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 ...

Calculations of the velocity field in an accretion disk show that matter may flow in the disk not only toward but also away from the central object. The rates of flow are determined, and the geometry of hydrodynamic motions in nonstationary disks is discussed.

... 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. ...

Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is

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 ...

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 ...

We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin

We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretion flows with large mass ...

Recent observational data has shown that the Algol-type binary system RS Vul possesses an accretion disk tilted out of the orbital plane. Magnetic effects in the surface of the donor star could produce a nontrivial effect in the flow of the accretion stream as it travels through the L1 Lagrange point. Such a ...

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 ...

An approximation theory of the acceleration of particles in low-density shear flows is developed and is applied to a number of astrophysical flows including accretion disks, radial accretion, and convective turbulence. In the disk application, the theory suggests a ...

Oct 3, 2006 ... This is an X-ray spectral model from optically-thick Advection Dominant Accretion Flow, often called "slim disk", which is expected when the ...

This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magne...

A unified theory of active galactic nuclei, based on the physics of accretion flows around massive black holes, is described. The accretion modes are dependent on the ratio of accretion rate to the mass of the hole. The spectral characteristics and radiative efficiency for the ion tori, thin ...

accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...

The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the ...

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 ...

ionized dead zone containing a smooth field that drives a residual flow of gas toward the young star. http://www.jpl.nasa.gov/ ...

We discuss the effect of the Poynting flux on a magnetically dominated thin accretion disk, which is simplified to a two-dimensional disk on the equatorial plane. It is shown in the relativistic formulation that the Poynting flux caused by a rotating magnetic field with Keplerian angular velocity can balance the energy and angular ...

HD101088 is a young binary accreting from a tenuous circumprimary and/or circumsecondary disk despite the apparent lack of a massive dusty circumbinary disk. We propose to observe it with RGS with an exposure of 60 ks to detect the emission lines from the O VII He-like ion and look for potential high-density plasma at the base of the ...

We discuss the dynamics of the accretion flow onto a black hole driven by Poynting flux in a simplified model of a two-dimensional accretion disk. In this simplified model, the condition of the stationary accretion flow is found to impose a nontrivial constraint on the ...

Recent work on a unified model of accretion flows and X-ray emission in low mass X-ray binaries is summarized. In this model, a weakly magnetic neutron star accretes gas simultaneously from a Keplerian disk and a corona above the inner part of the disk. P...

We have found an isolated polar disk galaxy in what appears to be a cosmological wall situated between two voids. This void galaxy is unique as its polar disk was discovered serendipitously in an H I survey of SDSS void galaxies, with no optical counterpart to the H I polar disk. Yet the H I mass in the disk is ...

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

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 ...

We investigate the model of disk/coronal accretion into a black hole. We show that the inner regions of an accretion disk in X-ray binaries can transform from a cool standard disk to an advection-dominated flow through the known properties of Coulomb interaction in a ...

We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied ...

Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary ...

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 ...

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 ...

A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction ..beta..approx.10/sup -2/ to 10/sup -3/ of the ...

The authors examine the possibility of neutron viscosity as the mechanism responsible for the dissipation of kinetic energy into luminosity in the innermost parts (r < 100 R sub s) of accretion disks surrounding compact objects. They present simplified models of such self-consistent, steady state accretion flows ...

Dec 10, 2009 ... "Suzaku's sensitivity to iron emission lines and its ability to measure the ... confirms the presence of low-density accretion flow in these systems. ...

Apr 20, 2009... ADVECTION-DOMINATED ACCRETION, ENERGY EXTRACTION, GRO J1655-40, BINARIES, PRECESSION, DISCOVERY, MODELS, PLASMA, FLOWS, DISK ...

Mar 1, 2011 ... Author: Knight, J. W., III. Abstract: An idealized steady state model .... uniform, vertical magnetic field. The accretion flow in the disk ...

Active galactic nuclei (AGN) are powered by accretion and recent observations indicate the existence of accretion disks around a central black hole of 108 to 1010Msun. A derivation and discussion of the basic equations for the structure of a thin accretion disk around a rotating black hole is ...

Hydrodynamical winds from hot accretion disks around compact objects are investigated using a simplified model. The flow pattern above the disk is solved assuming that specific angular momentum is conserved along a stream line and that the radial component of the gravitational force balances the centrifugal force ...

The investigations of advection-dominated accretion flows (ADAFs), with emphasis on applications to X-ray binaries containing black holes and neutron stars is presented. This work is now being recognized as the standard paradigm for understanding the vari...

The existence of accretion disks around young stellar objects has recently become widely accepted. The luminosity of some young stellar objects is highly variable and is generally attributed to the release of gravitational energy from matter funneled onto them by accretion disks. The inward transport of matter ...

The literature is full of a large number of accretion flow models, each of which claims to be the correct one. We present here the most general possible flow configuration around a black hole, different regions of which have characteristics of different models such as the Bondi flow, the Keplerian ...

We propose an eclipsing light-curve diagnosis for black-hole accretion flows. When emission from an inner accretion disk around a black hole is occulted by a companion star, the observed light curve becomes asymmetric at ingress and egress on a time scale of 0.1-1seconds. This light-curve analysis provides a means ...

The transport of angular momentum in the outward direction is the fundamental requirement for accretion to proceed in an accretion disk. This objective can be achieved if the accretion flow is turbulent. Instabilities are one of the sources for the turbulence. We study a differentially rotating ...

Consideration is given to the effects of thermal and nonthermal electron-positron pair production upon the structure of two-temperature accretion disks and upon the two-temperature criterion in quasi-spherical accretion flows, by balancing pair creation with annihilation and inflow. It is found that thermal pair ...

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 ...

Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{&sun;} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk ...

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 ...

Differentially rotating disks are subject to the axisymmetric instability for perfectly conducting plasma in the presence of poloidal magnetic fields. For nonaxisymmetric perturbations, the authors find localized unstable eigenmodes whose eigenfunction is...

Jan 15, 1997 ... Black Holes Signature From Advective Disks ... however, has provided a new way to tell them apart: advective accretion flows (ADAFs). ...

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 ...

To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (r?phi) to obtain the explicit structure along the ?-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential ...

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 ...

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 ...

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 ...

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, ...

The authors present a model for the high-low state transition of the X-ray Nova GS 1124-68 (Nova Muscae 1991) observed by Ginga. The model consists of an advection-dominated accretion flow (ADAF) near the central black hole surrounded by a thin accretion disk. During the rise phase of the outburst, as the mass ...

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 ...

Black holes are most often detected by the radiation produced when they gravitationally pull in surrounding gas, in a process called accretion. The efficiency with which the hot gas radiates its thermal energy strongly influences the geometry and dynamics of the accretion flow. Both radiatively efficient thin disks ...

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

The observed iron K{alpha} fluorescence lines in Seyfert I galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the line emission. These lines serve as powerful probes for examining the structure of inner regions of accretion disks. Previous studies of line emission ...

The first VLBI images of H2O maser emission in the Circinus Galaxy AGN show both an accretion disk and outflow 0.1 to 1 pc from the central engine. The maser traces a warped, edge-on accretion disk between radii of about 0.1 and 0.4 pc that is bound by a 1.3�106 Msolar central mass. The rotation curve is somewhat ...

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 ...

A possible accretion model associated with the ionization instability of quasar disks is proposed to

We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then ...

The shape of the Alfven surface separating the magnetosphere of a neutron star from the stream of accreting plasma and the velocity and scattering optical depth of the gas layer flowing along the Alfven surface are calculated. Calculations are made both for spherically symmetrical fall of the gas and for disk ...

Accretion disks around (supermassive) black holes act as "machines" which extract gravitational energy. In fact, the observed radiation allows to sample the physical conditions very close to the event horizon. For a test particle, the innermost stable circular orbit (ISCO) is located at 3 rS for a non-rotating hole (Schwarzschild metrics; at smaller radii ...

The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular ...

The standard massive accretion disk with Keplerian angular momentum (standard accretion disk) producing gamma-ray bursts (GRBs) is investigated on the bases of the microphysics of neutrinos and general relativity. Since the accretion disk gradually heated by viscosity is ...

The standard massive accretion disk with Keplerian angular momentum (standard accretion disk) producing gamma-ray bursts (GRBs) is investigated on the bases of the microphysics of neutrinos and general relativity. Since the accretion disk gradually heated by viscosity is ...

Abstract. The accretion process onto a magnetized isolated neutron star, which captures material from the interstellar medium, is discussed. The evolutionary track of such a star can be presented as a sequence of four states: ejector, supersonic propeller, subsonic propeller, andsteady accretor. Ishowthatsubsonic propeller ? accretor transition does not occur as long as the ...

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, ...

Angular momentum transport by photons is analyzed for thin and thick configurations of steady accretion flows near black holes. The radiative viscosity coefficient is derived accurately from kinetic theory for arbitrary photon spectra. Thin Keplerian disks cannot be supported by radiative viscosity. However, in a quasi-spherical ...

The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle. Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity. Hence, any viscosity in such systems must be due to ...

We have constructed vertically integrated, steady state convective models of accretion disks to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick and the resulting convective structure ...

Vertically integrated, steady state convective models of accretion disks have been constructed to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick, and the resulting convective ...

Hyperaccreting neutron stars or magnetar disks cooled via neutrino emission can be candidates of gamma-ray burst (GRB) central engines. The strong field >=1015-1016 G of a magnetar can play a significant role in affecting the disk properties and even lead to the funnel accretion process. In this paper, we investigate the effects of ...

Hyperaccreting neutron stars or magnetar disks cooled via neutrino emission can be candidates of gamma-ray burst (GRB) central engines. The strong field {>=}10{sup 15}-10{sup 16} G of a magnetar can play a significant role in affecting the disk properties and even lead to the funnel accretion process. In this paper, we ...

The formation and evolution of an accretion disk formed during the collapse of a rotating cloud core

We outline recent progress in understanding the accretion of plasma to rotating magnetized stars obtained from global axisymmetric (2D) and 3D magnetohydrodynamic (MHD) simulations in three main areas: (1.) Formation of jets from disk accretion onto rotating magnetized stars: From simulations where the viscosity and magnetic ...

The results of nonrelativistic radiation-hydrodynamic calculations of axisymmetric supercritical accretion disks around Newtonian quasi-black holes are reported. Anisotropic and isotropic constant kinematic viscosity models are used, with radiation transport described by a gray Thomson scattering opacity and flux-limited diffusion. The resulting solutions ...

We study the effect of radiation pressure on the dust in the inner rim of transitional disks with large inner holes. In particular, we evaluate whether radiation pressure can be responsible for keeping the inner holes dust-free, while allowing gas accretion to proceed. This has been proposed in a paper by Chiang & Murray-Clay (2007, Nature Phys., 3, ...

The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based on the disk instability model. The thermal transition of the outer portions of the disk controls the mass flow rate into the inner portions of the disk, thus modulating the ...

Whether the existence of cold accretion disks around isolated, magnetized neutron stars might result in a distinct observational signature due to the Compton drag interaction between the electrostatically accelerated changes and the thermal radiation emitted by these disks. The particle dynamics resulting from the combined effects of ...

Observations of star formation and kinematics in early galaxies at high spatial and spectral resolution have shown that two-thirds are massive rotating disk galaxies, with the remainder being less massive non-rotating objects. The line-of-sight-averaged velocity dispersions are typically five times higher than in today's disk galaxies. This suggests that ...

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...

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 ...

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 ...

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions ...

A new computational scheme is developed to study gas accretion from a circumbinary disk. The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it. This scheme enables us to solve the centrifugal balance of a gas disk against gravity with ...

A new computational scheme is developed to study gas accretion from a circumbinary disk. The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it. This scheme enables us to solve the centrifugal balance of a gas disk against gravity with ...

290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...

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 ...

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 ...

Optical spectroscopy of the nova-like variable V1315 Aql shows strong single-peaked emission lines, high-velocity s-waves in the wings of the lines, and two distinct absorption components. In order to explain all the features, I suggest that disk overflow accretion has to be combined with an accretion disk wind. ...

The stability and evolution of windy accretion disks is investigated in detail. The basic disk evolution equations are briefly recapitulated, and an idealized analytic treatment of the wind and viscosity is used to show that steady disk flow is indeed unstable for sufficiently large ratio of ...

Recent observations of stellar-mass black holes have revealed evidence of black hole spin, disk winds, and aspects of how accretion flows vary with the mass accretion rate. We propose to build on these successes with a single 40 ksec (total) observation of a black hole transient in outburst. Though modest, this ...

OAK-B135 We consider an accretion flow model originally proposed by Bisnovatyi-Kogan and Ruzmaikin (1974), which has been confirmed in recent 3D MHD simulations. In this model, the accreting gas drags in a strong poloidal magnetic field to the center such that the accumulated field disrupts the axisymmetric ...

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. ...

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? ...

Mass accretion onto (proto-)stars at high accretion rates M-dot{sub *}> 10{sup -4} M{sub sun} yr{sup -1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk ...

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 ...

The warped spacetime near black holes is one of the most exotic observable environments in the Universe. X-ray spectra from active galaxies obtained with the current generation of X-ray observatories reveal line emission that is modified by both special relativistic and general relativistic effects. The interpretation is that we are witnessing X-ray irradiated matter orbiting in an ...

Aims. We investigate the accretion process from an accretion disk onto a magnetized rotating star with a purely dipolar magnetic field. Our main aim is to study the mechanisms that regulate the stellar angular momentum. In this work, we consider two effects that can contrast with the spin-up torque normally associated with ...

Accretion disks are three-dimensional, turbulent, often self-gravitating, magnetohydrodynamic (MHD) flows, which can be modeled with numerical simulations. In this paper, we present a new algorithm that is based on a spectral decomposition method to simulate such flows. Because of the high order of the method, we ...

We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, ?0, we can reproduce three distinct modes of ...

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 most energetic phenomena in the universe are systems powered by gravity through accretion. For compact stars such as white dwarfs, neutron stars, and especially black holes, the energy released per unit mass accreted can significantly exceed that released by nuclear reactions. Over the last half century a growing body of observations has revealed a ...

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial ...

Context. The number of strong iron K? line detections in Seyfert AGN is clearly growing in the Chandra, XMM-Newton and Suzaku era. The iron emission lines are broad, some are relativistically blurred. These relativistic disk lines have also been observed for galactic black hole X-ray binaries. Thermal components found in hard spectra were interpreted as an indication for a ...

Black hole XRB X-ray variability contains information about the accretion and emission mechanisms in strong gravity, but to unlock this information and understand the very rich phenomenology of X-ray timing properties (band-limited noise, QPOs, low-frequency noise), we need to understand the origin of the variations. For many years it has been assumed that the Lorentzian ...

A numerical investigation is made of the evolution of the preplanetary disk to the accretion stage of collapse of the protosolar nebula, with an angular momentum of (1-2) x 10/sup 52/ g x cm/sup 2//sec, with allowance for the accretion of material onto the disk. It is shown that during moderate subsonic ...

The magnetorotational instability (MRI) is the most likely candidate for angular momentum transport and radial flow of mass in protoplanetary disks (PPDs), but demands a minimum ionization fraction for the gas to couple to the magnetic field. It is known that large regions of PPDs are insufficiently ionized for the MRI to act, and are �dead zones.� ...

We discuss results of 2D and 3D numerical simulations of gas accretion processes in binary stars of the T Tau type. Analysis of the obtained flow structure shows that in such systems following gas dynamic details are formed: inner gap, circumstellar disks, bow shocks before components, and gaseous ``bridge'' between the components. It ...

Spectra in outburst sources are found to become soft in viscous timescales before going back to hard as in the pre-outburst phase. By using two component accretion disks we show that major characteristics of the spectral evolution can be reproduced. We find that the outburst is possibly caused by a sudden rise in viscosity which gradually converts the ...

We compute the resultant spectrum due to multiple scattering of soft photons emitted from a Keplerian disk by thermal electrons inside a torus axisymmetrically placed around a black hole. In a two component advective flow model, the post-shock region is similar to a thick accretion disk and the pre-shock ...

We compute the resultant spectrum due to multiple scattering of soft photons emitted from a Keplerian disk by thermal electrons inside a torus axisymmetrically placed around a black hole. In a two component advective flow model, the post-shock region is similar to a thick accretion disk and the pre-shock ...

The inner accretion disk geometry of black hole binaries (BHBs) in transition between the low/hard and high/soft states is important for understanding accretion flow around black holes. In the low/hard state a discrepancy exists over whether the cool, optically thick accretion ...

We present new thermal equilibrium solutions for optically thin and optically thick disks incorporating magnetic fields. The purpose of this paper is to explain the bright hard state and the bright/slow transition observed in the rising phases of outbursts in black hole candidates. On the basis of the results of three-dimensional magnetohydrodynamic simulations, we assume that ...

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 holes of 15 AU or ...

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 ...

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 ...

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 surrounding disk once ...

Understanding the evolution of gas and dust within protoplanetary disks is important for planet formation, for modeling astronomical observations of disks, and for interpreting mineralogical constraints on the Solar Nebula. The gas and solid components undergo distinct physical processes, but their evolution is coupled by aerodynamic forces whose strength ...

It seems to be a widely accepted opinion that the types of accretion disks (or flows) generally realized in the nuclei of radio galaxies and in further lower mass-accretion rate nuclei are inner, hot, optically thin, radiatively inefficient accretion flows (RIAFs) ...

The energetics of a ..gamma..-ray burster can be explained by the rapid accretion of > or approx. =10/sup 19/ g of matter onto a neutron star surface. It is proposed that this sudden infall of matter may be the result of a radiation-driven instability which occurs at the boundary between an accretion disk and the surface of a slowly ...

We present new insights about accretion and ejection physics based on joint RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the first time, with fast phase-resolved spectroscopy of the ? state, we are able to show that changes in the broadband X-ray spectrum (RXTE) on timescales of seconds are associated with measurable changes in absorption lines ...

Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1) a small-scale turbulent magnetic field in the disk (due to the magnetorotational instability, MRI), which gives a large viscosity enhancing accretion, and (2) a large-scale magnetic field, ...

Angular momentum transport by photons is analyzed for thin and thick configurations of steady accretion flows near black holes. The radiative viscosity coefficient is derived accurately from kinetic theory for arbitrary photon spectra. Thin Keplerian disks cannot be supported by radiative viscosity. However, in a quasi-spherical ...

. #12; "Superluminal" motion: an optical illusion Motion along the line of sight accounts for the apparent velocity"). #12; AGN in the optical Highenergy photons emerging from an AGN accretion flow (typically, an accretion disk) can ionize atoms in the surrounding gas. Optically bright AGN are identified as Seyfert ...

years of observations. #12; "Superluminal" motion: an optical illusion Motion along the line of sight...] "AGNs"). #12; AGN in the optical Highenergy photons emerging from an AGN accretion flow (typically, an accretion disk) can ionize atoms in the surrounding gas. Optically bright AGN are identified as Seyfert

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. ...

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 will observe soft X-ray transients (SXTs) as targets of opportunity using the FOS at UV wavelengths. This is part of an extensive multiwavelength campaign to monitor newly discovered SXTs in outburst and throughout the subsequent decline. Recent work establishes that a high proportion of SXTs harbor black holes, so these observations provide an unrivalled opportunity to obtain high quality data ...

Low-mass X-ray binaries (LMXBs) are systems in which a low-mass companion transfers mass via Roche-lobe overflow onto a black hole (BH) or a weakly magnetized neutron star (NS). It is believed that both the solid surface and the magnetic field of an NS can affect the accretion flow and show some observable effects. Using the disk ...

We invesgitage the interaction between the stellar magnetic field and the accreting plasma at the magnetospheric boundary of a neutron star accreting matter from a disk. The stellar magnetic field penetrates the inner part of the disk via the Kelvin-Helmholtz instability, turbulent diffusion, and reconnection, ...

Simultaneous multiwavelength observations were recently performed for three black hole candidates�SWIFT J1753.5-0127, GRO J1655-40, and XTE J1720-318. In this paper, we test the accretion-jet model originally proposed for XTE J1118+480 by investigating the hard state of these three sources using this model. The accretion flow in the ...

The accretion of hot slowly rotating gas onto a supermassive black hole is considered. Rotation velocities at the Bondi radius r_B are small in comparison with speed of sound c_s. The centrifugal barrier at a depth r_c = l^2/G M_BH << r_B hinders supersonic accretion. We take into account saturated electron thermal conductivity and Bremsstrahlung ...

Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...

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 ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

A possible accretion model associated with the ionization instability of quasar disks is proposed to

We present a "combined" model taking into account visual manifestations of the interaction between the gas flow and the accretion disk in a close binary system in the form of a "hot line" and a "hot spot." The binary consists of a red dwarf that fills its Roche lobe and a compact spherical star (a white dwarf or neutron star) ...

In two previous publications, we have demonstrated that stationary rotation of magnetized plasma about a compact central object permits an enormous number of different MHD instabilities, with the well-known magneto-rotational instability as just one of them. We here concentrate on the new instabilities found that are driven by transonic transitions of the poloidal flow. A ...

We study the process of spinning up black holes by accretion from slim disks for a wide range of accretion rates. We show that for super-Eddington accretion rates and low values of the viscosity parameter ? ( ? 0.01) the limiting value of the dimensionless spin parameter a? can reach values higher than a? = 0.9978 ...

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 ...

Recent observations and theoretical work on gamma-ray bursts favor the central engine model of a Kerr black hole (BH) surrounded by a magnetized neutrino-dominated accretion flow (NDAF). The magnetic coupling between the BH and the disk through a large-scale closed magnetic field exerts a torque on the disk 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: ...

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 ...

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 ...

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 ...