence, we detail the physical properties of GW190521’s source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be 0.13 (+0.30,-0.11)Gp/cu.c yr. We discuss the astrophysical implications of GW190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.

R. Abbott↗
NASA NTRS2013

How Dead are Dead Galaxies? Mid-Infrared Fluxes of Quiescent Galaxies at Redshift 0.3< Z< 2.5: Implications for Star Formation Rates and Dust Heating

We investigate star formation rates of quiescent galaxies at high redshift (0.3 < z < 2.5) using 3D-HST WFC3 grism spectroscopy and Spitzer mid-infrared data. We select quiescent galaxies on the basis of the widely used UVJ color-color criteria. Spectral energy distribution fitting (rest frame optical and near-IR) indicates very low star formation rates for quiescent galaxies (sSFR approx. 10(exp −12)/yr. However, SED fitting can miss star formation if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the mid-infrared. It is therefore fundamental to measure the dust-obscured SFRs with a mid-IR indicator. We stack the MIPS-24 micron images of quiescent objects in five redshift bins centered on z = 0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24 micron detections, we find sSFR approx. 10(exp −11.9) × (1 + z)(sup 4)/yr. These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical star forming galaxies. The true SFRs of quiescent galaxies might be even lower, as we show that the mid-IR fluxes can be due to processes unrelated to ongoing star formation, such as cirrus dust heated by old stellar populations and circumstellar dust. Our measurements show that star formation quenching is very efficient at every redshift. The measured SFR values are at z > 1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels star formation) and well above that at lower redshifts.

Galaxies↗
NASA NTRS2012

The Rise and Fall of Star Formation Histories of Blue Galaxies at Redshifts 0.2 < z < 1.4

Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitor, each with their own unique star formation history (SFH). We use the approach recently developed by Pacifici et al. to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range O.2 < z < 1:4 from the All-Wavelength Extended Groth Strip International Survey (AEGIS). This consists in the Bayesian analysis of the observed galaxy spectral ' energy distributions with a comprehensive library of synthetic spectra assembled using state-of-the-art models of star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We constrain the SFH of each galaxy in our sample by comparing the observed fluxes in the B, R,l and K(sub s) bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFH on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs wIdely used to interpret observed galaxy spectral energy distributions is not appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

Pacifici, Camilla↗
NASA NTRS2020

CO, Water, and Tentative Methanol in η Carinae Approaching Periastron

The complex circumstellar environment around the massive binary and luminous blue variable η Carinae is known to harbor numerous light molecules, emitting most strongly in rotational states with upper level energies to ∼300 K. In circumstellar gas, the complex organic molecule methanol (CH3OH) has been found almost exclusively around young stellar objects, and thus regarded as a signpost of recent star formation. Here we report the first potential detection of methanol around a highly evolved high-mass star, while using the Atacama Large Millimeter Array to investigate molecular cloud conditions traced by CO (2–1) in an orbit phase preceding the 2020 periastron. The methanol emission originates from hot (T(gas) ≃ 700 K) material, ∼2″ (0.02 pc) across, centered on the dust-obscured binary, and is accompanied by prominent absorption of continuum radiation in a cooler (T(gas) ≃ 110 K) layer of gas. We also report a first detection of water in Herschel observations at 557 and 988 GHz. The methanol abundance is several to 50 times higher than observed toward several lower-mass stars, while water abundances are similar to those observed in cool, dense molecular clouds. The very high methanol: water abundance ratio in the core of η Car may suggest methanol formation processes similar to Fischer–Tropschtype catalytic reactions on dust grains. These observations prove that complex molecule formation can occur in a chemically evolved massive stellar environment, given sufficient gas densities and shielding conditions as may occur in material around massive interacting companions and merger remnants.

Patrick W Morris↗
NASA NTRS2014

A Massive Galaxy in Its Core Formation Phase Three Billion Years After the Big Bang

Most massive galaxies are thought to have formed their dense stellar cores at early cosmic epochs. However, cores in their formation phase have not yet been observed. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we present a candidate core in formation 11 billion years ago, at z = 2.3. GOODS-N-774 has a stellar mass of 1.0 × 10 (exp 11) solar mass, a half-light radius of 1.0 kpc, and a star formation rate of 90 (sup +45 / sub −20) solar mass/yr. The star forming gas has a velocity dispersion 317 plus or minus 30 km/s, amongst the highest ever measured. It is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, compact quiescent galaxies at z is approximately equal to 2 (exp 8-11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however, from the star formation rate and size of the galaxy we infer that many star forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

Core↗
NASA NTRS2012

Stellar Populations of Lyman Break Galaxies at z approx. to 1-3 in the HST/WFC3 Early Release Science Observations

We analyze the spectral energy distributions (SEDs) of Lyman break galaxies . (LBGs) at z approx = 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST /WFC3 obse,rvations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z approx = 1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope f3 is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at .z approx = 1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1a uncertainties. This could imply that identical dropout selection technique, at all. redshifts, find physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of approx 0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of approx 0.90. These relations hold true - within luminosities probed in this study - for LBGs from z approx = 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z approx = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z approx = 2 is essential. The future HST UV surveys,. both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

Hathi, N. P.↗