Results for "Simon Portegies Zwart"

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The Formation of Solar System Analogs in Young Star ClustersOct 30 2018The Solar system was once rich in the short-lived radionuclide (SLR) $^{26}$Al\, but deprived in $^{60}$Fe. Several models have been proposed to explain these anomalous abundances in SLRs, but none has been set within a self-consistent framework of the ... 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
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
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
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
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
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
A Triple Origin for Twin Blue Stragglers in Close BinariesJan 30 2019We propose a formation mechanism for twin blue stragglers (BSs) in compact binaries that involves mass transfer from an evolved outer tertiary companion on to the inner binary via a circumbinary disk. We apply this scenario to the observed double BS system ... 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
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
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
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
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
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
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
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
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
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
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
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
On the temporal evolution of the stellar mass function in Galactic clustersMay 25 2010We show that we can obtain a good fit to the present day stellar mass functions (MFs) of a large sample of young and old Galactic clusters in the range 0.1 - 10 Msolar with a tapered power law distribution function with an exponential truncation of the ... More
Simulations of the tidal interaction and mass transfer of a star in an eccentric orbit around an intermediate-mass black hole: the case of HLX-1Oct 07 2015The X-ray source HLX-1 near the spiral galaxy ESO 243-49 is currently the best intermediate-mass black hole candidate. It has a peak bolometric luminosity of $10^{42}$ erg s$^{-1}$, which implies a mass inflow rate of $\sim10^{-4}$ MSun yr$^{-1}$, but ... More
The stellar IMF of Galactic clusters and its evolutionSep 25 2004We show that one can obtain a good fit to the measured main sequence mass function (MF) of a large sample of Galactic clusters (young and old) with a tapered Salpeter power law distribution function with an exponential truncation. The average value of ... 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 lives and deaths of star clusters near the Galactic centerFeb 14 2001Aug 30 2001We study the evolution and observability of young, compact star clusters near the Galactic center, such as the Arches and Quintuplet systems. The clusters are modeled by integrating the equations of motion of all stars while accounting for the internal ... More
How many young star clusters exist in the Galactic center?Aug 30 2000Oct 24 2000We study the evolution and observability of young compact star clusters within about 200pc of the Galactic center. Calculations are performed using direct N-body integration on the GRAPE-4, including the effects of both stellar and binary evolution and ... More
On the dissolution of evolving star clustersMar 09 1998May 09 1998Using direct N-body simulations which include both the evolution of single stars and the tidal field of the parent galaxy, we study the dynamical evolution of globular clusters and rich open clusters. We compare our results with other N-body simulations ... More
A dynamical origin for early mass segregation in young star clustersSep 19 2006Some young star clusters show a degree of mass segregation that is inconsistent with the effects of standard two-body relaxation from an initially unsegregated system without substructure, in virial equilibrium, and it is unclear whether current cluster ... More
N-body simulations of stars escaping from the Orion nebulaJan 22 2004We study the dynamical interaction in which the two single runaway stars AE Aurigae and mu Columbae and the binary iota Orionis acquired their unusually high space velocity. The two single runaways move in almost opposite directions with a velocity greater ... More
The population of close double white dwarfs in the GalaxyNov 13 2000We present a new model for the Galactic population of close double white dwarfs. The model accounts for the suggestion of the avoidance of a substantial spiral-in during mass transfer between a giant and a main-sequence star of comparable mass and for ... More
Star Cluster Ecology I: A Cluster Core with Encounters between Single StarsJan 09 1997Star clusters with a high central density contain an ecological network of evolving binaries, affected by interactions with passing stars, while in turn affecting the energy budget of the cluster as a whole by giving off binding energy. This is the first ... More
The lost siblings of the SunMar 02 2009The anomalous chemical abundances and the structure of the Edgewood-Kuiper belt observed in the solar system constrain the initial mass and radius of the star cluster in which the sun was born to $M\simeq500$ to 3000 \msun and $R\simeq 1$ to 3 pc. When ... More
The early dynamical evolution of cool, clumpy star clustersApr 29 2010Observations and theory both suggest that star clusters form sub-virial (cool) with highly sub-structured distributions. We perform a large ensemble of N-body simulations of moderate-sized (N=1000) cool, fractal clusters to investigate their early dynamical ... More
Secular dynamics of multiplanet systems: implications for the formation of hot and warm Jupiters via high-eccentricity migrationJun 23 2016Dec 15 2016Hot Jupiters (HJs) are Jupiter-like planets that reside very closely to their host star, within $\sim 0.1\,\mathrm{AU}$. Their formation is not well understood. It is generally believed that they cannot have formed in situ, implying that some form of ... More
The cosmic web in CosmoGrid void regionsNov 05 2014We study the formation and evolution of the cosmic web, using the high-resolution CosmoGrid \$\Lambda\$CDM simulation. In particular, we investigate the evolution of the large-scale structure around void halo groups, and compare this to observations of ... More
Runaway Collisions in Star ClustersDec 11 2000We study the occurrence of physical collisions between stars in young and compact star cluster. The calculations are performed on the GRAPE-4 with the starlab software environment which include the dynamical evolution and the nuclear evolution of all ... More
Using the minimum spanning tree to trace mass segregationJan 14 2009We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that of random stars. If mass segregation is present, the MST length of the most massive stars will be ... More
How well do STARLAB and NBODY4 compare? I: Simple modelsFeb 26 2009Feb 27 2009N-body simulations are widely used to simulate the dynamical evolution of a variety of systems, among them star clusters. Much of our understanding of their evolution rests on the results of such direct N-body simulations. They provide insight in the ... More
The effect of giant molecular clouds on star clustersMay 01 2006We study the encounters between stars clusters and giant molecular clouds (GMCs). The effect of these encounters has previously been studied analytically for two cases: 1) head-on encounters, for which the cluster moves through the centre of the GMC and ... More
Binary population synthesis and SNIa ratesFeb 03 2013Despite the significance of type Ia supernovae (SNeIa) in many fields in astrophysics, SNeIa lack a theoretical explanation. We investigate the potential contribution to the SNeIa rate from the most common progenitor channels using the binary population ... More
How well do STARLAB and NBODY compare? II: Hardware and accuracyJan 27 2012Most recent progress in understanding the dynamical evolution of star clusters relies on direct N-body simulations. Owing to the computational demands, and the desire to model more complex and more massive star clusters, hardware calculational accelerators, ... More
High-velocity runaway stars from three-body encountersSep 27 2009We performed numerical simulations of dynamical encounters between hard massive binaries and a very massive star (VMS; formed through runaway mergers of ordinary stars in the dense core of a young massive star cluster), in order to explore the hypothesis ... More
On time-dependent orbital complexity in gravitational N-body simulationsJan 31 2008Feb 02 2008We implement an efficient method to quantify time-dependent orbital complexity in gravitational $N$-body simulations. The technique, which we name DWaTIM, is based on a discrete wavelet transform of velocity orbital time series. The wavelet power-spectrum ... More
Selection of the SIM Astrometric GridJun 28 2002We investigate the choice of stellar population for use as the Astrometric Grid for the Space Interferometry Mission (SIM). SIM depends on the astrometric stability of about 2000 stars, the so called Grid, against which the science measures are referenced. ... 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
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 origin of the two populations of blue stragglers in M30Oct 31 2018We analyze the position of the two populations of blue stragglers in the globular cluster M30 in the Hertzsprung-Russell diagram. Both populations of blue stragglers are brighter than the cluster's turn-off, but one population (the blue blue-stragglers) ... 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
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
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
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
Computational astrophysics for the future: An open, modular approach with agreed standards would facilitate astrophysical discoverySep 07 2018Scientific discovery is mediated by ideas that, after being formulated in hypotheses, can be tested, validated, and quantified before they eventually lead to accepted concepts. Computer-mediated discovery in astrophysics is no exception, but antiquated ... 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
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
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
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
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
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
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
The Signature of a Windy Radio Supernova Progenitor in a Binary SystemNov 27 2018Jan 29 2019Type II supernova progenitors are expected to emit copious amounts of mass in a dense stellar wind prior to the explosion. When the progenitor is a member of a binary, the orbital motion modulates the density of this wind. When the progenitor explodes, ... 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
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
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
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
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
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
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
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
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
Changes in orientation and shape of protoplanetary discs moving through an ambient mediumJul 04 2017Misalignments between the orbital planes of planets and the equatorial planes of their host stars have been observed in our solar system, in transiting exoplanets, and in the orbital planes of debris discs. We present a mechanism that causes such a spin-orbit ... More
Imprint of the merger and ring-down on the gravitational wave background from black hole binaries coalescenceNov 25 2011We compute the gravitational wave background (GWB) generated by a cosmological population of (BH-BH) binaries using hybrid waveforms recently produced by numerical simulations of (BH-BH) coalescence, which include the inspiral, merger and ring-down contributions. ... More
The Primordial Binary Population - I: A near-infrared adaptive optics search for close visual companions to A star members of Scorpius OB2Oct 05 2004We present the results of a near-infrared adaptive optics survey with the aim to detect close companions to Hipparcos members in the three subgroups of the nearby OB association Sco OB2: Upper Scorpius (US), Upper Centaurus Lupus (UCL) and Lower Centaurus ... More
On the Interpretation of the Age Distribution of Star Clusters in the Small Magellanic CloudJun 08 2007We re-analyze the age distribution (dN/dt) of star clusters in the Small Magellanic Cloud (SMC) using age determinations based on the Magellanic Cloud Photometric Survey. For ages younger than 3x10^9 yr the dN/dt distribution can be approximated by a ... 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
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
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
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
Catching a planet: A tidal capture origin for the exomoon candidate Kepler 1625b IOct 25 2018Nov 24 2018The (yet-to-be confirmed) discovery of a Neptune-sized moon around the ~3.2 Jupiter-mass planet in Kepler 1625 puts interesting constraints on the formation of the system. In particular, the relatively wide orbit of the moon around the planet, at ~40 ... 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
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
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
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
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
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
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
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
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
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
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