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 ...
NASA Website
Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many
NASA Technical Reports Server (NTRS)
Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...
Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,
A model of the X-ray radiation emitted from the accretion column of a compact object in AM Herculis binaries, using Monte Carlo methods is presented. The accretion column in the model has cylindrical symmetry. Above a shocked region in the column there is...
National Technical Information Service (NTIS)
A likely process for energy production of quasars is the release of gravitational energy from matter accretion onto a compact and massive object. One of the possible configurations is a thin accretion disk around a massive black hole (10(exp 8) to 10(exp ...
The inverse problem of interpreting the SS 433 optical light curves is solved for a geometrically thick model accretion disk around the compact relativistic object: most likely a black hole.
Energy Citations Database
Encapsulated atop the vehicle is the X-ray Timing Explorer (XTE), which the Delta ... The accreting gas can be guided to the magnetic pole of the compact object ...
Accreting compact object; Eddington-limited outbursts (rise of days; duration of weeks; recurrence of decades); Superluminal jets; Quiescent light dominated ...
We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the centr...
The broadened iron lines observed from accreting compact objects are most easily interpreted in terms of reflection onto the accretion disc of the hard X-ray photons emitted by the central source. In this context, such a broadness is due to the relativistic motion of the reflecting plasma, in the deep gravitational ...
NASA Astrophysics Data System (ADS)
Bright pulsating X-ray sources (X-ray pulsars, AM Her stars,...) have been identified as strongly magnetized compact objects accreting matter from a binary companion. We give here a summary of some of the work which has been recently done to try to unders...
We consider a model in which massive stars form in a self-gravitating accretion disk around an active galactic nucleus (AGN). These stars may evolve and collapse to form compact objects on a time scale shorter than the accretion time, thus producing an important family of sources for LISA. Assuming 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 ...
The contents include: Star deaths and the formation of compact objects; White dwarfs; Rotation and magnetic fields; Cold equation of state above neutron drip; Pulsars; Accretion onto black holes; Supermassive stars and black holes; Appendices; and Indexes. This book discusses one aspect, compact ...
It has been clear for many years now that the process of accretion on to a compact object is largely dominated by magnetic fields. The magnetic field channels the accretion flow onto strongly magnetized stars such as magnetic white dwarfs (cataclysmic variables), and neutron stars (accreting ...
The collapse of massive molecular clumps can produce high mass stars, but the evolution is not simply a scaled-up version of low mass star formation. Outflows and radiative effects strongly hinder the formation of massive stars via accretion. A necessary condition for accretion growth of a hydrostatic object up to high masses M > ...
Context. The Galactic microquasar SS 433 is very luminous and ejects opposite jets at approximately one quarter the speed of light. It is regarded as a super-Eddington accretor but until recently there were no observations of accretion. Aims: We present an analysis of spectroscopic optical data obtained before and during a major flare, which yield in H? unambiguous evidence ...
The detection of fast quasi-periodic variability from accreting black holes and neutron stars has been used to constrain their masses, radii, and spins. If the observed oscillations are linear modes in the accretion disks, then bounds can be placed on the properties of the central objects by assuming that these modes are locally ...
Optically thin accretion disks with bremsstrahlung are calculated in the bimetric theory of gravitation. The obtained results are compared with the corresponding results in Einstein's theory. The gravitational sensitivity of the inner disk edge, situated in the strong field of a central compact object, is an argument in ...
The prime scientific objectives of the Rossi X-Ray Timing Explorer (RXTE) were the study of astrophysical compact objects: black holes (galactic and extragalactic), many types of neutron stars, and accreting white dwarfs. RXTE was successful in achieving ...
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was
Analytic methods show stability of the stationary accretion of test fluids but they are inconclusive in the case of self-gravitating stationary flows. We investigate numerically stability of those stationary flows onto compact objects that are trans-sonic and rich in gas. In all studied examples solutions appear stable. Numerical ...
accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...
We show that a moderately massive disk (10/sup -5/--10/sup -2/ M/sub sun/) can cause the Lense-Thirring precession of the compact object (neutron star or black hole) at its center. The inner regions of the disk (r< or approx. =10/sup 8/ cm) align with the equator of an will precess at the same rate as the compact ...
Accretion onto compact objects plays a central role in high energy astrophysics. In these environments, both general relativistic and plasma effects may have significant impacts upon the spectral and polarimetric properties of the accretion flow. In paper I we presented a fully general relativistic magnetoionic ...
DOE Information Bridge
Accretion is a pervasive process in astrophysics. Through accretion, protostars gather enough mass to initiate fusion, and small bodies gather enough mass to become planets. Accretion onto black holes is the second most efficient physical process presently known, allowing up to 30% of the rest-mass energy of the ...
We study the standing dissipative and non-dissipative shocks and the isentropic compression waves systematically in the thin, rotating, adiabatic astrophysical flows, such as accretion or winds, near the black holes and the neutron stars. The flow is assu...
Matter swirls around the compact object in the accretion disk like water going down the drain. Because a black hole is invisible and a neutron star is so ...
It is stated that the detection of a number of soft gamma -ray bursts by Vela satellites has generated great interest in their possible source. The possibility is considered that the bursts may originate from transient episodes of accretion on to compact galactic objects, such as white dwarfs, neutron stars, or black holes. ...
The accretion process onto spinning objects in Kerr spacetimes is studied with numerical simulations. Our results show that accretion onto compact objects with Kerr parameter (characterizing the spin) |a|<M and |a|>M is very different. In the superspinning case, for |a| moderately ...
We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an exa...
We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surroun...
The Balmer H alpha emission line in the stationary spectrum of SS 433 has a component originating in the wind above the accretion disk. The Doppler motion of this line is a blurred representation of the motion of the compact object accreting. I show how this may be understood in terms of emission lasting over a few ...
E-print Network
We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital ...
An MHD model for the formation of a jet in the vicinity of a compact object with a supersonic accretion regime is constructed, assuming that the plasma is perfectly electrically conducting. A stable, collimated jet of plasma along the z axis symmetric about the plane of the accretion disk is obtained. The ...
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 ...
String theory predicts the existence of extremely compact objects spinning faster than Kerr black holes. The spacetime exterior to such superspinars is described by Kerr naked singularity geometry breaking the black-hole limit on the internal angular momentum. We demonstrate that the conversion of Kerr superspinars into a near-extreme black hole due to an ...
... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...
Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the ...
We consider roughly 106 to 107 solar mass black holes (MBHs) in galactic nuclei. As such objects grow by accretion, some fraction of the accreted mass is in the form of compact stars. If the approach to coalescence proceeds gradually, many orbital revolutions will occur, and substantial amounts of gravitational ...
Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion discs that ...
The dynamics of an axisymmetric stationary disc of accreting magnetofluid with finite conductivity around a rotating compact object is presented here. Along with the Maxwell equations and the generalized Ohm law, the basic equations governing the motion of a finitely conducting plasma in a curved space-time around a slowly rotating ...
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 ...
We discuss the consequences of the accretion of dark matter (DM) particles on compact stars such as white dwarfs and neutron stars. We show that in large regions of the DM parameter space, these objects are sensitive probes of the presence of DM and can be used to set constraints both on the DM density and on the physical properties of ...
Although disk accretion onto compact objects-white dwarfs, neutron stars and black holes-is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially ...
PubMed
We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 Msolar. Supercritical accretion is expected to occur in a supernova (SN) with fallback material accreting onto a nascent compact object. We find ...
Low mass X-ray binaries (LMXBs) are interacting systems in which a neutron star or black hole accretes material from a donor star via an accretion disk. LMXBs provide excellent environments for studying the evolution of compact objects, disk accretion dynamics, and physics in the strong gravity ...
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 everywhere. An ...
Several types of cataclysmic events involving stellar-mass compact objects could result in the extreme, transient accretion onto a black hole widely believed to power gamma-ray bursts. We calculate the vertical structure of such thick accretion disks with a semi-analytical model which includes the effects of ...
Outflowing jets are observed in a variety of astronomical objects such as accreting compact objects from X-ray binaries (XRBs) to active galactic nuclei (AGN), as well as at stellar birth and death. Yet we still do not know exactly what they are comprised of, why and how they form, or their exact relationship ...
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...
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...
Galactic accreting compact objects, such as stellar-mass black holes and neutron stars, can give us a unique perspective into the behavior of matter in extreme conditions. However, the exact nature of accretion onto these objects is not yet well understood. X-ray studies provide us with a means ...
Galactic accreting compact objects, such as stellar-mass black holes and neutron stars can give us a unique perspective into the behavior of matter in extreme conditions. However, the exact nature of accretion onto these objects is not yet well understood. X-ray studies provide us with a means ...
X-ray line emission with several-keV of photon energy was observed from photoionized accreting clouds, for example CYGNUS X-3 and VELA X-1, those are exposed by hard x-ray continuum from the compact objects, such as neutron stars, black holes, or white dwarfs, although accreting clouds are thermally cold. The x-ray ...
With the advent of high resolution X-ray telescopes, the ability to identify extragalactic black holes has greatly enhanced our understanding of massive compact objects, as we are no longer limited to the rather meager Milky Way black hole population. The greatly increased numbers have opened up opportunities to find new modes of ...
We present the results of three-dimensional general relativistic hydrodynamic simulations of adiabatic and spherically symmetric accretion in Kerr space-time. We consider compact objects with spin parameter |a{sub *}|{<=}1 (black holes) and with |a{sub *}|>1 (superspinars). Our full three-dimensional simulations confirm ...
We present the results of three-dimensional general relativistic hydrodynamic simulations of adiabatic and spherically symmetric accretion in Kerr space-time. We consider compact objects with spin parameter |a*|?1 (black holes) and with |a*|>1 (superspinars). Our full three-dimensional simulations confirm the formation of equatorial ...
Detection of gravitational waves from accreting neutron stars (NSs) in our Galaxy, due to ellipticity or internal oscillation, would be a breakthrough in our understanding of compact objects and explain the absence of NSs rotating near the break-up limit. Direct detection, however, poses a formidable challenge. Using the current data ...
Compact binaries have long been a paradigm for accretion theory. Much of our present view of how accretion occurs comes directly from the comparison of theory with observations of these sources. Since theory differs little for other objects such as active galaxies, increasing efforts have recently gone into ...
Possible mechanisms of ..gamma..-ray emission from a neutron star during the accretion of matter onto its surface are discussed. The proposed mechanism of the creation of ..pi../sup 0/ mesons in the collisions of nuclei led to considerable strengthening of the expected ..gamma..-ray emission. Measurement of the spectrum of hard ..gamma.. radiation in the energy range of ...
The x rays emitted by the close binary system ..beta.. Per evidently represent the radiation of a ''hot spot'' on the surface of the Algol A component. This spot is formed by accretion onto Algol A of gas shed by the other component, Algol B. Unlike familiar x-ray sources containing compact objects, ...
We propose a two-component model consisting of a standard thin accretion disk and a hotter corona for 3U 1820--30, with the giant X-ray bursts originating in the inner (radiation-pressure dominated) region of the disk. Arguments in favor of and methods to test such a model are briefly discussed. Parameters of the bursting region are estimated, and an upper limit for the mass ...
We present time-dependent models of the remnant accretion discs created during compact object mergers, focusing on the energy available from accretion at late times and the composition of the disc and its outflows. We calculate the dynamics near the outer edge of the disc, which contains the majority of the disc's ...
Accretion in astrophysical objects and the energetic phenomena it triggers are discussed in reviews and reports of recent theoretical and observational investigations. Topics examined include fly's-eye observations of ultrahigh-energy (UHE) gamma rays, recent results from the IMB detector, the theoretical implications of UHE detections of binary X-ray ...
Once quantum mechanical effects are included, the hypotheses underlying the positive mass theorem of classical general relativity fail. As an example of the peculiarities attendant upon this observation, a wormhole mouth embedded in a region of high mass density might accrete mass, giving the other mouth a net [ital negative] mass of unusual gravitational properties. The ...
It is shown that Cyg X-3 can be interpreted by means of the standard model'' for galactic x-ray sources in terms of mass loss from a large companion star and accretion on to a compact object. In the standard model'' assumed the x rays originate from a compact ...
The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field configuration for the case of ...
Accretion, the process by which matter collects into a central object, is ubiquitous and often dynamically important for astrophysical objects on the scale of compact object disks (� 1010 cm) up to that of galactic clusters (� 1024 cm). In order for matter to accrete, ...
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 ...
Accreting black holes and neutron stars in their hard (low) state show not only very similar X/?-ray spectra but also that the behavior of their light curves is quite similar which can be quantified as having similar power-density spectra and Fourier-frequency-dependent time/phase lags. Taken together this argues for a common mechanism of the X/?-ray production in these ...
have been. : size and distribution of such flux tubes. We then apply the model to identified using numerical, nonlinear hydrodynamic techniques, accretion ...
290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...
... codes for the prediction of ice accretion on aeroplanes ... NUMERICAL ANALYSIS, ICE, AVIATION SAFETY, COMPACT DISKS, ICE FORECASTING ...
DTIC Science & Technology
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? ...
Dec 19, 1999 ... Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. ...
XTE(ASM) and BATSE links to Accreting Pulsars. Last Updated: December 6, 2002 ... Undetermined Companion, Anomalous X-ray Pulsars (non-accretion objects) ...
The equations describing the transport of suprathermal charged particles, electromagnetic radiation and neutrinos across accretion flows onto compact objects are solved analytically, the effects of shocks in the flow being included. These solutions are used in discussing three illustrative astrophysical examples: acceleration of cosmic ...
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 ...
break is likely to be variable in time from blue (optical) wavelengths to several microns the transition from optically-thick to thin jet emission; based on previous broad-band photometry, this break to the environments of the primary compact objects, including an optically-thick accretion disc, a diffuse hot coronal
We derive a constraint on the pair density ratio, z(sub +) = n(sub +)/n(sub p), in an electron-positron pair wind flowing away from the central region of an accretion disk around a compact object under the assumption of a coupling between electrons, posit...
There is robust observational evidence supporting the existence of 5-20 Modot compact bodies in X-ray binary systems and of 105-109 Modot bodies at the center of many galaxies. All these objects are commonly interpreted as black holes, even is there is no direct evidence that they have an event horizon. A fundamental limit for a black hole in 4-dimensional ...
A solid theoretical understanding of how inflowing, accreting plasma around black holes and other compact objects gives rise to outflowing winds and jets is still lacking, despite decades of observations. The fact that similar processes and morphologies are observed in both X-ray binaries and active galactic nuclei has led to ...
CI Cam is a unique X-ray binary that represents either a potential new evolutionary pathway towards type Ia supernovae (if it is a white dwarf), or an ideal object to study accretion disk geometry at a regime where an advection dominated flow is expected (if it is a black hole or neutron star). However, existing data cannot discriminate between these ...
The bright and highly variable X-ray and radio source known as Cygnus X-3 was among the first X-ray sources discovered, yet it remains in many ways an enigma. It is known to consist of a massive, Wolf-Rayet primary in an extremely tight orbit with a compact object. However, one of the most basic of parameters-the mass of the compact ...
Cygnus X-3 is an accreting high-mass X-ray binary composed of a Wolf-Rayet star and an unknown compact object, possibly a black hole. The gamma-ray space telescope Fermi found definitive evidence that high-energy emission is produced in this system. We propose a scenario to explain the GeV gamma-ray emission in Cygnus X-3. In this ...
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 ...
An analysis of the effect of microlensing by a cosmologically dominant density of compact objects is
The origin of large scale magnetic fields in astrophysical rotators, and the conversion of gravitational energy into radiation near stars and compact objects via accretion have been subjects of active research for a half century. Magnetohydrodynamic turbulence makes both problems highly nonlinear, so both subjects have benefitted from ...
Accretion-powered millisecond pulsars (AMPs) are very interesting astrophysical objects. Mat-ter from accretion disk is captured by star's magnetic field and falls along the field lines, creating "hotspots" near magnetic poles of the star. Typical spectrum of an AMP contains a disk emis-sion, blackbody emission of a hotspot and a ...
Sgr A(*) is a unique, compact radio source at the Galactic center whose characteristics suggest that
The central compact objects are a newly emerging class of young neutron stars near the centre of supernova remnants. From X-ray timing and spectral measurements, their magnetic fields are determined to be �1010-1011 G, which is significantly lower than that found on most pulsars. Using the latest electrical and thermal conductivity calculations, we solve ...
We present optical spectroscopy of the microquasar SS433 covering a significant fraction of a precessional cycle of its jet axis. The components of the prominent stationary H? and H? lines are mainly identified as arising from three emitting regions: (i) a super-Eddington accretion disc wind, in the form of a broad component accounting for most of the mass loss from the ...
Symbiotic stars (SSs) and Cataclysmic Variables (CVs) are two families of binary systems which occasionally vary in brightness because of accretion from the secondary star. High frequency oscillations, also known as flickering, are thought to occur because of turbulence in the accretion disk especially in and near the vicinity of the boundary layer between ...
Variability on a variety of timescales is a commonly observed feature of astronomical systems ranging from compact binaries to active galactic nuclei. In some cases, such as those involving the x-ray emissions of certain black-hole candidates and the Z-sources among low-mass x-ray binaries, quasi-periodic oscillations are observed to exhibit periods of oscillation that are ...
During the past 8 years, extended temporal and broadband spectroscopic studies carried out by x-ray astronomical satellites have led to the identification of specific compact x-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique opportunity to study matter under extreme ...
Magnetohydrodynamic models of collimated outflows produced by accretion discs around compact objects can be used for interpreting the phenomenology of active astrophysical objects as young stellar objects, microquasars, X-ray binaries, gamma-ray bursts, extended radio galaxies and active ...
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 can solve the induction equation in terms of the magnetic vector ...
We present three numerical models of accretion from radiation driven stellar winds onto compact objects in massive X-ray binary systems. The wind is given a velocity profile consistent with a radiatively driven wind, and a 'negative mass' gravitational potential is derived from this profile to represent the wind ...
The hard X-radiation (20-200 keV) from Cyg X-3 shows a maximum at a phase 0.5 of the observed 4.8 hr modulation, while the soft X-radiation (2-12 keV) shows a maximum at a phase 0.75.Both the emissions show a minimum at a phase 0.0. This behaviour can be explained by considering the X-ray emission both by the compact object and the hot post shock gas left ...
Globular clusters (GCs) with their ages of the order of several billion years contain many final products of evolution of stars such as: neutron stars, white dwarfs and probably also black holes. These compact objects can be at present responsible for the acceleration of particles to relativistic energies. Therefore, ?-ray emission is expected from GCs as ...
The energy release due to neutralino WIMP self-annihilation in the thermalization volume inside a compact object is shown to be comparable to the energy needed to create a long-lived lump of strange quark matter, or strangelet, for WIMP masses above a few GeV. Since strange matter is the most stable state of matter, accretion of ...
Soft X-ray transients (SXTs), a sub-class of low-mass X-ray binaries (LMXBs), provide a unique opportunity to test General Relativity and to probe fundamental physics under conditions terrestrially unattainable. SXT outbursts are of great interest because they allow the study of LMXBs under a wide range of accretion rates. The majority of known SXTs contain black holes, ...
In studies of accreting black holes in binary systems, empirical relations have been proposed to quantify the coupling between accretion processes and ejection mechanisms. These processes are probed, respectively, by means of X-ray and radio/optical-infrared observations. The relations predict, given certain accretion conditions, the ...
Exosat observations are used to compare the spectral properties of the persistent emission from a number of X-ray burst sources, high-luminosity low-mass X-ray binaries (LMXRB) and galactic black hole candidates with various models for X-ray emission from an accretion disk surrounding a compact object in a binary system. It is shown ...
Steady, spherically symmetric accretion onto a compact object near the Eddington limiting luminosity is considered for an optically thick, ionized hydrogen plasma. Solutions assuming LTE are treated in detail, with non--LTE flows being briefly discussed. In contrast to previous treatments, we find that the spectrum peak for free-fall ...
Many systems of interest in general relativistic astrophysics, including neutron stars, accreting compact objects in x-ray binaries and active galactic nuclei, core collapse, and collapsars, are assumed to be approximately spherically symmetric or axisymmetric. In Newtonian or fixed-background relativistic approximations it is common ...
Shocks in advective flows around black holes have become es- sential ingredients in explaining wide variety of observed features. We first analytically study the properties of shocks in the special case when viscosity and other dissipative processes are negligible. We compare our analytical re- sults with those obtained numerically. The agreement is generally good. In the course of development of ...
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M? is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas distribution to simulate the ...
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M&sun; is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas distribution to simulate the ...
We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters the accretion rate, diffusion coefficient, ...
Observational evidence suggests a link between long duration gamma ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor ...
In recent years, much effort has been devoted to unravelling the connection between the accretion flow and the jets in accreting compact objects. In the present work, we report new constraints on these issues, through the long-term study of the radio and X-ray behaviour of the black hole candidate H1743-322. This ...
LS I +61 303 is a puzzling Be/X-ray binary with variable gamma-ray emission at up TeV energies. The nature of the compact object and the origin of the high-energy emission are unclear. One family of models invokes particle acceleration in shocks from the collision between the B-star wind and a relativistic pulsar wind, while another centers on a ...
We study the effects of a global magnetic field on viscously rotating and vertically integrated accretion discs around compact objects using a self-similar treatment. We extend Akizuki & Fukue's work by discussing a general magnetic field with three components (r, ?, z) in advection-dominated accretion flows ...
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 ...
The newly discovered broad Halpha emission line in the nuclear spectrum of M94, which is unambiguously associated with X-ray, radio, and variable UV compact source detections, identifies this object as one of the least luminous accretion-type LINERs discovered thus far, and therefore, an important example of ...
Nowadays we believe that a typical galaxy contains about 107 stellar-mass black holes and a single super-massive black hole at its center. According to general relativity, these objects are characterized solely by their mass M and by their spin parameter aast. A fundamental limit for a black hole in general relativity is the Kerr bound |aast| <= 1, but the ...
We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars, and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model that includes planet migration and disk evolution, and subsequent evolution yield consistent determinations of the ...
Our VLBA survey of nearby bright LLAGN has found high brightness temperature (.10 K) radio cores in 16 of 17 objects observed, with four of them even hosting parsec scale jets, strongly suggesting that at least 20% of LLAGN are accretion powered. Few LLAGN show the steep radio spectra expected in an advection dominated accretion flow ...
The source X-9 was discovered with the Einstein Observatory in the field of M81 and is located in the dwarf galaxy Holmberg IX. X-9 has a 0.2-4.0 keV luminosity in excess of the Eddington limit for a 1 Msolar compact accreting object, if it is at the same distance as Holmberg IX (3.4 Mpc). Past hypotheses on the nature of this ...
This paper presents procedures for designing compact spur gear sets with the objective of minimizing
Context: The combination of compact objects, short period variability and peculiar chemical composition of the ultra compact X-ray binaries make up a very interesting laboratory to study accretion processes and thermonuclear burning on the neutron star surface. Improved large optical telescopes and more sensitive ...
Spectrophotometry of the proposed optical counterpart of the hard X-ray source GX 1+4 is presented. The spectrum is that of a symbiotic star which is an M giant with a variable blue continuum and a rich emission line spectrum including H I, He I, Fe II, (Fe VII), and probably (Fe X). An explanation in terms of a compact object ...
The improved sensitivity of the XMM-Newton satellite is quickly expanding our knowledge of X-ray emission mechanisms and physical conditions in and around compact objects. Thanks to the large collecting power and high energy resolution of the EPIC and RGS instruments, detailed X-ray spectral analysis can be performed in the 0.2 to 12 keV energy range. In ...
The following topics were dealt with:- black hole thermodynamics, cosmology, Sunyaev-Zeldovich effect, Kaluza-Klein theories, Dirac equation in Kerr geometry, missing mass, compact object radiative outflows, neutron star accretion discs, astrophysical jets, nucleosynthesis around black holes, quasi-periodic oscillations, astronomical ...
Spectroscopic and photometric observations of LMC X-2 reveal the source to be an X-ray binary with a relatively long orbital period, probably 12.5 days. It appears to be a partially eclipsing system. It is one of a small subclass of low-mass X-ray binaries with longer orbital periods and higher X-ray luminosity than average, which contain a compact object ...
Accretion discs with masses ~10-3-0.1Msolar are believed to form during the merger of a neutron star (NS) with another NS and the merger of a NS with a black hole (BH). Soon after their formation, such hyperaccreting discs cool efficiently by neutrino emission and their composition is driven neutron-rich by pair captures under degenerate conditions. However, as the disc ...
We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. ...
One of the remarkable phenomena, characterizing both Galactic and extra-Galactic X-ray binary systems, is the substantial variability of a photon flux, detectable in a very broad range of timescales. For instance, the accretion flow near a black hole event horizon can produce X-ray variability on a millisecond timescale. At the same time aperiodic changes from the extended ...
Recent months have witnessed dramatic progress in our understanding of SGRBs. There is now general agreement that SGRBs can produce directed outflows of relativistic matter with a kinetic luminosity exceeding by many millions that of AGN. The requirements of energy and compactness indicate that SGRB activity can be ascribed to a modest fraction of a solar mass of gas ...
I present work on the accretion onto stellar mass black holes in several scenarios. Due to dynamical friction stellar mass black holes are expected to form high density cusps in the inner parsec of our Galaxy. These compact remnants may be accreting cold dense gas present there, and give rise to potentially observable X-ray emission. I ...
IC 10 X-1 is a bright (LX = 1038 ergs s-1) variable X-ray source in the Local Group starburst galaxy IC 10. The most plausible optical counterpart is a luminous Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet X-ray binary. In this Letter, we report on the detection of an X-ray orbital period for IC 10 X-1 of 34.4 hr. This result, combined with a reexamination of optical spectra, ...
The violent birth of black holes and neutron stars during core- collapse supernovae and merging events probes the fundamental nature of gravity, neutrinos, high-density equations of state, and beyond-QED-strength magnetic fields. Post-birth these compact objects continue to be of significant interest by powering pulsar wind nebulae, active galactic nuclei, ...
Context: Compact binary supersoft X-ray sources (CBSS) are explained as being associated with hydrostatic nuclear burning on the surface of a white dwarf with high accretion rate. This high mass transfer rate has been suggested to be caused by dynamical instability, expected when the donor star is more massive than the accreting ...
accreting star. Roughly half the known X�ray novae contain BH candidates and the rest contain NSs. X of the accreting star. As discussed in the Introduction, the accretion rate in a typical X�ray nova spans a wide in which the compact accreting primary stars are too massive to be neutron ...
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 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...
Large scale X-ray jets that extend to >100 kpc distances from the host galaxy indicate the importance of jets interactions with the environment on many different physical scales. Morphology of X-ray clusters indicate that the radio-jet activity of a cD galaxy is intermittent. This intermittency might be a result of a feedback and/or interactions between galaxies within the cluster. Here we ...
Stellar evolutionary models predict that most of the hot sub-dwarfs in close binary systems have white dwarf companions. In a few cases even more massive compact objects (neutron stars or black holes) are suggested by the optical mass functions. The X-ray emission expected from accretion of the sub-dwarf's wind can reveal the nature of ...
The radio nuclei of NGC 1275 (3C 84) and 3C 345 have been mapped at 22.2 GHz with a resolution of approx.0.4 milli-arcsec. The map of 3C 84 shows an asymmetric one-sided structure extending southward from a very compact component, identified here with the center of activity. This one-sided structure is embedded in a larger scale (30'') symmetric structure. In ...
This thesis examines aspects of subsonic reactive flows in stars. Highlighted are fluid flows in which the velocity of the fluid is much less than the local sound speed of the fluid, and where the thermodynamic conditions of the fluid are conducive to nuclear reactions. Reactive flows of this nature are capable of generating self-sustained flame fronts, also known as deflagration waves. An ...
The many similarities between the prompt emission pulses in gamma-ray bursts (GRBs) and X-ray flares during the fast decay and afterglow (AG) phases of GRBs suggest a common origin. In the cannonball (CB) model of GRBs, this common origin is mass accretion episodes of fall-back matter on a newly born compact object. The prompt emission ...
We examine the electromagnetic and gravitational wave (GW) signatures of stellar-mass compact objects (COs) spiraling into a supermassive black hole (extreme mass-ratio inspirals), embedded in a thin, radiation-pressure dominated, accretion disk. At large separations, the tidal effect of the secondary CO clears a gap. We derive the ...
Hyper-accreting discs occur in compact-object mergers and in collapsed cores of massive stars. They power the central engine of ?-ray bursts in most scenarios. We calculate the microphysical dissipation (the viscosity and resistivity) of plasma in these discs, and discuss the implications for their global structure and evolution. At the temperatures (kBT ...
We examine the possibility that hyper-accretion on to newly born black holes occurs in highly intermittent, non-asymmetric fashion favourable to gravitational-wave emission in a neutrino-cooled disc. This picture of near-hole accretion is motivated by magnetorotationally induced, ultrarelativistic disc dynamics in the region of the flow bounded from below ...
This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigen fre...
We present X-ray observations of the transient accretion-powered millisecond pulsar IGR J00291+5934 during quiescence. IGR J00291+5934 is the first source among accretion-powered millisecond pulsars to show signs of a thermal component in its quiescent spectrum. Fitting this component with a neutron star atmosphere or a blackbody model we obtain soft ...
High-luminosity active galactic nuclei (AGNs) powered by accretion onto a massive black hole (or other compact object) may have bolometric luminosities dominated by thermal emission from a geometrically thick accretion disk. Radiation from these disks is strongly anisotropic, which has important consequences for ...
We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global ...
Holmberg IX X-1 is a well-known ultraluminous X-ray source with an X-ray luminosity of ~1040 erg s-1. The source has been monitored by the X-ray telescope of Swift regularly. Since 2009 April, the source has been in an extended low luminosity state. We utilize the co-added spectra taken at different luminosity states to study the spectral behavior of the source. Simple power-law and multi-color ...
A theory of polarization of X rays emitted by magnetized neutron stars, white dwarfs and black hole accretion disks is presented and predictions are compared with polarimetric data. Polarization occurs in accreting neutron stars and white dwarfs in binary systems as plasma travels along magnetic field lines formed between the companions. Movement parallel ...
We consider the long-term evolution of debris following the tidal disruption of compact stars in the context of short gamma ray bursts. The initial encounter impulsively creates a hot, dense, neutrino-cooled disk capable of powering the prompt emission. After a long delay, we find that powerful winds are launched from the surface of the disk, driven by the recombination of ...
We propose that the intermediate luminosity optical transient NGC 300 OT2008-1 was powered by a mass transfer episode from an extreme asymptotic giant branch star to a main sequence (MS) companion. We find a remarkable similarity in the shapes of the light curves of the several months long NGC 300 OT2008-1 outburst, of the three-month long 2002 enigmatic outburst of the B star V838 Mon, and the ...
A theoretical treatment is presented of kinetic equilibria in accretion disks (AD) around compact objects, for cases where the plasma can be considered as collisionless. The plasma is assumed to be axisymmetric and to be acted on by gravitational and electromagnetic fields; in this paper, the particular case is considered where the ...
It is now generally accepted that accretion of matter onto a compact object (white dwarf, neutron star or black hole) is one of the most efficient processes in the universe for producing high energy radiations. Measurements of the {gamma}-ray emission will provide a potentially valuable means for furthering our understanding of the ...
Optical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. Although it will not resolve the emission, SIM will be very ...
Very recently the Chandra first light observation discovered a point-like source in the Cassiopeia A supernova remnant. This detection was subsequently confirmed by the analyses of the archival data from both ROSAT and Einstein observations. Here we compare the results from these observations with the scenarios involving both black holes (BHs) and neutron stars (NSs). If this point source is a BH, ...
The Rossi X-ray Timing Explorer has observed a wide range of sources and is producing valuable science. Its broad-band sensitivity has been key in the observations of both compact, stellar, and nebular objects. RXTE is ideally suited for observing X-rays from both galactic and extragalactic black holes. The range of accretion rates, ...
This chapter provides a brief overview of the timescales associated with the accretion (assemblage) of planetesimals (asteroidal-sized objects on the order of 10-100 km in diameter) in the early solar system based primarily on meteoritic studies, but also on dynamical and astronomical constraints. In the first edition of this book (Meteorites and the Early ...
Kuiper belt objects (KBOs) accreted from a m�lange of ices, carbonaceous matter, and rock of mixed interstellar and solar nebular provenance. The transneptunian region, where this accretion took place, was likely more radially compact than today. This and the influence of gas drag during the solar nebula epoch ...
Recent months have witnessed dramatic progress in our understanding of short ?-ray burst (SGRB) sources. There is now general agreement that SGRBs�or at least a substantial subset of them�are capable of producing directed outflows of relativistic matter with a kinetic luminosity exceeding by many millions that of active galactic nuclei. Given the twin requirements of energy and ...
Aims: A fraction of massive stars are expected to collapse into compact objects (accreting black holes or rapidly rotating neutron stars) that successfully produce gamma-ray bursts (GRBs). We examine the possibility of directly observing these gamma-ray burst compact objects (GCOs) using ...
Analytical arguments and a numerical hydrodynamic code are used to investigate spherically symmetric
Dec 1, 1999 ... This matter is then gravitationally captured in a rotating, pancake-shaped accretion disk around a compact partner, which is most likely a ...
... legislation in 1989 to stem the growth of landfills and improve solid waste . ... Accretion in Cradle-knoll Landscapes of Northern Wisconsin [USDA0421] ...
Phenomena occurring during the last stages of stellar evolution play a major role in galactic evolution. These are responsible for the metal enrichment of the interstellar medium; supernovae explosions can enhance star formation as a result of the propagation of the shock wave, and contribute in maintaining the hot phase of the interstellar medium at a high temperature; and it is finally possible ...
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 accretion disks. ...
In the early 1990's, isolated thermally-emitting neutron stars accreting from the interstellar medium were predicted to show up in their thousands in the ROSAT soft X-ray all-sky survey. The glut of sources would provide unprecedented opportunities for probing the equation of state of ultra-dense matter. Only seven objects have been firmly identified to ...
In the recent years, the discovery of a new class of Galactic transients with fast and bright flaring X-ray activity, the supergiant fast X-ray transients, has completely changed our view and comprehension of massive X-ray binaries. These objects display X-ray outbursts which are difficult to be explained in the framework of standard theories for the ...
It was proposed that the massive compact halo objects (MCHOs) would be produced during an earlier epoch of cosmology if the density perturbations are between 3�10-4 and 0.3. Then these objects can accrete dark matter particles onto them due to their high density. If the dark matter is in the form of the weakly ...
Sources of gravitational waves (GW) and emitters of high energy neutrinos (HE ?) both involve compact objects and matter moving at relativistic speeds. GW emission requires a departure from spherical symmetry, which is the case if clumps of matter are accreted around black holes or neutron stars, and ejected in relativistic jets, where ...
We present a linear stability analysis of a planar radiative shock with cooling function ..lambda..proportionalT/sup ..cap alpha../. We investigate an oscillatory instability similar to that found in numerical calculations of accretion onto degenerate dwarfs by Langer, Chanmugam, and Shaviv. Our analysis shows that multiple modes of oscillations are unstable for ..cap ...
We explore the effects of r-process nucleosynthesis on fallback accretion in neutron star (NS)-NS and black hole-NS mergers, and the resulting implications for short-duration gamma-ray bursts (GRBs). Though dynamically important, the energy released during the r-process is not yet taken into account in merger simulations. We use a nuclear reaction network to calculate the ...
We report the discovery of a luminous ultra-soft X-ray excess in a radio-loud narrow-line Seyfert 1 galaxy, RX J1633+4718, from archival ROSAT observations. The thermal temperature of this emission, when fitted with a blackbody, is as low as 32.5+8.0 -6.0 eV. This is in remarkable contrast to the canonical temperatures of ~0.1-0.2 keV found hitherto for the soft X-ray excess in active galactic ...
Magnetic fields are a distinctive feature of accretion disc plasmas around compact objects (i.e., black holes and neutron stars) and they play a decisive role in their dynamical evolution. A fundamental theoretical question related with this concerns investigation of the so-called gravitational MHD dynamo effect, responsible for the ...
An interesting feature found in X-ray binary observations is the change between a soft and a hard spectrum. Such transitions were observed for both neutron star and black hole systems. The soft and hard spectral state are understood as originating from accretion via a disk which reaches inward to the compact object, in the first case, ...
One of the most intriguing challenges in high-energy astrophysics has been understanding the dynamics of accretion flow onto compact objects. X-ray binaries exhibit many different patterns of accretion flow, manifested as "X- ray states". Various states show dramatically different spectral energy distributions and ...
Photoionized plasmas are encountered in astrophysics wherever low-temperature gas/plasma is bathed in a strong radiation field. X-ray line emissions in the several kiloelectronvolts spectral range were observed from accreting clouds of binary systems, such as CYGNUS X-3 and VELA X-1, in which high-intensity x-ray continua from compact ...
We investigate the deposition of energy due to the annihilations of neutrinos and antineutrinos on the rotation axis of rotating neutron and quark stars, respectively. The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around the compact object. Under the assumption of the separability of the neutrino null ...
Recent observations reveal that a majority of galaxies contain a central massive object (CMO), either a supermassive black hole (SMBH) or a compact stellar nucleus, regardless of the galaxy mass or morphological type. The masses of these CMOs correlate tightly with those of the host galaxies, MCMO~0.002Mgal. Several recent studies argue that feedback from ...
As part of a larger program to identify and characterize possible low-redshift analogs to massive compact red galaxies found at high redshift, we have examined the morphologies of three low-redshift compact galaxies drawn from the sample of Trujillo et al. Using deeper and higher resolution images, we have found faint and relatively extensive outer ...
Resistivity and bulk-density logs acquired while drilling are used to document the evolution of porosity, volumetric loss, and effective stress in the upper 300 m of the Barbados accretionary prism. The computed profiles across a thrust fault enable the separation of pre-, syn-, and post-accretion components; total volume loss is divided into normal consolidation ...
Slim disks have been received much attention because of the increasing evidence of supercritical accreting objects. In this paper, we make an attempt to construct a unified model in which the viscosity and the dimensionless accretion rate can span rather wide ranges. We replace blackbody radiation under the diffusion approximation with ...
Naked singularities are hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon. Penrose has proposed a conjecture, according to which there exists a cosmic censor who forbids the occurrence of naked singularities. Distinguishing between astrophysical black holes and naked singularities is a major challenge for present day ...
Radiation spectra modelling of accretion flows in close binary systems is considered. The modern state of such modelling is reviewed. The review is mainly based on the works, performed by the author with collaborators, where the basic parameters of compact stars are obtained from radiation spectra. For a start, the physical processes of energy generation ...
The aim of this thesis was to investigate the influence of gravitational microlensing on detected X-ray radiation from accretion disks of active galactic nuclei (AGN). More precisely, the variations of the Fe K ? spectral line and X-ray continuum caused by gravitational microlensing were analyzed, as well as the corresponding time scales and microlensing optical depth (i.e. ...
... The objective of this research is to exploit advances in nanoscience to enable new capabilities in compact biofuel cells. ...
A star acquires much of its mass by accreting material from a disk. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative feedback, during which a protostar is ...
We herein present an observational and theoretical review of the winds of compact binaries. After a brief consideration of the accretion disk coronae and winds of X-ray binaries, the review concentrates on the winds of cataclysmic variables (CVs). Specifically, we consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ...
opportunity to study rapid variations in stars that are very compact, like white dwarfs and neutron stars exotic neutron stars. How does accretion occur in binary stars? Two stars in orbit around each other up like compact stars (black holes, neutron stars or white dwarfs) and are accreting matter from
We present a compilation of spectroscopic observations of the sgB[e] star CI Cam, the optical counterpart of XTE J0421+560. This includes data from before, during, and after its 1998 outburst, with quantitative results spanning 37 years. The object shows a rich emission line spectrum originating from circumstellar material, rendering it difficult to determine the nature of ...
