The formation and evolution of an accretion disk formed during the collapse of a rotating cloud core
NASA Technical Reports Server (NTRS)
Material falling (accreting) onto a black hole in a binary system, or at the center of a galaxy, forms an accretion disk about the event horizon, with the inner ...
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Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is
planet :: smoking gun : caught in the actsmoking gun : caught in the act Most simulations of disk-planetDisk Instability vsvs. Core Accretion. Core Accretion Formed planet : forming planet ::Formed planet : formingMost simulations of ...
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A new branch of equilibrium solutions for stationary accretion disks around black holes is found. These solutions correspond to moderately super-Eddington accretion rates. The existence of the new branch is a consequence of an additional cooling due to general relativistic Roche lobe overflow and horizontal advection of heat. On an ...
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Formation and Evolution of Planetary Systems Beichman et al. 3. A. How do Planets Form: Core accretion vs. Disk Fragmentation? The core accretion model of ...
Dec 6, 2007 ... "Our computer simulations show that the ridges must have accreted rapidly when Saturn's rings were thin, forming small accretion disks ...
Recently, Ida et al. made an N-body simulation of lunar accretion from a protolunar disk formed by a
In this paper, we study the physical properties and characteristics of matter forming thin accretion disks in static and spherically symmetric wormhole spacetimes. In particular, the time averaged energy flux, the disk temperature, and the emission spectra of the accretion ...
The nature of linear perturbations to a thin, shearing accretion disk composed of compressible material is reexamined. Modes that can carry angular momentum throughout the disk are identified, and it is shown how the subsequent dissipation of these waves through nonlinear processes can form the basis of a viscosity ...
Apr 12, 2011 ... The characteristics of a particular planetary system depend upon the ... planets are formed from dynamic instabilities in accretion disks. ...
Neutron Stars, Pulsars, Millisecond Pulsars, and Gravitational Radiation: GLOSSARY. Accretion disk: The flattened, pancake-like structure formed by matter ...
We aim to monitor T Tauri star disk emission features and jet outflow morphologies to determine how these features vary with disk accretion rate, and how and when the outflow responds to major accretion events. Young stars are surrounded by circumstellar disks through which they ...
NASA Astrophysics Data System (ADS)
(� \\Gamma5 km s \\Gamma1 ), possibly associated with a disk wind or magnetic accretion columns. The velocity (Beckwith and Sargent, 1993; Strom et al. 1993). Evidence that these disks accrete onto the stellar surface protostellar disks form and evolve (Strom, Edwards and ...
An effort is made to observationally constrain accretion disks on the basis of light curves from the eclipsing cataclysmic variable UX Ursae Majoris, reconstructing the spectral energy distribution across the face of an accretion disk. The spectral resolution obtained suffices to reveal not only the radial ...
accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...
Oct 29, 2010 ... Stars formed, planetary systems around stars formed from within these ... Kepler is observing accretion disks with a combined photometric ...
Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks
We calculate the structure of an effectively optically thin and geometrically thin accretion disk in
A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed
The notion that planetary systems are formed within dusty disks is certainly not a new one; the modern planet formation paradigm is based on suggestions made by Laplace more than 200 years ago. More recently, the foundations of accretion disk theory where...
National Technical Information Service (NTIS)
accretion? " What is the structure of the inner disk? " How do accretion disks drive jets? ... IXO will reveal the physics of disk accretion, and low L_X ...
The most massive stars can form via standard disk accretion�despite the radiation pressure generated�due to the fact that the massive accretion disk yields a strong anisotropy in the radiation field, releasing most of the radiation pressure perpendicular to the disk ...
Results of two-dimensional gas dynamic computations of gas flow in symbiotic stars are presented, with radiation cooling of gas in the forming accretion disk taken into consideration. As computations show, radiation cooling does not change qualitatively the picture of the flow in the vicinity of the accreting star. ...
Accretion Disks around Stars and the Process of Planet Formation National Radio Astronomy. This process is regulated by ejecting gas in "jet-like" outflows. II. Planets form later from the remnants of the disk. Planets may only form when conditions around the star are "just right." III. Planets ...
Most Galaxy-sized systems (M host sime 1012 M sun) in the ?CDM cosmology are expected to have interacted with at least one satellite with a total mass M sat sime 1011 M sun sime 3M disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of accretion for the survival of thin galactic ...
We construct a model of a geometrically thick accretion disk orbiting a 10 M/sub sun/ black hole in which most of the interior is in convective equilibrium, and in which the accretion flow and heat generation are confined mostly to the layers due to the equatorial plane. Surfaces of constant angular momentum and surfaces of constant ...
Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a ...
PubMed
... from a bipolar jet that has formed near the point where material streaming from star 2 interacts with the accretion disk around star 1 (Harmanec et al. ...
DTIC Science & Technology
Feb 23, 2004 ... The gas spirals toward the neutron star like water going down a drain, forming what scientists call an accretion disk. ...
Matter spirals toward the neutron star in the form of an accretion disk, a journey visible in X-ray radiation. In doing so, it transfers its orbital energy to the neutron ...
Material in the core of the disk starts forming a new star. ... These planetesimals in turn collide and accrete new material, eventually building up into ...
... Hamilton 2001; Hansen 2002), but all generally rely on an accretion disk around the pulsar within which the planets form. Millisecond pulsars are a ...
High Energy Astrophysics: Accretion Disks II 1/59 Accretion Disks II 1 The dynamical equations Astrophysics: Accretion Disks II 2/59 The simplest accretion disc model to construct is that of the thin disc on the azimuthal angle z #12;High Energy ...
The dynamics and structure of accretion disks, which accumulate a vertical magnetic field in their centers, are investigated using two- and three-dimensional MHD simulations. The central field can be built up to the equipartition level, where it disrupts a nearly axisymmetric outer accretion disk inside a ...
We have studied the dependence of the profiles of molecular abundances and line emission on the accretion flow in the hot ($\\ga 100$K) inner region of protoplanetary disks. The gas-phase reactions initiated by evaporation of the ice mantle on dust grains are calculated along the accretion flow. We focus on methanol, a molecule that is ...
Disk accretion onto a magnetized spinning neutron star or a white dwarf will not be possible if the radius of the magnetosphere exceeds the corotation radius. A dead disk serving as a reservoir of material will then form around the star. Such a disk could retard the spin of the star; it might ...
data yield the accretion disk thickness, diameter, electron density, and magnetic field. Introduction. The structure of AGN accretion disks on sub-parsec ...
The structure of AGN accretion disks on sub-parsec scales can be probed t,hrough ... GHz to map absorption caused by an inner accretion disk. ...
Nov 19, 2004 ... In an accretion disk, material near the outside moves slower than ... Depending on the angle at which we observe the accretion disk, ...
Jan 29, 2010 ... KY Relativistic Accretion Disk models. A set of models from Dovciak et al. (2004 ) for accretion disk spectra in the strong gravity regime. ...
do not have accretion disks. Optical spectra are the only way that we can .... inner accretion disks) confirms the asymmetrical distribution of such stars ...
Sep 27, 2002 ... Accretion Disk Simulation ... Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material ...
Slim-disk models describe advective accretion flows at high luminosities, while reducing to the standard thin disk form in the low luminosity limit. We have developed a new spectral model, slimbb, within the framework of XSPEC, which describes fully relativistic slim-disk ...
Context. Models of the formation, evolution and photoevaporation of circumstellar disks are an essential ingredient in many theories of the formation of planetary systems. The ratio of disk mass over stellar mass in the circumstellar phase of a disk is for a large part determined by the angular momentum of the original cloud core from ...
Current models of planet and satellite formation aremarred by our lack of understanding regarding the turbulent state of accretion disks. According to the Rayleigh criterion, Keplerian disks are hydrodynamically stable. Indeed, it has been argued that a c...
High Energy Astrophysics: Accretion Disks I 1/60 Accretion Disks I References: Accretion Power in Astrophysics, J. Frank, A. King and D. Raine. High Energy Astrophysics, Vol. 2, M.S. Longair, Cambridge Astrophysics: Accretion Disks I 2/60 1 Overview ...
One possible mechanism for giant planet formation is disk instability in which the planet is formed as a result of gravitational instability in the protoplanetary disk surrounding the young star. The final composition and core mass of the planet will depend on the planet's mass, environment, and the planetesimal ...
If an isolated black hole is massive enough and if it accretes matter at a fast enough rate, the outer parts of the accretion disk will become self-gravitating and may become unstable, disintegrating into fragments which could form separate stars. The fragmentation would produce around the black hole a ring of gas ...
This is the first of two papers that investigate models of radiation-driven winds from super-critical accretion disks. The main assumptions in the models are that the mass and luminosity in the wind emanate from the radius in the disk where accretion becomes supercritical (the critical radius) and that the wind is ...
Disks, Accretion. USE. ACCRETION DISKS. Disks, Optical. USE. VIDEO DISKS. Disposal (In Space), Hazardous Material. USE. HAZARDOUS MATERIAL DISPOSAL (IN ...
A disk model with gas pressure viscosity. The spectrum from an accretion disk ... viscosity scales as the gas pressure. From Stella and Rosner 1984, ApJ, ...
Fully self consistent calculations of the spectra emitted by active galactic nuclei accretion disks are presented. The inner, radiation dominated regions of standard, alpha disks are treated. Incoherent Compton scattering and emission/absorption of radiation by hydrogen and helium are included in computing the vertical temperature ...
Emission-line profiles of several cataclysmic variables have been observed through eclipse, and they do not show strong evidence for the rotational signature that is characteristic of an accretion disk. The lines appear to be formed in material that has some rotation with respect to the white dwarf, but that also has a substantial ...
It is fairly common consensus that circumstellar disks are near-ubiquitously present around stars at birth. These disks are the sites of planetary formation, and with detection of exo-solar planets now occurring routinely, understanding of the evolutionary link between young circumstellar disks and planets is more critical than ever. ...
The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this ...
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was
Equations for the structure and appearance of supercritical accretion disks and the radiation-driven
An effort is made to observationally constrain accretion disks on the basis of light curves from the
A possible accretion model associated with the ionization instability of quasar disks is proposed to
Active galactic nuclei are believed to be powered by accretion through a disk onto a super-massive black hole at the center of the host galaxy. Luminous quasars then require accretion rates of one to ten solar masses per year. I will show that this requires disk surface densities of order 400 grams per square ...
Accretion disks are among the most luminous and ubiquitous sources in astrophysics and they have drawn a good deal of attention from the observational and theoretical communities. In this paper, we study the process of matter forming thin accretion disks around black hole solutions in the ...
We consider the effects of ``photon bubble'' shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of ...
Context. Even though turbulent motions are found everywhere in astrophysical systems, the origin of this turbulence is poorly understood. When cosmic structures form, they grow in mass via accretion from their surrounding environment. Aims: We propose that accretion is able to drive internal turbulent motions in a wide range of ...
``Corrugated'' plasma disks can form in the dominant gravity of a central object when the peak plasma pressure in the disk is of the same order as that of the pressure of the ``external'' magnetic field, while the magnetic field resulting from internal plasma currents is of the same order as the external field. The corrugation refers ...
We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal component of the magnetic ...
Three-dimensional numerical simulations of gas dynamics are used to study the flow pattern in a close binary system after it has reached the steady-state accretion regime. The special attention is paid to physics of accretion disks in binary systems and, particularly, the waves in disks. It is shown that in systems ...
Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...
Sep 4, 1998 ... 3. Formation of an Accretion Disk. Bonnet-Bidaud and van der Klis (1979) showed that even if the accretion is from the stellar wind, ...
A scenario for the central engine of AGN has been developed consisting of a massive black hole (MBH) onto which gas accretes through an accretion disk. The accretion disk radiates the observed optical and ultraviolet continua. Surrounding the MBH is a nonthermal source which produces the ...
We propose a new evolutionary model of a supermassive black hole (SMBH) and a circumnuclear disk (CND), taking into account the mass-supply from a host galaxy and the physical states of CND. In the model, two distinct accretion modes depending on gravitational stability of the CND play a key role on accreting gas to a SMBH. (i) If the ...
The UBVR light curves of the massive eclipsing binary RY Sct, obtained at the Maidanak Observatory from 1979 to 1992, have been re-analyzed in order to prove the hypothesis of the presence of an accretion disk in the system. This hypothesis is supported by a new spectroscopic study of Grundstrom et al., and by a specific light-curve shape exhibiting a ...
A scenario for the central engine of AGN has been developed, consisting of a massive black hole (MBH) onto which gas accretes through an accretion disk. The accretion disk radiates the observed optical and ultraviolet continua. Surrounding the MBH is a no...
(Abridged) We perform dissipationless N-body simulations to elucidate the dynamical response of thin disks to bombardment by cold dark matter (CDM) substructure. Our method combines (1) cosmological simulations of the formation of Milky Way (MW)-sized CDM halos to derive the properties of substructure and (2) controlled numerical experiments of consecutive subhalo impacts onto ...
290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...
They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...
accretion disk where the viscosity is dominated by radiation pressure. ... viscosity norm. 2. 2cos /i d where i is the inclination of the disk and d is the ...
Using resistive magnetohydrodynamics simulation, we consider circumstellar disk formation in a strongly magnetized cloud. As the initial state, an isolated cloud core embedded in a low-density interstellar medium with a uniform magnetic field was adopted. The cloud evolution was calculated until almost all gas inside the initial cloud fell onto either the circumstellar ...
We study the accretion from a primordial gaseous disk onto an embedded planet. Our code solves the local Hill equations in Cartesian and polar coordinates centered on the planet using an adaptive grid with additional levels of refinement inside the Hill sphere. A circumplanetary disk forms inside the Hill ...
Observations of X-ray binaries indicate substantial half-thicknesses for the accretion disks in these systems (up to h/R ? 0.25, where h is the disk half-thickness and R its radius), while standard ? accretion disks predict appreciably smaller half-thicknesses. We study the theoretical vertical ...
Recent theoretical advances in our understanding of the dynamics of circumstellar accretion disks are reviewed. Of particular importance are developments regarding angular momentum transport processes in disks. It has recently been shown through direct numerical simulation that vertical convection results in inward transport, and thus ...
The observed contraction of the accretion disks in the dwarf novae U Gem and Z Cha during quiescence is interpreted with simple dynamical models. The standard {alpha}-parameter viscosity prescription is replaced by macroscopic constraints that are both computationally convenient and appropriate for the study of an extensive characteristic such as the ...
Accretion disks are associated with such diverse objects as planetary systems, Be stars, and spiral galaxies. However, their structure is poorly defined by existng observational data. This study was an attempt to gather specific structural information about the disks in Algol-type binary systems. In Algol-type binaries mass transfer ...
Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosity and tidal angular momentum loss. ...
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Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosi...
Too hot accretion disks in ULX and superluminal jet sources ... Standard accretion disk around Kerr black hole can explain the hard disk spectra? ...
As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's ...
Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in ...
About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the ...
Gas giant planets undoubtedly form from the orbiting gas and dust disks commonly observed around young stars, and there are two principal mechanisms proposed for how this may occur. The core accretion plus gas capture model argues that a solid core forms first and then accretes gas from the ...
We present radiation hydrodynamics simulations of the collapse of massive pre-stellar cores. We treat frequency dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, it is possible for the first time to simulate the whole accretion ...
We present fully self-consistent calculations of the spectra emitted by accretion disks in active galactic nuclei. We treat the inner, radiation-pressure-dominated regions of standard alpha-disks. Incoherent Compton scattering and emission/absorption of radiation by hydrogen and helium are included in compting the vertical temperature ...
We investigate the properties and evolution of accretion tori formed after the coalescence of two compact objects. At these extreme densities and temperatures, the accreting torus is cooled mainly by neutrino emission produced primarily by electron and positron capture on nucleons (?-reactions). We solve for the ...
The mass acquired by a gas giant planet has long been believed to result from accretion of material within the surrounding gaseous disk (nebula). Bate, D'Angelo, and I have analyzed the properties and consequences of this flow by means of three-dimensional hydrodynamical simulations. Most of the accretion occurs after the planet has ...
It is plausible that an accretion disk pumps energy into an outer tenuous layer of its atmosphere to form a high-tmeperature corona analogous to the solar corona. General features of such a corona, not specific to any model, are discussed, and order-of-magnitude estimates are made for the physical parameters of a corona on the Cygnus ...
The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the ...
The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of {approx}>3 AU forms prior to the ...
The coagulation and transportation of grains in a turbulent accretion solar nebula has been numerically studied. Compared with the case of a laminar nebula, the turbulence enhances the growth rate. The grains diffuse radially through the nebula owing to turbulent diffusion. The accreted interstellar grains form the reservoir, from ...
We present the first numerical result of fully general relativistic axisymmetric simulations for the collapse of a rotating high-entropy stellar core to a black hole and an accretion disk. The simulations are performed taking into account the relevant microphysics. We adopt as initial conditions a spherical core with constant electron fraction (Ye = 0.5) ...
The understanding of accretion processes and specifically of massive accretion disks is considered the holy grail in high-mass star formation. We propose to study the recently identified massive accretion disk candidate IRAS18089-1732 at high angular resolution (<0.7'') in the highly excited ...
Pulsars with pulsation periods in the millisecond range are thought to be neutron stars that have acquired an extraordinarily short spin period through the accretion of stellar material spiraling down onto the neutron star from a nearby companion. Nearly all the angular momentum and most of the mass of the companion star is transferred to the neutron star. During this process, ...
The dynamical and radiative consequences of disk accretion onto magnetic T Tauri stars (TTS) are examined using the Ghosh and Lamb model. It is shown that a prolonged disk accretion phase is compatible with the low rotation rates measured in these stars if they possess a kilogauss strength field that disrupts the ...
The ubiquity of accretion disks around pre-main sequence and young main sequence stars having the potential to form planetary systems is now well established. However, unknown is an accurate estimate of the fraction of single stars with disks that have pr...
We studied the disk emission component hidden in the single-peaked broad emission lines (BELs) of active galactic nuclei (AGN) using a two-component model. We assumed that the broad lines are formed in an accretion disk plus a surrounding non-disk region, with isotropic cloud velocities. To ...
I calculate the specific angular momentum of mass accreted by a binary system embedded in the dense wind of a mass losing asymptotic giant branch star. The accretion flow is of the Bondi-Hoyle-Lyttleton type. For most of the relevant parameters space the flow is basically an isothermal high Mach number accretion flow. I find that when ...
The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars ...
Recently, Ida et al. made an N-body simulation of lunar accretion from a protolunar disk formed by a giant impact. One of their important conclusions is that the accretion time of the Moon is as short as one month. Such rapid accretion is a necessary consequence of the high surface density of a ...
Circumstellar disks are a natural outcome of the star formation process and the sites where planets form. Gas, mainly hydrogen and helium, accounts for about 99% of the disk's initial mass while dust, in the form of submicron-sized grains, only for about 1%. In the process of forming planets ...
rotating star sweeps through the inner disk region, allowing matter to accrete only ... how and where planets form, and what their masses and atmospheres are. ... Such simulations have yet to achieve full realism, but already provide ...
Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developmen...
University Observatory. The work is being funded jointly by DOE, NSF, and NASA. "The Earth must have an accretion disk is formed, which consists of matter losing it angular momentum and swirling into the core. The inner cylinder has a radius of 7 centimeters and is made of steel, and the outer cylinder has a radius
This project investigates the origin of giant planets, both in the Solar System and around other stars. It is assumed that the planets form by the core accretion process: small solid particles in a disk surrounding a young star gradually coagulate into ob...
In the standard model of gas giant planet formation, a large solid core (~10 times the Earth's mass) forms first, then accretes its massive envelope (100 or more Earth masses) of gas. However, inward planet migration due to gravitational interaction with the protostellar gas disk poses a difficulty in this model. Core-sized bodies ...
We consider the effect of density distribution evolution on the global one-armed oscillation modes in disks around Be stars. Previous studies of global oscillations in Be disks assumed a power-law density distribution of the disk. However, observational results show that some Be stars exhibit evidence of formation and dissipation of ...
We study the formation of a giant gas planet by the core-accretion gas-capture process, with numerical simulations, under the assumption that the planetary core forms in the center of an anti-cyclonic vortex. The presence of the vortex concentrates particles of centimeter to meter size from the surrounding disk, and speeds up the core ...
Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here, we show that the subset of accreting transitional disks with wide, optically thin inner ...
Thermal conduction between a cool accretion disk and a hot inner corona can result in either evaporation of the disk or condensation of the hot corona. At low mass accretion rates, evaporation dominates and can completely remove the inner disk. At higher mass accretion ...
We use two-dimensional hydrodynamic simulations of viscous disks to examine whether dynamically interacting multiple giant planets can explain the large gaps (spanning over one order of magnitude in radius) inferred for the transitional and pre-transitional disks around T Tauri stars. In the absence of inner disk dust depletion, we ...
Jul 20, 2009... protoplanetary disks, radiative transfer, T-TAURI DISKS, ACCRETION DISKS, YOUNG OBJECTS, CIRCUMSTELLAR DISKS, STARS, GROWTH, EARTH, DUST ...
... studies to, eg, measure inner disk truncation radii, probe the nature of the disk accretion process, and chart the evolution in the gas content of disks. ...
Various papers on accretion disks (ADs) and magnetic fields in astrophysics are presented. Individual topics addressed include: relevance of magnetic fields to stars and ADs, nonlinear breakup of the sun's toroidal field, accretion and particle acceleration by spiral shock wages, MHD flows in ADs and jets, slender flux tubes in ADs, ...
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster pres...
The main physical phenomena which occur on accretion disks, are discussed. A numerical simulation of a three dimensional accretion disk model around a white dwarf in a binary system composed of two equal mass stars is developed. The smoothed particle hydr...
With the discovery that Alfven waves can be strongly unstable in a magnetized accretion disk, it can be expected to explain the turbulence necessary to drive accretion in these disks. The instability of non-axisymmetric Alfven waves is studied using analy...
Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized obje...
The influence of accretion disk instabilities on the UV fluxes of Seyfert 1 galaxies was studied. The observed characteristic timescales of variability are consistent with the interpretation that most of the UV radiation originates in an accretion disk, a...
The astrophysical importance of the new class of theoretical models for accretion disks concentrating mainly on the applications to active galactic nuclei are discussed. The slim accretion disks model describes several important astrophysical processes wh...
We examine the role of the accretion disk in the steady-burning white dwarf model for supersoft sources. The accretion luminosity of the disk is quite small compared to the nuclear burning luminosity of the central source. Thus, in contrast to standard ac...
Mar 12, 2005 ... Accretion Disk Simulation Credit: Michael Owen, John Blondin ... Such accretion disks power bright x-ray sources within our own galaxy. ...
We present an update on our ongoing project to characterize a large sample of Spitzer selected transition disks located in several star-forming regions. Transition objects are pre-main-sequence stars with optically thin inner disks and optically thick outer disks. Different mechanisms have been proposed to explain ...
Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find that radiation ...
We have constructed models of stars which form by accretion from a disk. We have calculated accretion and pre-main-sequence evolutionary tracks for a range of initial parameters which spans the physically reasonable modes for accretion. We find that these models agree with the observed ...
Recent infrared observations of molecular lines by the Spitzer Space Telescope have revealed the chemical properties in the surface layers of planet-forming regions in protoplanetary disks. These observations, together with (sub)millimetre molecular line observations, are useful tools for diagnosing the physical and chemical properties of ...
We find a dimming during optical quiescence of the cataclysmic variable WZ Sge by about half a magnitude between superoutbursts. We connect the dimming with the development of a cavity in the inner part of the accretion disk. We suggest that, when the cavity is big enough, accretion of material is governed by the magnetic field of the ...
The formation of low mass stars takes place with the assistance of an accretion disk that transports gas and dust from the envelope of the system to the star, and a jet that removes angular momentum and allows accretion to proceed. In the radio, these ionized jets can be studied very close to the star via the thermal (free-free) ...
The authors suggest that a rotating massive black hole (105Msun) located at an inactive galaxy may convert its host into a transient active phase by capturing and disrupting a star. During this period, a transient accretion disk is formed and a strong transient magnetic field can be produced in the inner boundary of the ...
We present radiation hydrodynamic simulations of the collapse of massive pre-stellar cores. We treat frequency-dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, for the first time it is possible to simulate the whole accretion ...
Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...
... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...
... unique opportunities to study the details of the accretion flow in the cases of normal white dwarfs with accretion disks and magnetic white dwarfs. ...
Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding
We use cosmological smoothed particle hydrodynamic simulations to study the kinematic signatures of cool gas accretion onto a pair of well-resolved galaxy halos. We find that cold-flow streams and gas-rich mergers produce a circumgalactic component of cool gas that generally orbits with high angular momentum about the galaxy halo before falling in to build the ...
Aperiodic fluctuations with 1/f-like power spectral density (PSD, where f is a frequency) are characteristics of X-ray radiation from accreting compact objects, such as active galactic nuclei and Cyg X-1. To account for such intriguing features, we previously proposed a cellular-automaton model for accretion disks based on the concept ...
A simple model of gas accretion in young galaxy disks suggests that fast turbulent motions can be driven by accretion energy for a time t{sub acc} {approx} 2(epsilon{sup 0.5} GM {sup 2}/xiV {sup 3}){sup 0.5} where epsilon is the fraction of the accretion energy going into disk turbulence, M and ...
How are accretion disks in Seyfert Galaxies oriented relative to the disk of the spiral galaxy which hosts them? This angle, ?, serves as a link between the innermost workings of the black hole plus fueling accretion disk and the larger galaxy, either as the memory of the activity-provoking ...
We revisit our original papers on the burst mode of accretion by incorporating a detailed energy balance equation into a thin-disk model for the formation and evolution of circumstellar disks around low-mass protostars. Our model includes the effect of radiative cooling, viscous and shock heating, and heating due to stellar and ...
The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based
The standard model of an accretion disk is considered. The temperature in the inner region is computed. It is assumed that the radiated power derives from comptonized photons, produced in a homogeneous single temperature plasma, supported by radiation pre...
Jan 22, 2011 ... Title: The Production of Jets From Magnetized Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, D. ...
Jan 22, 2011 ... Title: The Production of Jets From Magnetic Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, David L. ...
of a collimated jet ejected from the center of the accretion disk. The jet velocity is a strong function of the strength of the initial magnetic field: ...
The standard model for accretion disks (e.g., Pringle, 1981; Lin and Papaloizou, 1985) parameterizes
Feb 23, 2004 ... "Accretion disks are known to flow around many objects in the universe ... Under normal conditions, accretion disks appear far too minute to ...
Jan 31, 2005 ... KERRBB is a multi-temperature blackbody model for a thin, steady state, general relativistic accretion disk around a Kerr black hole. ...
The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical ...
First � Previous � Next � Last � Index � Home � Text. Long-term Periodicities and Accretion Disks. Slide 4 of 22.
Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...
... Title : Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri. ...
Jun 11, 2010 ... Relativistic Illumination Law from Accretion Disks ... Relativistic Iron Fluorescent Line from Accretion Disks ...
Quasar Jets and Accretion Disks. Questions: " Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? ...
Binary Black Holes, Accretion Disks and Relativistic. Jets: Photocenters of Nearby AGN and Quasars. Principal Investigator: Ann E. Wehrle (Interferometry ...
Accretion Disk Coronae were first suggested to explain the incomplete eclipses and shallow profiles observed from some Low Mass X-ray Binaries (White and ...
Dec 19, 1999 ... Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. ...
Sep 4, 1998 ... In the case of a HMXB with a large ( $\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\ ) magnetic field the accretion disk cannot extend all the way down to ...
Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk ...
