A critical condition is obtained for which carbon deflagration induces collapse of an accreting C + O white dwarf, not explosion. If the carbon deflagration is initiated at central density as high as 10/sup 10/ g cm/sup -3/ and if the propagation of the deflagration wave is slower than approx. 0.15 upsilon/sub s/ (upsilon/sub s/ is the ...

Gravitational wave emission from stellar collapse has been studied for nearly four decades. Current state-of-the-art numerical investigations of collapse include those that use progenitors with more realistic angular momentum profiles, properly treat microphysics issues, account for general relativity, and examine non-axisymmetric effects in three ...

Gravitational-wave emission from stellar collapse has been studied for nearly four decades. Current state-of-the-art numerical investigations of collapse include those that use progenitors with more realistic angular momentum profiles, properly treat microphysics issues, account for general relativity, and examine non-axisymmetric effects in three ...

The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass accretion rate. Relatively fast accretion leads to a carbon ...

Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,

The accretion-induced collapse (AIC) of a white dwarf (WD) may lead to the formation of a protoneutron star and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in Type Ia supernovae. Motivated by the need for systematic ...

Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as to whether or not ...

The stellar origin of gamma-ray bursts can be explained by the rapid release of energy in a highly collimated, extremely relativistic jet. This in turn appears to require a rapidly spinning highly magnetised stellar core that collapses into a magnetic neutron star or a black hole within a relatively massive envelope. We hypothesize a binary star model that ends with the ...

We study accretion-induced collapse of magnetized white dwarfs as an origin of millisecond pulsars. We apply magnetized accretion disk models to the precollapse accreting magnetic white dwarfs and calculate the white dwarf spin evolution. If the pulsar magnetic field results solely from the flux-frozen fossil white ...

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

Recent three-dimensional simulations of core-collapse supernovae have revealed the existence of non-axisymmetric modes of the Spherical Accretion Shock Instability, or SASI. Here we investigate the growth of these modes using two-dimensional simulations of the accretion flow in the equatorial plane of a ...

By combining the numerical solution of the nonlinear hydrodynamics equations with the solution of the linear inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations, we investigate the properties of the gravitational radiation emitted during the axisymmetric accretion of matter onto a Schwarzschild black hole. The matter models considered include quadrupolar dust shells and ...

I perform and analyze the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure ...

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low ...

The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass ac...

A white dwarf (WD) approaching the Chandrasekhar mass may in several cases undergo accretion-induced collapse (AIC) to a neutron star (NS) before a thermonuclear explosion ensues. It has generally been assumed that AIC does not produce a detectable supernova (SN). If, however, the progenitor WD is rapidly rotating (as may be expected due to its prior ...

We present 2.5-dimensional radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from two-dimensional rotational equilibrium configurations, thereby accounting consistently for the effects of rotation prior to and after core collapse. We focus our study on a 1.46 and a 1.92 Msolar a ...

The collapse of dense cores with metallicities 0-1 Z sun is studied by hydrodynamical calculations coupled with detailed chemical and radiative processes. For this purpose, we construct a simple chemical network with non-equilibrium reactions among 15 chemical species, H+, e, H, H2, D+, D, HD, C+, C, CO, CO2, O, OH, H2O, and O2, which reproduces the abundance of important ...

The collapse of dense cores with metallicities 0-1 Z{sub sun} is studied by hydrodynamical calculations coupled with detailed chemical and radiative processes. For this purpose, we construct a simple chemical network with non-equilibrium reactions among 15 chemical species, H{sup +}, e, H, H{sub 2}, D{sup +}, D, HD, C{sup +}, C, CO, CO{sub 2}, O, OH, H{sub 2}O, and O{sub 2}, ...

... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...

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 ...

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To ...

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To ...

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To ...

We have performed 2.5D radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations of a 1.92-Msolar model. Electron capture leads to the collapse to nuclear densities of the core within a few tens of milliseconds. The shock generated at bounce moves ...

We here investigate the possibility that the ultra-high-energy cosmic-ray (UHECR) events observed above the Greisen-Zatsepin-Kuzmin (GZK) limit are mostly protons accelerated in reconnection sites just above the magnetosphere of newborn millisecond pulsars that are originated by accretion-induced collapse (AIC). We formulate the requirements for the ...

The accretion-induced collapse (AIC) of a white dwarf may lead to the formation of a protoneutron star and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in type Ia supernovae. In the AIC scenario, the supernova explosion ...

The accretion-induced collapse (AIC) of a white dwarf may lead to the formation of a protoneutron star and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in type Ia supernovae. In the AIC scenario, the supernova explosion ...

The origin of ultra-compact binaries composed of a neutron star and a low-mass (about 0.06 solar mass) white dwarf is considered. Taking account of the systemic losses of mass and angular momentum, it was found that a serious difficulty exists in the scenarios which involve tidal captures of a normal star (a main sequence star or a red giant) by a neutron star. This difficulty can be avoided if a ...

Astronomers have proposed a number of mechanisms to produce supernova explosions. Although many of these mechanisms are now not considered primary engines behind supernovae (SNe), they do produce transients that will be observed by upcoming ground-based surveys and NASA satellites. Here, we present the first radiation-hydrodynamics calculations of the spectra and light curves from three of these ...

Astronomers have proposed a number of mechanisms to produce supernova explosions. Although many of these mechanisms are now not considered primary engines behind supernovae (SNe), they do produce transients that will be observed by upcoming ground-based surveys and NASA satellites. Here, we present the first radiation-hydrodynamics calculations of the spectra and light curves from three of these ...

We have explored the dynamics of the stalled accretion shock in core collapse supernovae using large-scale three-dimensional hydrodynamics simulations on the Cray X1 at the National Center for Computational Sciences (Oak Ridge National Laboratory). We confirmed the dominance of the l=1 mode of the SASI in the linear regime, as first seen in two-dimensional ...

We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the ...

We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the ...

In this paper, the second of a series, we study the stellar dynamical and evolutionary processes leading to the formation of compact binaries containing neutron stars (NSs) in dense globular clusters. For this study, 70 dense clusters were simulated independently, with a total stellar mass ~2 � 107Msolar, exceeding the total mass of all dense globular clusters in our Galaxy. We find that, in ...

Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the accretion-induced collapse (AIC) of ...

The usual description of self-induced neutrino flavor conversions in core-collapse supernovae is based on the dominance of the neutrino density n? over the net electron density ne. However, this condition is not met during the post-bounce accretion phase, when the dense matter in a SN is piled up above the neutrinosphere. As recently ...

We explore explosions of massive stars, which are triggered via the quark-hadron phase transition during the early post-bounce phase of core-collapse supernovae. We construct a quark equation of state, based on the bag model for strange quark matter. The transition between the hadronic and the quark phases is constructed applying Gibbs conditions. The resulting quark-hadron ...

Work presented here addresses the issue of grain accretion, an essential yet poorly understood process in planetary system formation, linking the dynamically modeled steps of temperature-dependent condensation of gases after proto-sun gravitational collapse to coalescence of kilometer-size planetesimals into planets. The mechanism for grain ...

We investigate numerically and semi-analytically the collapse of low-mass, rotating prestellar cores. Initially, the cores are in approximate equilibrium with low rotation (the initial ratio of thermal to gravitational energy is ?0~= 0.5, and the initial ratio of rotational to gravitational energy is ?0= 0.02-0.05). They are then subjected to a steady increase in external ...

We study the formation of the first generation of stars in the standard cold dark matter model. We use a very high resolution cosmological hydrodynamic simulation that achieves a dynamic range of ~1010 in length scale. With accurate treatment of atomic and molecular physics, including the effect of molecular line opacities and cooling by collision-induced continuum emission, ...

Massive stars influence the surrounding universe far out of proportion to their numbers through ionizing radiation, supernova explosions, and heavy element production. Their formation requires the collapse of massive interstellar gas clouds with very high accretion rates. We discuss results from the first three-dimensional simulations of the gravitational ...

The study of short-duration gamma-ray bursts (GRBs) experienced a complete revolution in recent years thanks to the discovery of the first afterglows and host galaxies starting in May 2005. These observations demonstrated that short GRBs are cosmological in origin, reside in both star forming and elliptical galaxies, are not associated with supernovae, and span a wide isotropic-equivalent energy ...

cAMP-Mediated Regulation of Neurotrophin-Induced Collapse of Nerve Growth Cones Qun Wang and James that acutely applied brain-derived neurotrophic factor (BDNF) induces rapid growth cone collapse and neurite the collapsing action. BDNF-induced growth cone ...

When hot steam replaces cold condensate in a horizontal or almost horizontal pipe, a steam bubble collapse induced water hammer often results. The effect of condensate drainage velocity and pipe declination on the incidence of steam bubble collapse induce...

The Chandrasekhar limit is of key importance for the evolution of white dwarfs in binary systems and for the formation of neutron stars and black holes in binaries. Mass transfer can drive a white dwarf in a binary over the Chandrasekhar limit, which may lead to a Type Ia supernova (in case of a CO white dwarf) or an Accretion-Induced Collapse (AIC, in ...

Using the population synthesis binary evolution code StarTrack, we present theoretical rates and delay times of Type Ia supernovae arising from various formation channels. These channels include binaries in which the exploding white dwarf reaches the Chandrasekhar mass limit (DDS, SDS, and helium-rich donor scenario) as well as the sub-Chandrasekhar mass scenario, in which a white dwarf ...

The accretion-induced collapse (AIC) of a white dwarf to form a neutron star can leave behind a rotationally supported disc with mass of up to ~ 0.1 Msolar. The disc is initially composed of free nucleons but as it accretes and spreads to larger radii, the free nucleons recombine to form helium, releasing sufficient energy to unbind ...

The accretion-induced collapse (AIC) of a white dwarf to form a neutron star can leave behind a rotationally supported disk with mass of up to ~ 0.1 M_sun. The disk is initially composed of free nucleons but as it accretes and spreads to larger radii, the free nucleons recombine to form helium, releasing sufficient energy to unbind the ...

We present simulations of collapsing 100 M&sun; mass cores in the context of massive star formation. The effect of variable initial rotational and magnetic energies on the formation of massive stars is studied in detail. We focus on accretion rates and on the question under which conditions massive Keplerian discs can form in the very early ...

The magnetic fields affect collapse of molecular cloud cores. Here, we consider a collapsing core with an axial magnetic field and investigate its effect on infall of matter and formation of accretion disk. For this purpose, the equations of motion of ions and neutral infalling particles are numerically solved to obtain the streamlines ...

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 > ...

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. ...

Previous high-resolution cosmological simulations predicted that the first stars to appear in the early universe were very massive and formed in isolation. Here, we discuss a cosmological simulation in which the central 50 M(o) (where M(o) is the mass of the Sun) clump breaks up into two cores having a mass ratio of two to one, with one fragment collapsing to densities of ...

Previous high resolution cosmological simulations predict the first stars to appear in the early universe to be very massive and to form in isolation. Here we discuss a cosmological simulation in which the central 50M{sub {circle_dot}} clump breaks up into two cores, having a mass ratio of two to one, with one fragment collapsing to densities of 10{sup -8}g cm{sup -3}. The ...

We studied the standing accretion shock instability (SASI) for a core-collapse supernova explosion. SASI induces a nonspherically symmetric motion of a standing spherical shock wave. In order to investigate the growth of SASI, we solved the three-dimensional compressible Euler equations using ZEUS-MP/2 code based on the ...

We study nucleosynthesis of p-nuclei in the carbon deflagration model for Type Ia supernovae (SNe Ia) by assuming that seed nuclei are produced by the s-process in accreting layers on a carbon-oxygen white dwarf during mass accretion from a binary companion. We find that about 50 % of the p-nuclides are synthesized in proportion to the solar abundance and ...

In this contribution we discuss how neutron stars are produced and retained in globular clusters, outlining the most important dynamical channels and evolutionary events that affect the population of mass-transferring binaries with neutron stars and result in the formation of recycled pulsars. We confirm the importance of electron-capture supernovae in globular clusters as the major supplier of ...

There are two dominant models of how stars form. Under gravitational collapse, star-forming molecular clumps, of typically hundreds to thousands of solar masses (M(o)), fragment into gaseous cores that subsequently collapse to make individual stars or small multiple systems. In contrast, competitive accretion theory suggests that at ...

One possible scenario for the formation of massive black holes (BHs) in the early Universe is from the direct collapse of primordial gas in atomic-cooling dark matter haloes in which the gas is unable to cool efficiently via molecular transitions. We study the formation of such BHs, as well as the accretion of gas on to these objects and the high energy ...

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 rays, generation of spectral continua in ...

An analytical model for the accretion of matter onto a collapsed, massive object is employed to calculate the resulting gamma ray emissions and their origins. The accreting gas is assumed to be a fully ionized plasma featuring Maxwellian electron and proton momentum distributions, an isotropic angular distribution of electrons and ...

We study properties of gravitational waves based on the three-dimensional (3D) simulations, which demonstrate the neutrino-driven explosions aided by the standing accretion shock instability (SASI). Pushed by evidence supporting slow rotation prior to core-collapse, we focus on the asphericities in neutrino emissions and matter motions outside the ...

We examine theoretically the behaviour of the inner accretion disk in GRS 1915+105 when soft X-ray dips are present in the X-ray light curve. We assume the presence of a radial shock in the accretion disk, as in some of the Two Component Advective Flow (TCAF) solutions. We discuss the behaviour of the flux tubes inside a TCAF (which we name Magnetized TCAF ...

A cloud of gas collapsing under gravity will fragment. We present a new theory for this process, in which layers of shocked gas fragment due to their gravitational instability. Our model explains why angular momentum does not inhibit the collapse process. The theory predicts that the fragmentation process produces objects which are significantly smaller ...

We study the statistics of 61 measured masses of neutron stars (NSs) in binary pulsar systems, including 18 double NS (DNS) systems, 26 radio pulsars (10 in our Galaxy) with white dwarf (WD) companions, 3 NSs with main-sequence companions, 13 NSs in X-ray binaries, and one undetermined system. We derive a mean value of M = 1.46 � 0.30 M?. When the 46 NSs with measured spin periods are divided ...

Aims: We investigate the influence of turbulent viscosity on the collapse of a rotating molecular cloud core with axial symmetry, in particular, on the first and second collapse phase, as well as the evolution of the second (protostellar) core during its first accretion period. By using extensive numerical calculations, we monitor the ...

Mining explosions and collapses, in addition to earthquakes, may trigger the future Comprehensive Test Ban Treaty (CTBT) monitoring system. Most naturally occurring mine collapses have source mechanisms similar to a closing void which might provide a physical basis to discriminate them from explosions. In this study, an explosively ...

If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae an...

Theoretical models of cosmic gamma bursts fall into four categories: extra galactic models, flares, accretion onto collapsed stars, and exotic mechanisms. Factors such as source properties, source dimensions, and radiation mechanisms are considered, in discussing these models. 36 references. (BJG)

A dusty plasma cloud in space has a gravitational instability which allows star formation even orders of magnitude below the Jeans limit for gravitational collapse. This instability leads to a stellesimal accretion which is analogous to the planetesimal a...

We present the first numerical result of fully general relativistic axisymmetric simulations for the collapse of a rotating high-entropy stellar core to a black hole and an accretion disk. The simulations are performed taking into account the relevant microphysics. We adopt as initial conditions a spherical core with constant electron fraction (Ye = 0.5) ...

This paper discusses the following topics on the origin of the solar systems: derivation of candidate angular momentum transfer equations; dust ring identified; classic accretional problems in planetary formation; formation of the outer planets; outer sol...

We use 2D numerical simulations to study the linear response of the stalled accretion shock during the first few hundred milliseconds after core bounce in core-collapse supernovae. We use these simulations to measure the growth rate and frequency of the Spherical Accretion Shock Instability, or SASI. These simulations demonstrate that ...

During recent drop tests of a prototype weapon system, the parachute collapsed soon after it became fully inflated. The magnitude and duration of the collapses were severe enough to degrade parachute performance drastically. A computer-assisted analysis i...

We present a review of the possible sources for r-process nuclei. It is known that there is as yet no self-consistent mechanism to provide abundant neutrons for a robust r-process in the neutrino-driven winds from nascent neutron stars. We consider that the heavy r-nuclei with mass numbers A>130 (Ba and above) cannot be produced in the neutrino-driven winds. Nonetheless, the r-process and the ...

Accretion from a disk onto a collapsed, relativistic star--a neutron star or black hole--is the mechanism widely believed to be responsible for the emission from compact X-ray binaries. Because of the extreme spatial resolution required, is not yet possib...

.1 Planetological History of the Early Earth Chapter 2 described how the collapse of the core of an interstellar3 The Earth The previous chapter brie y outlined how from an accretion disk ? the end product to look more closely at the basic structure and composition of the singular planet Earth where life

The results of self-consistent, azimuthally symmetric, radiation-hydrodynamic calculations of subcritical accretion disks about a Newtonian pseudo-black hole are reported. Energy generation is described by a kinematic viscosity law and a modified alpha-disk model. A disk with constant kinematic viscosity settles to a nearly steady state which approximates a thin disk solution. ...

Riverbank erosion is known to be strongly fluvially controlled and determination of shear stresses at the bank surface and at the bank toe is a crucial point in bank erosion modeling. In many modeling attempts hydraulics are simulated separately in a hydrodynamic-numerical model and the simulated shear stresses are further applied onto the bank surface in a bank erosion model. Hydrodynamics are ...

Evidence is growing for a class of gamma-ray bursts (GRBs) characterized by an initial ~0.1-1 s spike of hard radiation followed, after a ~3-10 s lull in emission, by a softer period of extended emission lasting ~10-100 s. In a few well-studied cases, these `short GRBs with extended emission' show no evidence for a bright associated supernova (SN). We propose that these events are produced by the ...

We present the results of numerical experiments in which we study how asphericities induced by the growth of the standing accretion shock instability (SASI) produce gravitational waveforms in the postbounce phase of core-collapse supernovae. To obtain the neutrino-driven explosions, we parameterize the neutrino fluxes emitted from the ...

This paper discusses the following topics on the origin of the solar systems: derivation of candidate angular momentum transfer equations; dust ring identified; classic accretional problems in planetary formation; formation of the outer planets; outer solar system satellites; rock rings; comets; the asteroids; formation of the inner planets; meteoric formation processes; ...

Solid recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that

Solid recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that

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 accreting ...

We interpret the recently observed super-long cosmic gamma-ray burst GRB 110328A in the model of collapsing galactic nucleus. The neutron stars and stellar-mass black holes can form evolutionary a compact self-gravitating subsystem in galactic center. Merges of these star remnants during the avalanche contraction and collapse of the cluster can explain the ...

Even under idealized conditions of spherical infall, the shock wave generated in the canonical core-collapse model for Type II supernovae does not remain spherical. We examine the inherent asymmetry of the stalled shock wave in core-collapse supernovae using an idealized model of a standing accretion shock. We show that although this ...

A hypermassive neutron star (HMNS) is a possible transient formed after the merger of a neutron-star binary. In the latest axisymmetric magnetohydrodynamic simulations in full general relativity, we find that a magnetized HMNS undergoes "delayed" collapse to a rotating black hole (BH) as a result of angular momentum transport via magnetic braking and the magnetorotational ...

We present new results on the gravitational wave (GW) emission in the postbounce phase of nonrotating or slowly rotating core-collapse supernovae obtained from an extensive set of simulations with the 2D code BETHE/Hydro. Our calculations include the most recent presupernova stellar models, a finite-temperature nuclear equation of state and a prescription for neutrino cooling ...

Star formation is such a complex process that accurate numerical tools are needed to quantitatively examine the mass distribution and accretion of fragments in collapsing, turbulent, magnetized gas clouds. To enable a numerical treatment of this regime, we implemented sink particles in the adaptive mesh refinement (AMR) hydrodynamics code FLASH. Sink ...

We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough ...

We present a unified model for molecular core formation and evolution, based on numerical simulations of converging, supersonic flows. Our model applies to star formation in giant molecular clouds dominated by large-scale turbulence, and contains four main stages: core building, core collapse, envelope infall, and late accretion. During the building stage, ...

We argue that jittering jets, i.e. jets that have their launching direction rapidly change, launched by the newly formed neutron star in a core-collapse supernova can explode the star. We show that under a wide range of parameters the fast narrow jets deposit their energy inside the star via shock waves, and form two hot bubbles, that eventually merge, accelerate the rest of ...

We argue that jittering jets, i.e. jets that have their launching direction rapidly change, launched by the newly formed neutron star in a core-collapse supernova can explode the star. We show that under a wide range of parameters the fast narrow jets deposit their energy inside the star via shock waves, and form two hot bubbles, that eventually merge, accelerate the rest of ...

Primordial stars are formed from a chemically pristine gas consisting of hydrogen and helium. They are believed to have been born at some early epoch in the history of the Universe and to have enriched the interstellar medium with synthesized heavy elements before the emergence of ordinary stellar populations. We study the formation of the first generation of stars in the standard cold dark matter ...

The massive stellar progenitor of a hypernova explosion and an associated gamma-ray burst must satisfy two primary constraints: (1)the outer layers of the stellar core must possess sufficient angular momentum to form a centrifugally supported torus about the collapsed central object (a Kerr black hole); and, (2)the envelope of the star must not be excessively massive or ...

We develop an exploratory model for the outer, gravitationally unstable regions of accretion disks around massive black holes. We consider black holes of mass 10(6) to 10(10) Msun, and primeval or solar abundances. In a first step we study star formation and evolution in a purely gaseous marginally unstable disk, and we show that unstable fragments should ...

The growth of galaxies is driven by two processes: mergers with other galaxies and smooth accretion of intergalactic gas. The relative share of this two processes depends on the environment (rich cluster or field), and determines the morphological evolution of the galaxy. In this work we focus on the properties of accretion onto galaxies. Through numerical ...

... In summary, we have observed current collapse induced in MOCVD- and MBE-grown GaN HEMT structures by short-term bias stress. ...

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 neutrino transport on the disk structure. We ...

Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find ...

Neutrinos from core collapse supernovae can be emitted from a rapidly accreting disk surrounding a black hole, instead of the canonical protoneutron star. For galactic events, detector count rates are considerable and in fact can be in the thousands for Super-Kamiokande. The rate of occurrence of these accreting disks in the Galaxy is ...

In this paper, we bring together various of our published and unpublished findings from our recent 2D multi-group, flux-limited radiation hydrodynamic simulations of the collapse and explosion of the cores of massive stars. Aided by 2D and 3D graphical renditions, we motivate the acoustic mechanism of core-collapse supernova explosions and explain, as best ...

Nonequilibrium molecular dynamics (MD) simulations show that shock-induced void collapse in copper occurs by emission of shear loops. These loops carry away the vacancies which comprise the void. The growth of the loops continues even after they collide and form sessile junctions, creating a hardened region around the collapsing void. ...

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 compactness, it ...

The modern Anatolian-African plate boundary is represented by a north-dipping subduction zone that is part of a broad domain of regional convergence between Eurasia and Afro-Arabia since the latest Mesozoic. High- pressure metamorphic rocks occur along suture zones and in core complexes in the upper plate (Eurasia) of this convergence zone. A series of collisions between Gondwana-derived ribbon ...

Particle simulations are performed to show that the ion waves resulting from Stimulated Brillouin Scatter (SBS) can trigger the collapse of the plasma waves excited by Stimulated Raman Scatter (SRS). We discuss the effect of this collapse mechanism on the hot-electron spectrum produced by the electrostatic waves. A fluid model for the coupling of the ion ...

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 larger than M, the accretion onto the ...

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. ...

A core collapse supernova marks the death of a star over 8 times the size of the sun. Sometimes in the aftermath of these explosions a spinning, magnetized, neutron star can be left behind, also known as a pulsar. It has recently been discovered that pulsar spins can arise through a spiral spherical accretion shock instability (SASI) of a supernova. This ...

We present the discovery, photometric, and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with ? d = 5 days and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M r = -17 mag and has mean velocities of 10,000 km s-1. Our light curve modeling suggests a radioactivity-powered event and an ejecta mass of 0.16 M sun. If ...

The Kepler observatory was designed to discover transits by Earth-like planets orbiting Sun-like stars. Its first major discoveries, however, are hot objects in close orbits around main-sequence stars. These are likely to be white-dwarf remnants of stars that have transferred mass to the present-day main sequence stars. These particular main-sequence stars are among the Kepler targets because they ...

The evolutionary scenario of neutron star binaries is still an essential enigma in both stellar astrophysics and high energy astrophysics. In order to explore the scenario, we include the accumulation of data on the orbits and spins of compact binaries in multi-wavelength ranging from radio to X-ray, such as radio pulsar binaries, HMXBs, and LMXBs, filling them into the so called �Corbet ...

We present radiation hydrodynamics simulations of the collapse of massive pre-stellar cores. We treat frequency dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, it is possible for the first time to simulate the whole ...

Hypermassive neutron stars (HMNSs)--equilibrium configurations supported against collapse by rapid differential rotation--are possible transient remnants of binary neutron-star mergers. Using newly developed codes for magnetohydrodynamic simulations in dynamical spacetimes, we are able to track the evolution of a magnetized HMNS in full general relativity for the first time. ...

The late bolometric light curves of type Ia supernovae, when measured accurately over several years, show an exponential decay with a 56d half-life over a drop in luminosity of 8 magnitudes (10 half-lives). The late-time light curve is thought to be governed by the decay of Co{sup 56}, whose 77d half-life must then be modified to account for the observed decay time. Two mechanisms, both relying ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's accretion shock. Accordingly, we have ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's accretion shock. Accordingly, we have ...

The self-sustained turbulence that develops in magnetized accretion disks is suppressed in the weakly ionized, quiescent disks of close binary stars. Because accretion still proceeds during quiescence, another viscosity mechanism operates in these systems. An anticorrelation of the recurrence times of SU UMa dwarf novae with their mass ratio supports ...

Accretional temperature profiles for Saturn�s large moon Titan are used to determine the conditions needed for accretion to avoid global melting as a function of the timing, duration, and nebular conditions of Titan�s accretion. We find that Titan can accrete undifferentiated in a �gas-starved� disk even ...

Many accreting neutron stars do so intermittently; that is, the accretion ceases for long quiescent intervals. During the accretion outburst, reactions are induced in the crust by the continual accumulation of matter. These reactions heat the crust out of thermal equilibrium with the core, and when ...

Many accreting neutron stars do so intermittently; that is, the accretion ceases for long quiescent intervals. During the accretion outburst, reactions are induced in the crust by the continual accumulation of matter. These reactions heat the crust out of thermal equilibrium with the core, and when ...

Mergers of supermassive black hole binaries release peak power of up to approximately 10(57) erg s(-1) in gravitational waves (GWs). As the GWs propagate through ambient gas, they induce shear and a small fraction of their power is dissipated through viscosity. The dissipated heat appears as electromagnetic (EM) radiation, providing a prompt EM counterpart to the GW signal. ...

We simulate the formation and chemodynamical evolution of 124 elliptical galaxies using a GRAPE-SPH code that includes various physical processes that are associated with the formation of stellar systems: radiative cooling, star formation, feedback from Type II and Ia supernovae and stellar winds, and chemical enrichment. In our cold dark matter (CDM)-based scenario, galaxies form through the ...

Capillary-force-induced collapse of high-aspect-ratio (HAR) micro- and nano-structures is common in the evaporation-drying process and a number of applications based on the collapse have been proposed. However, the collapse of small HAR structures is usually uncontrollable, which has prevented it from being used in ...

Rotation-powered radio pulsars are born with inferred initial rotation periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae. In the traditional picture, this fast rotation is the result of conservation of angular momentum during the collapse of a rotating stellar core. This leads to the inevitable conclusion that pulsar spin is ...

The final composition of giant planets formed as a result of gravitational instability in the disk gas depends on their ability to capture solid material (planetesimals) during their �pre-collapse� stage, when they are extended and cold, and contracting quasi-statically. The duration of the pre-collapse stage is inversely proportional roughly to the ...

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 accretion flow. Here, we analyze the self-gravity of the forming ...

PLC and Fe line variability induced by light bending when an intrinsically constant source changes height. The Fe line varies with much smaller amplitude ...

... Nutrition during pregnancy. ... J, Lindmark G, Gebre-Medhin M. Maternal fat stores and fat accretion during pregnancy in relation to infant birthweight. ...

Building upon the strengths of its ice accretion modeling and ground testing capability, NASA has developed a broad portfolio of icing related research ...

Bubble collapse following a thermal shock in liquid mercury is investigated to understand the resulting cavitation erosion. A conservative high-order accurate interface- and shock-capturing scheme is used to carry out direct simulations of the three-dimensional collapse of a single bubble. Both the shock-induced ...

We describe a model within the "quark-nova" scenario to interpret the recent observations of early X-ray afterglows of long gamma-ray bursts (GRBs) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. STAGE 1 is an accreting (proto-) neutron star leading to a possible delay between the core ...

Most early radiative transfer calculations of protostellar collapse have suggested an upper limit of approx40 M{sub sun} for the final stellar mass before radiation pressure can exceed the star's gravitational pull and halt the accretion. Here we perform further collapse calculations, using frequency-dependent radiation ...

Carbon-oxygen white dwarfs formed in close binary systems may become unstable by mass accretion. Recent results concerning carbon-oxygen separation at the freezing point during the phase of cooling may have very important consequences for the problem of neutron star formation. The central, high-density regions of the star are then made of pure oxygen, the carbon being rejected ...

Numerous highway embankments experience post-construction settlement problems, such as bridge approach settlement that results in the 'bump at the end of the bridge'. One of the causes may be wetting-induced collapse settlement or simply, collapse settlem...

PSR J1744-3922 is a binary pulsar exhibiting highly variable pulsed radio emission. We report on a statistical multifrequency study of the pulsed radio flux variability which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase. The pulsar has an unusual combination of characteristics compared to typical ...

We propose a ray-tracing method to estimate gravitational waves (GWs) generated by anisotropic neutrino emission in supernova cores. To calculate the gravitational waveforms, we derive analytic formulae in a useful form, which are applicable also for three-dimensional computations. Pushed by evidence of slow rotation prior to core-collapse, we focus on asphericities in ...

The authors have analyzed magnetic effects which may occur in rapidly rotating core collapse supernovae. They consider effects from both magnetic turbulence and the formation of magnetic bubbles. For magnetic turbulence they have made a perturbative analysis for the spherically symmetric core-collapse supernova model that incorporates the build up of ...

All the current r-process scenarios relevant to core-collapse supernovae are facing severe difficulties. In particular, recent core-collapse simulations with neutrino transport show no sign of neutron-rich wind from a proto-neutron star. In this paper, we discuss nucleosynthesis of the r-process in an alternative astrophysical site, ``black hole wind'', ...

Aims: The radiation from newly born stars photoevaporates their parental neutral cloud, leading to the formation of dense clumps that will eventually form stars. Methods: We present 3D simulations of the interaction of a neutral cloud with an external ionising radiation field, and compute the angular momenta of these collapsing clumps. Results: The angular momenta of these ...

Radiative feedback and magnetic field are understood to have a strong impact on the protostellar collapse. We present high resolution numerical calculations of the collapse of a 1 Msolar dense core in solid body rotation, including both radiative transfer and magnetic field. Using typical parameters for low-mass cores, we study thoroughly the effect of ...

We discuss possible implications of strong primordial magnetic fields, which may have been created during cosmic inflation or the QCD / electroweak phase transition, and explore how they influence the epoch of reionization and primordial star formation. Globally, magnetic fields may delay reionization, as the magnetic pressure suppresses gravitational collapse in small halos. ...

We present high spectral resolution millimeter mapped observations of seven prestellar cores in the Coalsack, including imaging in five optically thin molecular species of the kinematic structure of two of the densest cores, C2 and C4. Various collapse-critical indices are calculated; critical masses needed for collapse are consistently greater than those ...

A new, general relativistic, hydrodynamical computer code for spherical, stellar colapse to neutron stars and black holes is presented. The code is employed to construct spacetimes for the geometrodynamical evolution of spherical masses which are initially at rest and obey an adiabatic GAMMA-law equation of state. Collapse to a black hole can be followed accurately; the ...

The evolution and stability of pair-supercritical accretion disks are examined. The microphysics of electron-positron pair processes are incorporated into a self-consistent accretion disk model, using the full set of time-dependent equations for a two-temperature disk cooled by bremsstrahlung protons with Comptonization included. It is found that the high ...

A series of simplified evolutionary calculations are used to show that deuterium burning acts as an effective thermostat in low-mass protostars over a plausible range of initial conditions and mass accretion rates. The thermostat keeps the central temperature of the accreting hydrostatic core close to 10 to the 6th K, and thereby tightly constrains the ...

These proceedings include papers presented at the Accretion Processes in Astrophysical Systems: Some Like It Hot Conference held in October, 1997 in Maryland, USA. The conference concentrated on the apparent generality of the disk{minus}wind{minus}jet geometry on scales ranging from protostars to the centers of active galactic nuclei. Some of the topics discussed include, ...

The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the ...

The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the ...

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 ...

Massive stars produce so much light that the spherically averaged radiation pressure exerted on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional adiation-hydrodynamic simulations of the collapse of a massive ...

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 compact object formation/inspiral ...

We propose a Galactic model for the isotropic component of gamma-my bursts (GB`s) based upon high-velocity neutron stars (NS`s) that have accretion disks. The fast NS`s are formed in tidally locked binaries, leading to a unique fast NS population. The tidal locking occurs due to the meridional circulation caused by the conservation of angular momentum of the tidal lobes. These ...

Neutron stars in general have space velocities much higher than their progenitors. This is believed to be the result of momentum kicks imparted during core collapse. However, the nature of the kick remains an open question. Abetted by recent progress in measuring pulsar proper motions and spin orientations, it has become possible to make improved comparison between the ...

Long ?-ray bursts may be produced by hypernova events in the rapidly rotating cores of massive stars. A serious problem that must be confronted in this scenario is how the core of the hypernova progenitor retains or acquires sufficient angular momentum to produce the requisite axisymmetric collapse. Physical processes during the evolution of an isolated massive star will tend ...

If long ?-ray bursts are produced by hypernovae, a problem that must be confronted is how the core of the hypernova progenitor retains or acquires sufficient angular momentum to produce the requisite axisymmetric collapse. Physical processes during the evolution of an isolated massive star will tend to extract any initial angular momentum from the stellar core, rendering it ...

We present radiation hydrodynamic simulations of the collapse of massive pre-stellar cores. We treat frequency-dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, for the first time it is possible to simulate the whole ...

We present radiation hydrodynamic simulations of the collapse of massive pre-stellar cores. We treat frequency-dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, for the first time it is possible to simulate the whole ...

A long-standing problem in low-mass star formation is the "luminosity problem," whereby protostars are underluminous compared to the accretion luminosity expected both from theoretical collapse calculations and arguments based on the minimum accretion rate necessary to form a star within the embedded phase duration. Motivated by this ...

Studies have shown that alpha-induced nuclear reactions in the hot CNO cycles and on the waiting points of the rp-process play a principal role in energy production and nucleosynthesis on the surface of mass-accreting white dwarfs and neutron stars. This paper will present recent measurements at Notre Dame on the rate of 15O(?,?) and new experiments for ...

We numerically study the long-term evolution of the accretion disc around the neutron star in a coplanar Be/X-ray binary with a short period and a moderate eccentricity. From three-dimensional smoothed particle hydrodynamics simulations, we find that the disc evolves through three distinct phases, each characterized by different mass-accretion patterns. In ...

We implemented sink particles in the Adaptive Mesh Refinement (AMR) code FLASH to model the gravitational collapse and accretion in turbulent molecular clouds and cores. Sink particles are frequently used to measure properties of star formation in numerical simulations, such as the star formation rate and efficiency, and the mass distribution of stars. We ...

We develop here a new procedure within Einstein's theory of gravity to generate equilibrium configurations that result as the final state of gravitational collapse from regular initial conditions. As a simplification, we assume that the collapsing fluid is supported only by tangential pressure. We show that the equilibrium geometries generated by this ...

Some of the main problems in the theory of the origin and evolution of the solar system are discussed. Consideration is given to the formation and evolution of interstellar clouds the collapse of certain types of such clouds into protostars the formation of planets around some of these stars the formation of satellites around some of the planets and the formation of small ...

The birth of a solar system is enshrouded in gas and dust. A collapsing rotating cloud increases in density until a critical point is reached and a YOUNG STELLAR OBJECT begins its rapid accretion at the center, still surrounded by a disk of gas and dust (figure 1). As stars evolve through a T-Tauri phase, much of this primordial dust cloud is removed by ...

We calculate the evolution of zero-metallicity Population III (Pop III) stars whose mass grows from the initial mass of approx1 M{sub sun} by accreting the surrounding gases. Our calculations cover whole evolutionary stages from the pre-main sequence, via various nuclear burning stages, through the final core-collapse or pair-creation instability phases. ...

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