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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 NTRS1971

An Eotvos experiment in earth orbit

The gravitational interactions of mass energy stored in the weak interaction are being investigated. The magnitude of possible Eotvos anomalies, such as weak interaction, gravitational self-energy, spin-orbit interactions, and electromagnetic radiation reaction, are considered. A sensitive experiment was designed to determine whether weak interaction energy violates the equivalence principle. Factors to be considered in spacecraft design for the experiment are presented.

Chapman, P. K.↗
NASA NTRS2003

Density Anomalies in the Mantle and the Gravitational Core-Mantle Interaction

Seismic studies suggest that the bulk of the mantle is heterogeneous, with density variations in depth as well as in horizontal directions (latitude and longitude). This density variation produces a three- dimensional gravity field throughout the Earth. On the other hand, the core density also varies in both time and space, due to convective core flow. Consequently, the fluid outer core and the solid mantle interact gravitationally due to the mass anomalies in both regions. This gravitational core-mantle interaction could play a significant role in exchange of angular momentum between the core and the mantle, and thus the change in Earth's rotation on time scales of decades and longer. Aiming at estimating the significance of the gravitational core-mantle interaction on Earth's rotation variation, we introduce in our MoSST core dynamics model a heterogeneous mantle, with a density distribution derived from seismic results. In this model, the core convection is driven by the buoyancy forces. And the density variation is determined dynamically with the convection. Numerical simulation is carried out with different parameter values, intending to extrapolate numerical results for geophysical implications.

Kuang, Weijia↗
NASA NTRS1993

Deep H alpha images of interacting galaxies

Gravitational interactions between galaxies are believed to increase star formation activity dramatically, and most of the brightest starburst galaxies show clear signs of recent interactions. However, it is still not known how interaction triggers star formation, nor are there models to relate the type or strength of interaction to the location or amount of star formation. We report on a series of deep H alpha images of interacting and post-interaction galaxies which we took with the purpose of finding the young stars and ionized gas in these objects. We were motivated in part by the hope that by studying the very recently formed stars we could see how the interaction process had affected the star formation. We observed the galaxies through 50 A-wide filters, one on the redshifted H alpha line and one off, and a standard R filter. Depending on the galaxy and conditions, images in the B, V, and I filters were also obtained. The images were recorded with a 4x7 ft. or 17 ft. diameter CCD at the 1-meter telescope of the Wise Observatory in Mitzpe Ramon. The H alpha and continuum images are used, together with observations at other wavelengths, to put together as complete a picture as possible of star formation and interactions in each galaxy. The complete observation set is not yet available for all the galaxies but certain results are already clear. There do not seem to be any correlations between H 1 and H alpha structures. In some H 1 plume galaxies H alpha extensions were seen on the other side of the galaxy from the H 1; in others extensive H alpha filaments have been found but not H 1. The preliminary results agree with the simplest model that interaction-induced star formation will be concentrated in the system center, since that is where the mass ends up.

Beck, S. C.↗
DOE OSTI2017

A Librational Model for the Propeller Blériot in the Saturnian Ring System

The reconstruction of the orbital evolution of the propeller structure Blériot orbiting in Saturn’s A ring from recurrent observations in Cassini ISS images yielded a considerable offset motion from the expected Keplerian orbit. This offset motion can be composed by three sinusoidal harmonics with amplitudes and periods of 1845, 152, 58 km and 11.1, 3.7, and 2.2 years, respectively. In this paper we present results from N -body simulations, where we integrated the orbital evolution of a moonlet, which is placed at the radial position of Blériot under the gravitational action of the Saturnian satellites. Our simulations yield that, especially the gravitational interactions with Prometheus, Pandora, and Mimas are forcing the moonlet to librate with the right frequencies, but the libration amplitudes are too small to explain the observations. Thus, further mechanisms are needed to explain the amplitudes of the forced librations—e.g., moonlet–ring interactions. Here, we develop a model, where the moonlet is allowed to be slightly displaced with respect to its created gaps breaking the point symmetry and causing a repulsive force in this way. As a result, the evolution of the moonlet’s longitude can be described by a harmonic oscillator. In the presence of external forcing by the outer moons, the libration amplitudes get the more amplified the closer the forcing frequency is to the eigenfrequency of the disturbed propeller oscillator. Applying our model to Blériot, it is possible to reproduce a libration period of 13 years with an amplitude of about 2000 km.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Probing gravitational dark matter

So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χ{sub s}. It is a ℤ{sub 2} odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξ{sub s}χ{sub s}{sup 2}R, where ξ{sub s} is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξ{sub s}χ{sub s}{sup 2}R, together with Higgs-curvature nonminimal coupling term ξ{sub h}H{sup †}HR, induces effective couplings between χ{sub s}{sup 2} and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between the optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

The gravitomagnetic interaction and its relationship to other relativistic gravitational effects

To better understand the relationship between the expected precession rates of an orbiting gyroscope (GP-B) and other observable consequences in the solar system of relativistic, post-Newtonian gravity, a phenomenological model was developed of post-Newtonian gravity which presupposes the very minimum possible concerning the nature and foundations of the gravitational interaction. Solar system observations, chiefly interplanetary ranging, fix all the parameters in the phenomenological model to various levels of precision. This permits prediction of gyroscope precession rates to better than 10 pct. accuracy. A number of new precession terms are calculated which would exist if gravity were not a metric field phenomenon, but this would clash with other empirical observations of post-Newtonian effects in gravity. It is shown that gravitomagnetism, the post-Newtonian gravitational corrections to the interactions between moving matter, plays a ubiquitous role in determining a wide variety of gravitational effects, including the precession of orbiting gyroscopes.

Nordtvedt, Kenneth↗
DOE OSTI2015

FORMATION OF MULTIPLE-SATELLITE SYSTEMS FROM LOW-MASS CIRCUMPLANETARY PARTICLE DISKS

Circumplanetary particle disks would be created in the late stage of planetary formation either by impacts of planetary bodies or disruption of satellites or passing bodies, and satellites can be formed by accretion of disk particles spreading across the Roche limit. Previous N-body simulation of lunar accretion focused on the formation of single-satellite systems from disks with large disk-to-planet mass ratios, while recent models of the formation of multiple-satellite systems from disks with smaller mass ratios do not take account of gravitational interaction between formed satellites. In the present work, we investigate satellite accretion from particle disks with various masses, using N-body simulation. In the case of accretion from somewhat less massive disks than the case of lunar accretion, formed satellites are not massive enough to clear out the disk, but can become massive enough to gravitationally shepherd the disk outer edge and start outward migration due to gravitational interaction with the disk. When the radial location of the 2:1 mean motion resonance of the satellite reaches outside the Roche limit, the second satellite can be formed near the disk outer edge, and then the two satellites continue outward migration while being locked in the resonance. Co-orbital satellites are found to be occasionally formed on the orbit of the first satellite. Our simulations also show that stochastic nature involved in gravitational interaction and collision between aggregates in the tidal environment can lead to diversity in the final mass and orbital architecture, which would be expected in satellite systems of exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Gravitational Contact Interactions and the Physical Equivalence of Weyl Transformations in Effective Field Theory

Theories of scalars and gravity, with non-minimal interactions, $\sim (M_P^2 +F(\phi) )R +L(\phi)$, have graviton exchange induced contact terms. These terms arise in single particle reducible diagrams with vertices $\propto q^2$ that cancel the Feynman propagator denominator $1/q^2$ and are familiar in various other physical contexts. In gravity these lead to additional terms in the action such as $\sim F(\phi) T_\mu^\mu(\phi)/M_P^2$ and $F(\phi)\partial^2 F(\phi)/M_P^2$. The contact terms are equivalent to induced operators obtained by a Weyl transformation that removes the non-minimal interactions, leaving a minimal Einstein-Hilbert gravitational action. This demonstrates explicitly the equivalence of different representations of the action under Weyl transformations, both classically and quantum mechanically. To avoid such "hidden contact terms" one is compelled to go to the minimal Einstein-Hilbert representation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Gravity as a portal to reheating, leptogenesis and dark matter

We show that a minimal scenario, utilizing only the graviton as an intermediate messenger between the inflaton, the dark sector and the Standard Model (SM), is able to generate simultaneously the observed relic density of dark matter (DM), the baryon asymmetry through leptogenesis, as well as a sufficiently hot thermal bath after inflation. We assume an inflaton potential of the form V(Φ) ∝ Φ k about the minimum at the end of inflation. The possibility of reheating via minimal gravitational interactions has been excluded by constraints on dark radiation for excessive gravitational waves produced from inflation. We thus extend the minimal model in several ways: i) we consider non-minimal gravitational couplings — this points to the parameter range of DM masses M N 1 ≃ 2–10 PeV, and right-handed neutrino masses M N 2 ≃ (5–20) × 10 11 GeV, and T RH ≲ 3 × 10 5 GeV (for k ≤ 20); ii) we propose an explanation for the PeV excess observed by IceCube when the DM has a direct but small Yukawa coupling to the SM; and iii) we also propose a novel scenario, where the gravitational production of DM is a two-step process, first through the production of two scalars, which then decay to fermionic DM final states. In this case, the absence of a helicity suppression enhances the production of DM and baryon asymmetry, and allows a great range for the parameters including a dark matter mass below an MeV where dark matter warmness can be observable by cosmic 21-cm lines, even when gravitational interactions are responsible for reheating. We also show that detectable primordial gravitational wave signals provide the opportunity to probe this scenario for T RH ≲ 5 × 10 6 GeV in future experiments, such as BBO, DECIGO, CE and ET.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1982

Interaction of gravitic and mechanical stimuli in tropic and nastic responses in beans

Experiments designed to explore the interaction of gravity and mechanical stimuli in the tropic and nastic movements of Cherokee Bush bean plants were summarized. When 10-day-old plants were rubbed just prior to presentation of the gravitic stimulus (by placing them on their sides), they displayed much less geotropic curvature than did nonrubbed controls. Geotropism could also be inhibited by rubbing even after it had been progressing for two hours. Wind from a fan could also inhibit geotropism, suggesting that this phenomenon also occurs in nature.

Jaffe, M. J.↗
DOE OSTI2017

Gravity-mediated dark matter annihilation in the Randall-Sundrum model

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examine constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

STABILITY OF THE OUTER PLANETS IN MULTIRESONANT CONFIGURATIONS WITH A SELF-GRAVITATING PLANETESIMAL DISK

We study the effect of a massive planetesimal disk on the dynamical stability of the outer planets in a system representing the early solar system assuming, as has been suggested recently, that these planets were initially locked in a compact and multiresonant configuration as a result of gas-driven migration in a protoplanetary disk. The planetesimal disk is represented by an ensemble of 2000 lunar mass bodies for which the gravitational interaction is calculated self-consistently using the Mercury6.5 code. Several initial multiresonant configurations and planetesimal disk models are considered. Under such conditions a strong dynamical instability, manifested as a rapid giant planet migration and planetesimal disk dispersal, develops on a timescale of less than 40 Myr in most cases. Dynamical disk heating due to the gravitational interactions among planetesimals leads to more frequent interactions between the planetesimals and the ice giants, in comparison to models in which planetesimal–planetesimal interactions are neglected. The number of particles used to represent the planetesimal disk has implications for our results, and although our studies represent the first self-consistent calculations of unstable planetesimal-driven migration, our results point toward the need for using more realistic treatments of the planetesimal disk. Finally, in the framework of our model, we discuss the possible implications of our results on the early evolution of the solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Detection and Characterization of Extrasolar Planets through Mean-motion Resonances. II. The Effect of the Planet’s Orbital Eccentricity on Debris Disk Structures

Structures observed in debris disks may be caused by gravitational interaction with planetary or stellar companions. These perturbed disks are often thought to indicate the presence of planets and offer insights into the properties of both the disk and the perturbing planets. Gaps in debris disks may indicate a planet physically present within the gap, but such gaps can also occur away from the planet’s orbit at mean-motion resonances (MMRs), and this is the focus of our interest here. We extend our study of planet–disk interaction through MMRs, presented in an earlier paper, to systems in which the perturbing planet has moderate orbital eccentricity, a common occurrence in exoplanetary systems. In particular, a new result is that the 3:1 MMR becomes distinct at higher eccentricity, while its effects are absent for circular planetary orbits. We also only consider gravitational interaction with a planetary body of at least 1 M {sub J}. Our earlier work shows that even a 1 Earth mass planet can theoretically open an MMR gap; however, given the narrow gap that can be opened by a low-mass planet, its observability would be questionable. We find that the widths, locations, and shapes of two prominent structures, the 2:1 and 3:1 MMRs, could be used to determine the mass, semimajor axis, and eccentricity of the planetary perturber and present an algorithm for doing so. These MMR structures can be used to narrow the position and even determine the planetary properties (such as mass) of any inferred but as-yet-unseen planets within a debris disk. We also briefly discuss the implications of eccentric disks on brightness asymmetries and their dependence on the wavelengths with which these disks are observed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Heavy spin-2 Dark Matter

We provide further details on a recent proposal addressing the nature of the dark sectors in cosmology and demonstrate that all current observations related to Dark Matter can be explained by the presence of a heavy spin-2 particle. Massive spin-2 fields and their gravitational interactions are uniquely described by ghost-free bimetric theory, which is a minimal and natural extension of General Relativity. In this setup, the largeness of the physical Planck mass is naturally related to extremely weak couplings of the heavy spin-2 field to baryonic matter and therefore explains the absence of signals in experiments dedicated to Dark Matter searches. It also ensures the phenomenological viability of our model as we confirm by comparing it with cosmological and local tests of gravity. At the same time, the spin-2 field possesses standard gravitational interactions and it decays universally into all Standard Model fields but not into massless gravitons. Matching the measured DM abundance together with the requirement of stability constrains the spin-2 mass to be in the 1 to 100 TeV range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

DISCOVERY OF A GAS-RICH COMPANION TO THE EXTREMELY METAL-POOR GALAXY DDO 68

We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z {sub ☉}, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M{sub H} {sub I} = 2.8 × 10{sup 7} M {sub ☉}), recently star-forming (SFR{sub FUV} = 1.4 × 10{sup –3} M {sub ☉} yr{sup –1}, SFR{sub Hα} < 7 × 10{sup –5} M {sub ☉} yr{sup –1}) companion has the same systemic velocity as DDO 68 (V {sub sys} = 506 km s{sup –1}; D = 12.74 ± 0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2001

Formation of Planetary Systems

Stars are observed to be forming within cold regions of the galaxy called molecular clouds. A clump of gas and dust within a molecular cloud can collapse into a rotationally- supported disk orbiting the pre s sure -supported star. Such a disk has the same initial elemental composition as the growing star. At sufficient distances from the central star, it is cool enough for approx. 1 - 2% of this material to be in solid form, either remnant interstellar grains or condensates formed within the disk. During the infall stage, the disk is very active and probably highly turbulent. When the infall slows substantially or stops, the disk becomes more quiescent. The dust grows from micron-sized dust to kilometer-sized planetesimals by physical collisions, possibly aided by collective gravity. The dynamics of larger solid bodies within protoplanetary disks are better characterized. The primary perturbations on the orbits of kilometer-sized and larger planetesimals in protoplanetary disks are mutual gravitational interactions and physical collisions. These interactions lead to accretion (and in some cases erosion and fragmentation) of planetesimals. The most massive planets have the largest gravitationally-enhanced collision cross-sections, and accrete almost everything with which they collide. The size distribution of solid bodies becomes quite skewed, with a few large bodies growing much faster than the rest of the swarm, until they have accumulated most of the small bodies within their gravitational reach. Slower growth continues (at least for solid, earth-like planets) as the eccentricities of planetary embryos are pumped up by long-range mutual gravitational perturbations. As planetary masses increase, they become more efficient at stirring random velocities of neighboring bodies. If sufficiently massive and dense planets exist far enough from the star, they can eject material into interstellar space. In most models, giant planets begin their growth like terrestrial planets, but if they become massive enough before the protoplanetary disk dissipates, then they are able to accumulate substantial amounts of gas. Giant planet growth times predicted by current models are similar to estimates of the lifetime of the gaseous protoplanetary disk, so we don't know whether or not giant planets form in most protoplanetary disks. However, planets that become massive while a substantial amount of gas remains in the disk may migrate into the star as a consequence of their gravitational interactions with the disk.

Lissauer, Jack J.↗