Results for "Simon Portegies Zwart"

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Numerical verification of the microscopic time reversibility of Newton's equations of motion: Fighting exponential divergenceFeb 03 2018Numerical solutions to Newton's equations of motion for chaotic self gravitating systems of more than 2 bodies are often regarded to be irreversible. This is due to the exponential growth of errors introduced by the integration scheme and the numerical ... More
The fragility of planetary systemsApr 23 2015We specify the range to which perturbations penetrate a planetesimal system. Such perturbations can originate from massive planets or from encounters with other stars. The latter can have an origin in the star cluster in which the planetary system was ... More
The formation and dynamical evolution of young star clustersNov 30 2015Recent observations have revealed a variety of young star clusters, including embedded systems, young massive clusters, and associations. We study the formation and dynamical evolution of these clusters using a combination of simulations and theoretical ... More
McScatter: a Simple Three-Body Scattering Package with Stellar EvolutionApr 13 2006We describe a simple computer package which illustrates a method of combining stellar dynamics with stellar evolution. Though the method is intended for elaborate applications (especially the dynamical evolution of rich star clusters) it is illustrated ... More
The signatures of the parental cluster on field planetary systemsNov 03 2017Nov 23 2017Due to the high stellar densities in young clusters, planetary systems formed in these environments are likely to have experienced perturbations from encounters with other stars. We carry out direct $N$-body simulations of multi-planet systems in star ... More
A connected component-based method for efficiently integrating multiscale $N$-body systemsJul 26 2014We present a novel method for efficient direct integration of gravitational N-body systems with a large variation in characteristic time scales. The method is based on a recursive and adaptive partitioning of the system based on the connected components ... More
The dynamics of stellar disks in live dark-matter haloNov 30 2017Recent developments in computer hardware and software enables researchers to simulate the self-gravitating evolution of galaxies at a resolution comparable to the actual number of stars. Here we present the results of a series of such simulations. We ... More
The fate of supernova remnants near quiescent supermassive black holesJan 12 2015There is mounting observational evidence that most galactic nuclei host both supermassive black holes (SMBHs) and young populations of stars. With an abundance of massive stars, core-collapse supernovae are expected in SMBH spheres of influence. We develop ... More
Ultraluminous X-ray Sources as Intermediate Mass Black Holes Fed by Tidally Captured StarsDec 23 2003Mar 16 2004The nature of ultraluminous X-ray sources (ULXs) is presently unknown. A possible explanation is that they are accreting intermediate mass black holes (IBHs) that are fed by Roche lobe overflow from a tidally captured stellar companion. We show that a ... More
The formation of black-holes in low-mass X-ray binariesJan 08 1997We calculate the formation rates of low-mass X-ray binaries with a black hole. Both a semi-analytic and a more detailed model predict formation rates two orders of magnitude lower than derived from the observations. Solution of this conundrum requires ... More
A runaway collision in a young star cluster as the origin of the brightest supernovaNov 14 2007Supernova 2006gy in the galaxy NGC 1260 is the most luminous one recorded \cite{2006CBET..644....1Q, 2006CBET..647....1H, 2006CBET..648....1P, 2006CBET..695....1F}. Its progenitor might have been a very massive ($>100$ \msun) star \cite{}, ... More
Are Super-Luminous supernovae and Long GRBs produced exclusively in young dense star clusters?Mar 27 2013Oct 28 2013Super Luminous supernovae (SLSN) occur almost exclusively in small galaxies (SMC/LMC-like or smaller), and the few SLSN observed in larger star-forming galaxies always occur close to the nuclei of their hosts. Another type of peculiar and highly energetic ... More
N-body Integrators with Individual Time Steps from Hierarchical SplittingMay 25 2012We review the implementation of individual particle time-stepping for N-body dynamics. We present a class of integrators derived from second order Hamiltonian splitting. In contrast to the usual implementation of individual time-stepping, these integrators ... More
Capture of exocomets and the erosion of the Oort cloud due to stellar encounters in the GalaxyOct 16 2017The Oort cloud (OC) probably formed more than 4$\,$Gyr ago and has been moving with the Sun in the Galaxy since, exposed to external influences, most prominently to the Galactic tide and passing field stars. Theories suggest that other stars might posses ... More
SiMon: Simulation Monitor for Computational AstrophysicsJun 29 2017Scientific discovery via numerical simulations is important in modern astrophysics. This relatively new branch of astrophysics has become possible due to the development of reliable numerical algorithms and the high performance of modern computing technologies. ... More
The influence of dense gas rings on the dynamics of a stellar disk in the Galactic centerDec 08 2015The Galactic center hosts several hundred early-type stars, about 20% of which lie in the so-called clockwise disk, while the remaining 80% do not belong to any disks. The circumnuclear ring (CNR), a ring of molecular gas that orbits the supermassive ... More
The origin of interstellar asteroidal objects like 1I/2017 U1Nov 09 2017With the recently discovered interstellar object 1I/2017U1 (1I/'Oumuamua) we have to realize that the Solar System is not isolated, but part of a larger environment with which we interact. We compare the kinematics of 1I/2017U1 with simulations of the ... More
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binariesJul 12 2005Cygnus X-3 is a strong X-ray source (L_X about 10^38 erg/s) which is thought to consist of a compact object, accreting matter from a helium star. We find analytically that the estimated ranges of mass-loss rate and orbital-period derivative for Cyg X-3 ... More
Assembly of filamentary void galaxy configurationsJul 26 2013Jul 30 2013We study the formation and evolution of filamentary configurations of dark matter haloes in voids. Our investigation uses the high-resolution LambdaCDM simulation CosmoGrid to look for void systems resembling the VGS_31 elongated system of three interacting ... More
The consequences of a nearby supernova on the early Solar SystemFeb 12 2018If the Sun was born in a relatively compact open cluster (half-mass radius ~3pc) with ~10^3 stars, it is quite likely that a massive (>10MSun) star was nearby when it exploded in a supernova. The repercussions of a supernova can be rather profound, and ... More
Stability of Multiplanetary Systems in Star ClustersJun 12 2017Most stars form in star clusters and stellar associated. To understand the roles of star cluster environments in shaping the dynamical evolution of planetary systems, we carry out direct $N$-body simulations of four planetary systems models in three different ... More
The Ecology of Black Holes in Star ClustersJun 24 2004In this lecture we investigate the formation and evolution of black holes in star clusters. The star clusters under consideration are generally rich, containing more than 10^4 stars, and with a density exceeding 10^4 stars/pc^3. Among these are young ... More
Explaining the light curves of Gamma-ray Bursts with precessing jetsMar 13 1999A phenomenological model is presented to explain the light curves of gamma-ray bursts. Gamma-rays are produced in a narrow beam which sweeps through space due to the precession of a slaved accretion disc. The light curve expected from such a precessing ... More
Planet-Mediated Precision-Reconstruction of the Evolution of the Cataclysmic Variable HU AquariusOct 19 2012Cataclysmic variables (CVs) are binaries in which a compact white dwarf accretes material from a low-mass companion star. The discovery of two planets in orbit around the CV HU Aquarii opens unusual opportunities for understanding the formation and evolution ... More
Stellar disk destruction by dynamical interactions in the Orion Trapezium star clusterNov 28 2015We compare the observed size distribution of circum stellar disks in the Orion Trapezium cluster with the results of $N$-body simulations in which we incorporated an heuristic prescription for the evolution of these disks. In our simulations, the sizes ... More
Collisions in compact star clustersDec 21 1999The high stellar densities in young compact star clusters, such as the star cluster R 136 in the 30 Doradus region, may lead to a large number of stellar collisions. Such collisions were recently found to be much more frequent than previous estimates. ... More
The gravitational wave signature of young and dense star clustersOct 22 2004Oct 29 2004Young star clusters are often born with such high stellar densities that stellar collisions play an important role in their further evolution. In such environments the same star may participate in several tens to hundreds of collisions ultimately leading ... More
The characteristics of high velocity O and B stars which are ejected from supernovae in binary systemsMay 01 2000We perform binary population synthesis calculations to study the origin and the characteristics of runaway O and B stars which are ejected by the supernova explosion of the companion star in a binary system. The number of OB runaways can be explained ... More
Is the Galactic center populated with young star clusters?Jun 29 2000We study the evolution and observability of young and compact star clusters near the Galactic center, such as the Arches cluster and the Quintuplet. The star clusters are modeled with a combination of techniques; using direct N-body, integration to calculate ... More
Gamma-ray binaries: stable mass transfer from neutron star to black holeApr 28 1998Jun 10 1998Gamma-ray bursts are characterized by a duration of milliseconds to several minutes in which an enormous amount of radiation is emitted. The origin of these phenomena is still unknown because proposed models fail to explain all the observed features. ... More
A hypervelocity star from the Large Magellanic CloudDec 22 2006Jan 15 2007We study the acceleration of the star HE0437-5439, to hypervelocity and discuss its possible origin in the Large Magellanic Cloud (LMC). The star has a radial velocity of 723 km/s and is located at a distance of 61 kpc from the Sun. With a mass of about ... More
Merger rates of black hole binaries: prospects for gravitational wave detectorsDec 01 1999Mergers of black-hole binaries are expected to release large amounts of energy in the form of gravitational radiation. However, binary evolution models predict merger rates too low to be of observational interest. In this paper we explore the possibility ... More
A debris disk under the influence of a wide planetary mass companion: The system of HD106906Apr 22 2015The 13 Myr old star HD106906 is orbited by a debris disk of at least 0.067 M_Moon with an inner and outer radius of 20 AU and 120 AU, respectively, and by a planet at a distance of 650 AU. We use this curious combination of a close low-mass disk and a ... More
The possible companions of young radio pulsarsApr 22 1999May 19 1999We discuss the formation of pulsars with massive companions in eccentric orbits. We demonstrate that the probability for a non-recycled radio pulsar to have a white dwarf as a companion is comparable to that of having an old neutron star as a companion. ... More
The Effect of Many Minor Mergers on the Size Growth of Compact Quiescent GalaxiesJan 28 2013Massive galaxies with a half-mass radius <~ 1kpc are observed in the early universe (z~>2), but not in the local universe. In the local universe similar-mass (within a factor of two) galaxies tend to be a factor of 4 to 5 larger. Dry minor mergers are ... More
Planets in triple star systems--the case of HD188753Sep 26 2005We consider the formation of the recently discovered ``hot Jupiter'' planet orbiting the primary component of the triple star system HD188753. Although the current outer orbit of the triple is too tight for a Jupiter-like planet to have formed and migrated ... More
From Thread to Transcontinental Computer: Disturbing Lessons in Distributed SupercomputingJul 04 2015We describe the political and technical complications encountered during the astronomical CosmoGrid project. CosmoGrid is a numerical study on the formation of large scale structure in the universe. The simulations are challenging due to the enormous ... More
The Origin of OB Runaway StarsNov 15 2011About 20% of all massive stars in the Milky Way have unusually high velocities, the origin of which has puzzled astronomers for half a century. We argue that these velocities originate from strong gravitational interactions between single stars and binaries ... More
Computational Gravitational Dynamics with Modern Numerical AcceleratorsSep 18 2014We review the recent optimizations of gravitational $N$-body kernels for running them on graphics processing units (GPUs), on single hosts and massive parallel platforms. For each of the two main $N$-body techniques, direct summation and tree-codes, we ... More
The distinction between star clusters and associationsOct 08 2010In Galactic studies a distinction is made between (open) star clusters and associations. For barely resolved objects at a distance of several Mpc this distinction is not trivial to make. Here we provide an objective definition by comparing the age of ... More
Simulating young star clusters with primordial binariesNov 08 2004We simulate a cluster of 144179 stars including 13107 primordial hard binaries (10% of the total number of single stars and binary centers of mass), using direct integration of the equations of motion of all stars and binaries and incorporating the effects ... More
Precessing jets interacting with interstellar material as the origin for the light curves of gamma-ray burstsJun 09 2000Aug 17 2001We present an internal shock model with external characteristics for explaining the complicated light curves of gamma-ray bursts. Shocks produce gamma-rays in the interaction between a precessing beam of relativistic particles and the interstellar medium. ... More
On the Reliability of N-body SimulationsNov 24 2014The general consensus in the N-body community is that statistical results of an ensemble of collisional N-body simulations are accurate, even though individual simulations are not. A way to test this hypothesis is to make a direct comparison of an ensemble ... More
A pilgrimage to gravity on GPUsApr 13 2012In this short review we present the developments over the last 5 decades that have led to the use of Graphics Processing Units (GPUs) for astrophysical simulations. Since the introduction of NVIDIA's Compute Unified Device Architecture (CUDA) in 2007 ... More
Gravitational waves from remnants of ultraluminous X-ray sourcesJun 08 2005Oct 13 2005Ultraluminous X-ray sources (ULXs) with X-ray luminosities larger than the Eddington luminosity of stellar mass objects may be powered by intermediate mass black holes (IBHs) of masses Mbh~10^3Msun. If IBHs form in young dense stellar clusters, they can ... More
Stellar Collisions and Black Hole Formation in Dense Star ClustersDec 24 2004Close encounters and physical collisions between stars in young dense clusters may lead to the formation of very massive stars and black holes via runaway merging. We examine critically some details of this process, using N-body simulations and simple ... More
The fate of star clusters near the Galactic center I: Analytic considerationsApr 01 2003A star cluster in a galactic nucleus sinks toward the galactic center due to dynamical friction. As it spirals inward, the cluster loses mass due to stellar evolution, relaxation driven evaporation, and tidal stripping, eventually dissolving in the galactic ... More
Black hole mergers in the universeOct 04 1999Nov 30 1999Mergers of black-hole binaries are expected to release large amounts of energy in the form of gravitational radiation. However, binary evolution models predict merger rates too low to be of observational interest. In this paper we explore the possibility ... More
An Inverse Problem Approach to Cluster DynamicsJun 04 2004We propose a new non-parametric algorithm that can be implemented to study and characterize stellar clusters. The scheme attempts to simultaneously recover the stellar distribution function and the cluster potential by using projected radii and velocity ... More
The evolution of binary star clusters and the nature of NGC2136/NGC2137Sep 03 2006We study the evolution of bound pairs of star clusters by means of direct N-body simulations. Our simulations include mass loss by stellar evolution. The initial conditions are selected to mimic the observed binary star cluster NGC 2136 and NGC 2137 in ... More
On the minimal accuracy required for simulating self-gravitating systems by means of direct N-body methodsFeb 26 2014The conservation of energy, linear momentum and angular momentum are important drivers for our physical understanding of the evolution of the Universe. These quantities are also conserved in Newton's laws of motion under gravity \citep{Newton:1687}. Numerical ... More
The disruption of globular star clusters in the galaxy: A comparative analysis between Fokker-Planck and N-body modelsMay 25 1998Recent N-body simulations have shown that there is a serious discrepancy between the results of the N-body simulations and the results of Fokker-Planck simulations for the evolution of globular and rich open clusters under the influence of the galactic ... More
On the Origin of the most massive stars around R136Jan 26 2005We discuss the signature of a peculiar constellation of very massive stars at a projected distance of 2-3 pc around R136a. We discuss various scenarios for its possible origin, such as independent clusters, triggered star formation, supernovae, and ejections ... More
Detecting Irregular Orbits in Gravitational N-body SimulationsJul 14 2006We present a qualitative diagnostic based on the continuous wavelet transform, for the detection of irregular behavior in time series of particle simulations. We apply the method to three qualitatively different gravitational 3-body encounters. The intrinsic ... More
Evolution of Close Binaries: Formation and Merger of Neutron Star BinariesJan 14 1998We discuss the formation and evolution of binaries which contain neutron stars or black holes. It is shown that in a stellar system which for $10^{10}$ yr had star formation rate similar to the current one in the Galactic disc, the rate of neutron star ... More
Young massive star clustersFeb 09 2010Young massive clusters are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. ... More
Observational Constraints on Kicks in SupernovaeSep 22 1997The absence or presence of extremely wide binaries with a radio pulsar and an optical counterpart imposes a strong constraint on the existence and magnitude of kicks in supernova explosions. We search for such systems by comparing the positions of radio ... More
Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis modelAug 31 2012The study of Type Ia supernovae (SNIa) has lead to greatly improved insights into many fields in astrophysics, however a theoretical explanation of the origin of these events is still lacking. We investigate the potential contribution to the SNIa rate ... More
The origin of single radio pulsarsFeb 11 1999By comparing relative rates of supernovae versus formation rates of single radio pulsars, recycled pulsars, binary pulsars and X-ray binaries we put strong limits on the progenitors of radio pulsars and on the requirement of an asymmetry in the supernova. ... More
Sapporo2: A versatile direct $N$-body libraryOct 14 2015Astrophysical direct $N$-body methods have been one of the first production algorithms to be implemented using NVIDIA's CUDA architecture. Now, almost seven years later, the GPU is the most used accelerator device in astronomy for simulating stellar systems. ... More
Star Cluster Ecology: VII The evolution of young dense star clusters containing primordial binariesJul 20 2006Sep 27 2006We study the first 100Myr of the evolution of isolated star clusters initially containing 144179 stars, including 13107 (10%) primordial hard binaries. Our calculations include the effects of both stellar and binary evolution. Gravitational interactions ... More
On the onset of runaway stellar collisions in dense star clusters - II. Hydrodynamics of three-body interactionsApr 06 2009The onset of runaway stellar collisions in young star clusters is more likely to initiate with an encounter between a binary and a third star than between two single stars. Using the initial conditions of such three-star encounters from direct $N$-body ... More
Secular dynamics of hierarchical multiple systems composed of nested binaries, with an arbitrary number of bodies and arbitrary hierarchical structure. First applications to multiplanet and multistar systemsNov 03 2015Jun 09 2016We present a method for studying the secular gravitational dynamics of hierarchical multiple systems consisting of nested binaries, which is valid for an arbitrary number of bodies and arbitrary hierarchical structure. We derive the Hamiltonian of the ... More
Monte-Carlo Simulations of Globular Cluster Evolution - I. Method and Test CalculationsSep 07 1999Dec 27 1999We present a new parallel supercomputer implementation of the Monte-Carlo method for simulating the dynamical evolution of globular star clusters. Our method is based on a modified version of Henon's Monte-Carlo algorithm for solving the Fokker-Planck ... More
Short gamma-ray bursts from binary neutron star mergers in globular clustersDec 30 2005The first locations of short gamma-ray bursts (GRBs) in elliptical galaxies suggest they are produced by the mergers of double neutron star (DNS) binaries in old stellar populations. Globular clusters, where the extreme densities of very old stars in ... More
High Performance Direct Gravitational N-body Simulations on Graphics Processing UnitsFeb 23 2007We present the results of gravitational direct $N$-body simulations using the commercial graphics processing units (GPU) NVIDIA Quadro FX1400 and GeForce 8800GTX, and compare the results with GRAPE-6Af special purpose hardware. The force evaluation of ... More
A dozen colliding wind X-ray binaries in the star cluster R136 in the 30Doradus regionJun 06 2001Apr 09 2002We analyzed archival Chandra X-ray observations of the central portion of the 30 Doradus region in the Large Magellanic Cloud. The image contains 20 X-ray point sources with luminosities between $5 \times 10^{32}$ and $2 \times 10^{35}$ erg s$^{-1}$ (0.2 ... More
Detecting gravitational waves from the galactic center with Pulsar TimingJan 09 2014Black holes orbiting the Super Massive Black Hole (SMBH) Sgr A* in the Milky-way galaxy center (GC) generate gravitational waves. The spectrum, due to stars and black holes, is continuous below 40 nHz while individual BHs within about 200 AU of the central ... More
Mapping the Galactic Center with Gravitational Wave Measurements using Pulsar TimingOct 27 2011Mar 30 2012We examine the nHz gravitational wave (GW) foreground of stars and black holes (BHs) orbiting SgrA* in the Galactic Center. A cusp of stars and BHs generates a continuous GW spectrum below 40 nHz; individual BHs within 1 mpc to SgrA* stick out in the ... More
Gravitational tree-code on graphics processing units: implementation in CUDAMay 28 2010We present a new very fast tree-code which runs on massively parallel Graphical Processing Units (GPU) with NVIDIA CUDA architecture. The tree-construction and calculation of multipole moments is carried out on the host CPU, while the force calculation ... More
The origin of IRS 16: dynamically driven inspiral of a dense star cluster to the Galactic center?Mar 27 2003Apr 01 2003We use direct N-body simulations to study the inspiral and internal evolution of dense star clusters near the Galactic center. These clusters sink toward the center due to dynamical friction with the stellar background, and may go into core collapse before ... More
Reconstructing the Initial Relaxation Time of Young Star Clusters in the Large Magellanic CloudOct 23 2006We reconstruct the initial two-body relaxation time at the half mass radius for a sample of young $\aplt 300$ Myr star clusters in the large Magellanic cloud. We achieve this by simulating star clusters with 12288 to 131072 stars using direct $N$-body ... More
Ejection of Hyper-Velocity Stars from the Galactic Centre by Intermediate-Mass Black HolesJul 19 2006We have performed N-body simulations of the formation of hyper-velocity stars (HVS) in the centre of the Milky Way due to inspiralling intermediate-mass black holes (IMBHs). We considered IMBHs of different masses, all starting from circular orbits at ... More
Formation and Evolution of Binary Neutron StarsOct 30 1997The formation and evolution of binaries which contain two neutron stars or a neutron star with a black hole are discussed in detail. The evolution of the distributions in orbital period and eccentricity for neutron star binaries are studied as a function ... More
Probing the formation of planetesimals in the Galactic Centre using Sgr A* flaresOct 21 2014Flares in X-ray and near infrared are observed above the quiescent emission of the supermassive black hole (SBH) in the Galactic Centre (GC) at a rate of approximately once per day. One proposed energy source for these flares is the tidal disruption of ... More
White dwarf pollution by planets in stellar binariesJul 05 2016Approximately $0.2 \pm 0.2$ of white dwarfs (WDs) show signs of pollution by metals, which is likely due to the accretion of tidally disrupted planetary material. Models invoking planet-planet interactions after WD formation generally cannot explain pollution ... More
New population synthesis model: Preliminary results for close double white dwarf populationsJan 14 2011Feb 07 2011An update is presented to the software package SeBa for simulating single star and binary evolution in which new stellar evolution tracks have been implemented. SeBa is applied to study the population of close double white dwarf and the delay time distribution ... More
The Evolution of Globular Clusters in the GalaxyMar 24 1999Jan 11 2000We investigate the evolution of globular clusters using N-body calculations and anisotropic Fokker-Planck (FP) calculations. The models include a mass spectrum, mass loss due to stellar evolution, and the tidal field of the parent galaxy. Recent N-body ... More
MPWide: a light-weight library for efficient message passing over wide area networksDec 03 2013We present MPWide, a light weight communication library which allows efficient message passing over a distributed network. MPWide has been designed to connect application running on distributed (super)computing resources, and to maximize the communication ... More
High performance cosmological simulations on a grid of supercomputersSep 26 2011We present results from our cosmological N-body simulation which consisted of 2048x2048x2048 particles and ran distributed across three supercomputers throughout Europe. The run, which was performed as the concluding phase of the Gravitational Billion ... More
GPU-Enabled Particle-Particle Particle-Tree Scheme for Simulating Dense Stellar Cluster SystemJun 15 2015We describe the implementation and performance of the ${\rm P^3T}$ (Particle-Particle Particle-Tree) scheme for simulating dense stellar systems. In ${\rm P^3T}$, the force experienced by a particle is split into short-range and long-range contributions. ... More
SAPPORO: A way to turn your graphics cards into a GRAPE-6Feb 25 2009Mar 05 2009We present Sapporo, a library for performing high-precision gravitational N-body simulations on NVIDIA Graphical Processing Units (GPUs). Our library mimics the GRAPE-6 library, and N-body codes currently running on GRAPE-6 can switch to Sapporo by a ... More
Bonsai: A GPU Tree-CodeApr 10 2012We present a gravitational hierarchical N-body code that is designed to run efficiently on Graphics Processing Units (GPUs). All parts of the algorithm are executed on the GPU which eliminates the need for data transfer between the Central Processing ... More
High Performance Direct Gravitational N-body Simulations on Graphics Processing Unit I: An implementation in CgFeb 02 2007Apr 23 2007We present the results of gravitational direct $N$-body simulations using the commercial graphics processing units (GPU) NVIDIA Quadro FX1400 and GeForce 8800GTX, and compare the results with GRAPE-6Af special purpose hardware. The force evaluation of ... More
Life and Death of Young Dense Star Clusters near the Galactic CenterMar 05 2004We discuss the structural change and degree of mass segregation of young dense star clusters within about 100pc of the Galactic center. In our calculations, which are performed with GRAPE-6, the equations of motion of all stars and binaries are calculated ... More
Intermediate Mass Black Holes in Accreting Binaries: Formation, Evolution and Observational AppearanceAug 23 2004Nov 01 2004We study the origin of the ultraluminous X-ray source M82-X1 in the nearby starburst galaxy M82. This X-ray source is of particular interest as it is currently the best candidate intermediate mass black hole; it is associated with a 54mHz quasi periodic ... More
A sparse octree gravitational N-body code that runs entirely on the GPU processorJun 09 2011Apr 10 2012We present parallel algorithms for constructing and traversing sparse octrees on graphics processing units (GPUs). The algorithms are based on parallel-scan and sort methods. To test the performance and feasibility, we implemented them in CUDA in the ... More
Three-body encounters in the Galactic centre: the origin of the hypervelocity star SDSS J090745.0+024507Jul 15 2005Hills (1988) predicted that runaway stars could be accelerated to velocities larger than 1000 km/s by dynamical encounters with the supermassive black hole (SMBH) in the Galactic center. The recently discovered hypervelocity star SDSS J090745.0+024507 ... More
Simulations of Dense Stellar Systems with the AMUSE Software ToolkitNov 16 2011We describe AMUSE, the Astrophysical Multipurpose Software Environment, a programming framework designed to manage multi-scale, multi-physics simulations in a hierarchical, extensible, and internally consistent way. Constructed as a collection of individual ... More
The Relation Between the Globular Cluster Mass and Luminosity FunctionsOct 26 2009The relation between the globular cluster luminosity function (GCLF, dN/dlogL) and globular cluster mass function (GCMF, dN/dlogM) is considered. Due to low-mass star depletion, dissolving GCs have mass-to-light (M/L) ratios that are lower than expected ... More
Can precessing jets explain the light curves of Gamma-ray Bursts?Aug 19 1998Feb 27 1999We present a phenomenological model to explain the light curves of gamma-ray bursts. In the model a black hole is orbited by a precessing accretion disc which is fed by a neutron star. Gamma-rays are produced in a highly collimated beam via the Blandford-Znajek ... More
Effects of Primordial Mass Segregation on the Dynamical Evolution of Star ClustersApr 24 2009In this paper we use N-body simulations to study the effects of primordial mass segregation on the early and long-term evolution of star clusters. Our simulations show that in segregated clusters early mass loss due to stellar evolution triggers a stronger ... More
The runaway growth of intermediate-mass black holes in dense star clustersJan 04 2002May 13 2002We study the growth rate of stars via stellar collisions in dense star clusters, calibrating our analytic calculations with direct N-body simulations of up to 65536 stars, performed on the GRAPE family of special-purpose computers. We find that star clusters ... More
The redshift distribution of short gamma-ray bursts from dynamically formed neutron star binariesMar 16 2006Apr 24 2006Short-hard gamma-ray bursts (SHBs) may arise from gravitational wave (GW) driven mergers of double neutron star (DNS) systems. DNSs may be "primordial" or can form dynamically by binary exchange interactions in globular clusters during core-collapse. ... More
The formation of young dense star clusters through mergersMay 07 2012Young star clusters like R136 in the Large Magellanic Cloud and NGC 3603, Westerlund 1, and 2 in the Milky Way are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass ... More
Gravitational waves from cosmological compact binariesFeb 02 2000We consider gravitational waves emitted by various populations of compact binaries at cosmological distances. We use population synthesis models to characterize the properties of double neutron stars, double black holes and double white dwarf binaries ... More
Was the nineteenth century giant eruption of Eta Carinae a merger event in a triple system?Nov 21 2015We discuss the events that led to the giant eruption of Eta Carinae, and find that the mid-nineteenth century (in 1838-1843) giant mass-loss outburst has the characteristics of being produced by the merger event of a massive close binary, triggered by ... More
Core Formation by a Population of Massive RemnantsMar 13 2004Mar 17 2004Core radii of globular clusters in the Large and Small Magellanic Clouds show an increasing trend with age. We propose that this trend is a dynamical effect resulting from the accumulation of massive stars and stellar-mass black holes at the cluster centers. ... More
Formation of Low-mass Black Hole X-ray TransientsOct 02 1997We study the formation of low-mass X-ray binaries with a black hole as accreting object. The performed semi-analytic analysis reveals that the formation rate of black holes in low-mass X-ray binaries is about two orders of magnitude smaller than that ... More
Simulations of stripped core-collapse supernovae in close binariesOct 08 2015We perform smoothed-particle hydrodynamical simulations of the explosion of a helium star in a close binary system, and study the effects of the explosion on the companion star as well as the effect of the presence of the companion on the supernova remnant. ... More