Results for “GRAVITATIONAL INTERACTIONS” — Page 41

NASA NTRS1997

On the Diversity of Planetary Systems

Models of planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. Modern theories of star and planet formation, which are based upon observations of the Solar System and of young stars and their environments, predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed.

Lissauer, Jack J.↗

NASA NTRS1999

Formation and Detection of Planetary Systems

Modern theories of star and planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. The most detailed models of planetary growth are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed, and the methods that are being used and planned for detecting and characterizing extrasolar planets are reviewed.

Lissauer, Jack J.↗

NASA NTRS2002

Planet Formation

Modern theories of star and planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. The most detailed models of planetary growth are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed, and the methods that are being used and planned for detecting and characterizing extrasolar planets are reviewed.

Lissauer, Jack J.↗

NASA NTRS2005

Planet Formation - Overview

Modern theories of star and planet formation are based upon observations of planets and smaller bodies within our own Solar System, exoplanets &round normal stars and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path.

Lissauer, Jack J.↗

NASA NTRS1997

The Birth of Planetary Systems

Models of planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. Modern theories of star and planet formation, which are based upon observations of the Solar System and of young stars and their environments, predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large- enough to gravitationally trap substantial quantities of gas. Another potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed.

Lissauer, Jack J.↗

DOE OSTI2024

Gravitational form factors of charmonia

We investigate the gravitational form factors of charmonium. Our method is based on a Hamiltonian formalism on the light front known as basis light-front quantization. The charmonium mass spectrum and light-front wave functions were obtained from diagonalizing an effective Hamiltonian that incorporates confinement from holographic QCD and one-gluon exchange interaction from light-front QCD. We proposed a quantum many-body approach to construct the hadronic matrix elements of the energy momentum tensor T + + and T + − , which are used to extract the gravitational form factors A ( Q 2 ) and D ( Q 2 ) . The obtained form factors satisfy the known constraints, e.g., the von Laue condition. From these quantities, we also extract the energy, pressure and light-front energy distributions of the system. We find that hadrons are multilayer systems. Published by the American Physical Society 2024

Astronomy & Astrophysics↗

NASA NTRS2010

Mutualism in a Reduced Gravity Environment (MuRGE)

MuRGE (Mutualism in a Reduced Gravity Environment) is a NASA flight-research experiment to investigate the microgravity effects associated with cell-cell communication and beneficial microbe-host interactions using a plant-fungal model system. This investigation will use a clinostat, an instrument that slowly rotates the plants to negate the effects of gravitational pull on plant growth (gravitropism) and development, to simulate microgravity. I will be using the endophytic fungus Piriformospora indica (Pi) and the model plant species Arabidopsis thaliana (At). P. indica has been shown to colonize roots of various plant species, including A. thaliana, and to increase plant growth and resistance to stress. The fungus has the ability to grow from spores or in axenic cultures without the presence of a host. P. indica spores and P. indica extract will be used to inoculate Arabidopsis seeds germinated on a clinostat in order to determine if simulated microgravity affects the interaction between the fungus and its plant host.

Patel, Karishma K.↗

NASA NTRS2010

[Mutualism in a Reduced Gravity Environment (MuRGE)]

MuRGE (Mutualism in a Reduced Gravity Environment) is a NASA flight-research experiment to investigate the microgravity effects associated with cell-cell communication and beneficial microbe-host interactions using a plant-fungal model system. This investigation will use a clinostat, an instrument that slowly rotates the plants to negate the effects of gravitational pull on plant growth (gravitropism) and development, to simulate microgravity. I will be using the endophytic fungus Piriformospora indica (Pi) and the model plant species Arabidopsis thaliana (At). P. indica has been shown to colonize roots of various plant species, including A. thaliana, and to increase plant growth and resistance to stress. The fungus has the ability to grow from spores or in axenic cultures without the presence of a host. P. indica spores and P. indica extract will be used to inoculate Arabidopsis seeds germinated on a clinostat in order to determine if simulated microgravity affects the interaction between the fungus and its plant host.

Patel, Karishma↗

DOE OSTI2015

STAR FORMATION IN TURBULENT MOLECULAR CLOUDS WITH COLLIDING FLOW

Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of –1.35 when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

Neutrino spin oscillations in matter under the influence of gravitational and electromagnetic fields

We derive the new quasi-classical equation for the description of the spin evolution of a neutrino propagating in a curved space-time and interacting with a background matter and an external electromagnetic field. This equation is used to analyze neutrino spin oscillations in these external backgrounds. We obtain the effective Hamiltonian and the transition probability for oscillations of neutrinos when they move in the vicinity of a rotating black hole, surrounded by an accretion disk, and interact with an external magnetic field. The appearance of new resonances in neutrino spin oscillations in this system is considered. The approximate treatment of spin oscillations of radially propagating ultra high energy neutrinos is developed. We also discuss the applications of our results to the description of neutrino spin oscillations in realistic astrophysical media.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Classical gluon and graviton radiation from the bi-adjoint scalar double copy

We find double-copy relations between classical radiating solutions in Yang-Mills theory coupled to dynamical color charges and their counterparts in a cubic bi-adjoint scalar field theory which interacts linearly with particles carrying bi-adjoint charge. The particular color-to-kinematics replacements we employ are motivated by the Bern-Carrasco-Johansson double-copy correspondence for on-shell amplitudes in gauge and gravity theories. They are identical to those recently used to establish relations between classical radiating solutions in gauge theory and in dilaton gravity. Our explicit bi-adjoint solutions are constructed to second order in a perturbative expansion, and map under the double copy onto gauge theory solutions which involve at most cubic gluon self-interactions. If the correspondence is found to persist to higher orders in perturbation theory, our results suggest the possibility of calculating gravitational radiation from colliding compact objects, directly from a scalar field with vastly simpler (purely cubic) Feynman vertices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Cosmography of Generalized Ghost Dark Energy Model in f(G) Gravity

This paper is devoted to construction of generalized ghost dark energy f(G) model by using correspondence scheme for both interacting and noninteracting scenarios with pressureless matter and power-law scale factor. We study the cosmological implications of the resulting model through equation of state parameter and ω{sub DE} – ω{sub DE}{sup ′} as well as r – s plane. We also discuss stability of the resulting model through squared speed of sound parameter. The equation of state parameter represents phantom phase of the Universe for both cases while the squared speed of sound indicates stability of this model. The ω{sub DE} – ω{sub DE}{sup ′} plane represents thawing region whereas r – s plane corresponds to phantom and quintessence DE regimes for both interacting and noninteracting cases.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Quantum Monte Carlo Methods for Astrophysical Applications

In recent years, new astrophysical observations have provided a wealth of exciting input for nuclear physics. For example, the observations of two-solar-mass neutron stars put strong constraints on possible phase transitions to exotic phases in strongly interacting matter at high densities. Furthermore, the recent observation of a neutron-star merger in both the electromagnetic spectrum and gravitational waves has provided compelling evidence that neutron-star mergers are an important site for the production of extremely neutron-rich nuclei within the r-process. In the coming years, an abundance of new observations is expected, which will continue to provide crucial constraints on the nuclear physics of these events. To reliably analyze such astrophysical observations and extract information on nuclear physics, it is very important that a consistent approach to nuclear systems is used. Such an approach consists of a precise and accurate method to solve the nuclear many-body problem in nuclei and nuclear matter, combined with modern nuclear Hamiltonians that allow to estimate the theoretical uncertainties. Quantum Monte Carlo methods are ideally suited for such an approach and have been successfully used to describe atomic nuclei and nuclear matter. In this contribution, I will present a detailed description of Quantum Monte Carlo methods focusing on the application of these methods to astrophysical problems. In particular, I will discuss how to use Quantum Monte Carlo methods to describe nuclear matter of relevance to the physics of neutron stars.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1986

Have burnt-out galaxies and galaxy clusters been detected?

It is shown here that an elevated rate of star formation may be responsible for burning out protogalaxies in the densest galaxy clusters, leading to the formation of candidate gravitational lenses and to an enhanced probability of close association of quasars in regions of apparently low galaxy density. Extreme tidal interactions occurring during the initial collapse of such clusters would stimulate the star formation and also could drive molecular clouds and stars onto radial orbits, fuelling massive black holes and leading to an enhanced frequency of occurrence of quasar pairs. It is argued that a fundamental bias exists against detecting luminous matter in the great galactic clusters.

Silk, Joseph↗

NASA NTRS1993

Evolution of planetesimals. I - Dynamics: Relaxation in a thin disk. II - Numerical simulations

The study examines the effects of density inhomogeneity and differential rotation as well as inelastic collisions on the dynamical evolution of planetesimals. Consideration is given to a three-step analysis: the dynamical evolution of the planetesimals, collisions and mass accumulation, and interaction with gas. It is shown that the velocity dispersion of a cold system of planetesimals increases rapidly due to elastic gravitational scattering. When the dispersion in the epicycle amplitude becomes comparable to the planetesimals' Roche radius, energy is transferred from the systematic Keplerian shear to the dispersive motion. With a numerical N-body scheme, gravitational scattering and physical collisions among a system of planetesimals is simulated. It is shown that dynamical equilibrium is attained with a velocity dispersion comparable to the surface escape velocity of those planetesimals which contribute most of the system mass.

Palmer, P. L.↗

NASA NTRS1994

Investigation relative to the Roentgen Satellite (ROSAT)

Reports include: High Resolution Observations of the Central Region of M31; The X-ray Emission of Low-X-ray-Luminosity Early-Type Galaxies: Gas Versus Compact Sources; Interaction Between Cluster Gas and Radio Features of Cygnus A; Hot Gas and Dark Halos in Early-Type Galaxies; A Gravitational Lens in X-rays - 0957+461; How Massive are Early-Type Galaxies?; Three Crab-Like SNR in the Large Magellanic Cloud; and Soft X-ray Emission from Boundary Layers in Cataclysmic Variables. Papers submitted to the Astrophysical Journal are attached.

Elvis, Martin S.↗

NASA NTRS2003

Optical measurements of gravity fields

Optical measurements of a gravitational field with sensitivity close to the sensitivity of atomic devices are possible if one detects properties of light after its interaction with optically thick atomic cloud moving freely in the gravity field. A nondestructive detection of a number of ultracold atoms in a cloud as well as tracking of the ground state population distribution of the atoms is possible by optical means.

whispering gallery modes microwave detection modul↗

NASA NTRS2011

Method and Apparatus for the Quantification of Particulate Adhesion Forces on Various Substrates

Mitigation strategies for lunar dust adhesion have typically been limited to qualitative analysis. This technical memorandum describes the generation and operation of an adhesion testing device capable of quantitative assessment of adhesion forces between particulates and substrates. An aerosolization technique is described to coat a surface with a monolayer of particulates. Agitation of this surface, via sonication, causes particles to dislodge and be gravitationally fed into an optical particle counter. Experimentally determined adhesion force values are compared to forces calculated from van der Waals interactions and are used to calculate the work of adhesion using Johnson-Kendall-Roberts (JKR) theory. Preliminary results indicate that a reduction in surface energy and available surface area, through topographical modification, improve mitigation of particulate adhesion.

Wohl, Christopher J.↗