A multiphysics and multiscale software environment for modeling astrophysical systems (2008)
Zwart, Simon Portegies, McMillan, Steve, Harfst, Stefan, Groen, Derek, Fujii, Michiko
We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling...
A runaway collision in a young star cluster as the origin of the brightest supernova (2007)
Supernova 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...
A parallel gravitational N-body kernel (2007)
Zwart, Simon Portegies, McMillan, Steve, Groen, Derek, Gualandris, Alessia, Sipior, Michael, Vermin, Willem
We describe source code level parallelization for the {\tt kira} direct gravitational $N$-body integrator, the workhorse of the {\tt starlab} production environment for simulating dense stellar...
Distributed N-body Simulation on the Grid Using Dedicated Hardware (2007)
Groen, Derek, Zwart, Simon Portegies, McMillan, Steve, Makino, Jun
We present performance measurements of direct gravitational N -body simulation on the grid, with and without specialized (GRAPE-6) hardware. Our inter-continental virtual organization consists of...
Belleman, Robert G., Bedorf, Jeroen, Zwart, Simon Portegies
We present the results of gravitational direct $N$-body simulations using the Graphics Processing Unit (GPU) on a commercial NVIDIA GeForce 8800GTX designed for gaming computers. The force evaluation...
The present day mass function in the central region of the Arches cluster (2007)
Zwart, Simon Portegies, Gaburov, Evghenii, Chen, Hui-Chen, Gürkan, M. Atakan
We study the evolution of the mass function in young and dense star clusters by means of direct N-body simulations. Our main aim is to explain the recent observations of the relatively flat mass...
High Performance Direct Gravitational N-body Simulations on Graphics Processing Units (2007)
Zwart, Simon Portegies, Belleman, Robert, Geldof, Peter
We 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...
Zwart, Simon Portegies, Belleman, Robert, Geldof, Peter
We 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...
A hypervelocity star from the Large Magellanic Cloud (2006)
Gualandris, Alessia, Zwart, Simon Portegies
We 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...
The evolution of binary star clusters and the nature of NGC2136/NGC2137 (2006)
Zwart, Simon Portegies, Rusli, Stephanie
We 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...
The MODEST questions: challenges and future directions in stellar cluster research (2006)
Davies, Melvyn B., Amaro-Seoane, Pau, Bassa, Cees, Dale, Jim, De Angeli, Francesca, Freitag, Marc, ...
We present a review of some of the current major challenges in stellar cluster research, including young clusters, globular clusters, and galactic nuclei. Topics considered include: primordial mass...
Performance Analysis of Direct N-Body Algorithms on Special-Purpose Supercomputers (2006)
Harfst, Stefan, Gualandris, Alessia, Merritt, David, Spurzem, Rainer, Zwart, Simon Portegies, Berczik, Peter
Direct-summation N-body algorithms compute the gravitational interaction between stars in an exact way and have a computational complexity of O(N^2). Performance can be greatly enhanced via the use...
Ejection of Hyper-Velocity Stars from the Galactic Centre by Intermediate-Mass Black Holes (2006)
Baumgardt, Holger, Gualandris, Alessia, Zwart, Simon Portegies
We 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...
The formation of higher-order hierarchical systems in star clusters (2006)
Berk, Jelle Van Den, Zwart, Simon Portegies, McMillan, Steve
We simulate open clusters containing up to 182 stars initially in the form of singles, binaries and triples. Due to the high interaction rate a large number of stable quadruples, quintuples,...
Zwart, Simon Portegies, McMillan, Steve, Makino, Jun
We 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...
Detecting Irregular Orbits in Gravitational N-body Simulations (2006)
Gemmeke, Jort, Zwart, Simon Portegies, Kruip, Chael
We 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...
Diffuse, Non-Thermal X-ray Emission from the Galactic Star Cluster Westerlund 1 (2006)
Muno, Michael P., Law, Casey, Clark, J. Simon, Dougherty, Sean M., De Grijs, Richard, Zwart, Simon Portegies, ...
We present the diffuse X-ray emission identified in Chandra observations of the young, massive Galactic star cluster Westerlund 1. After removing point-like X-ray sources down to a completeness limit...
McScatter: a Simple Three-Body Scattering Package with Stellar Evolution (2006)
Heggie, Douglas C., Zwart, Simon Portegies, Hurley, Jarrod
We 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...
Hopman, Clovis, Guetta, Dafne, Waxman, Eli, Zwart, Simon Portegies
Short-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...
McScatter : a simple three-body scattering package with stellar evolution (2006)
Heggie, Douglas C., Zwart, Simon Portegies, Hurley, Jarrod R.
We 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...
McScatter : a simple three-body scattering package with stellar evolution (2006)
Heggie, Douglas C., Zwart, Simon Portegies, Hurley, Jarrod R.
We 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...
Short gamma-ray bursts from binary neutron star mergers in globular clusters (2005)
Grindlay, Jonathan, Zwart, Simon Portegies, McMillan, Stephen
The 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...
The ecology of star clusters and intermediate mass black holes in the Galactic bulge (2005)
Zwart, Simon Portegies, Baumgardt, Holger, McMillan, Stephen L. W., Makino, Junichiro, Hut, Piet, Ebisuzaki, Toshi
We simulate the inner 100pc of the Milky-Way Galaxy to study the formation and evolution of the population of star clusters and intermediate mass black holes. For this study we perform extensive...
Planets in triple star systems--the case of HD188753 (2005)
Zwart, Simon Portegies, McMillan, Steve
We 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...
Gualandris, Alessia, Zwart, Simon Portegies, Sipior, Michael
Hills (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...
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries (2005)
Lommen, Dave, Yungelson, Lev, Heuvel, Ed Van Den, Nelemans, Gijs, Zwart, Simon Portegies
Cygnus 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...
Gravitational waves from remnants of ultraluminous X-ray sources (2005)
Hopman, Clovis, Zwart, Simon Portegies
Ultraluminous 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....
Lamers, Henny, Gieles, Mark, Bastian, Nate, Baumgardt, Holger, Kharchenko, Nina, Zwart, Simon Portegies
We present a simple analytical description of the disruption of star clusters in a tidal field, which agrees excellently with detailed N-body simulations. The analytic expression can be used to...
Stellar Collisions and Black Hole Formation in Dense Star Clusters (2004)
McMillan, Stephen, Zwart, Simon Portegies
Close 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...
Gualandris, Alessia, Zwart, Simon Portegies, Tirado-Ramos, Alfredo
We discuss the performance of direct summation codes used in the simulation of astrophysical stellar systems on highly distributed architectures. These codes compute the gravitational interaction...
Simulating young star clusters with primordial binaries (2004)
Zwart, Simon Portegies, McMillan, Steve
We 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...
Black Holes in Massive Star Clusters (2004)
McMillan, Steve, Baumgardt, Holger, Zwart, Simon Portegies, Hut, Piet, Makino, Junichiro
Close encounters and physical collisions between stars in young dense clusters can result in new channels for stellar evolution, and may lead to the formation of very massive stars and black holes...
The gravitational wave signature of young and dense star clusters (2004)
Young 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...
The stellar IMF of Galactic clusters and its evolution (2004)
De Marchi, Guido, Paresce, Francesco, Zwart, Simon Portegies
We 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...
Zwart, Simon Portegies, Dewi, Jasinta, Maccarone, Tom
We 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...
Has the black hole in XTE J1118+480 experienced an asymmetric natal kick? (2004)
Gualandris, Alessia, Colpi, Monica, Zwart, Simon Portegies, Possenti, Andrea
We explore the origin of the Galactic high latitude black hole X-ray binary XTE J1118+480, and in particular its birth location and the magnitude of the kick received by the black hole upon formation...
The Ecology of Black Holes in Star Clusters (2004)
In 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...
An Inverse Problem Approach to Cluster Dynamics (2004)
Chakrabarty, Dalia, Zwart, Simon Portegies
We 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...
Core Formation by a Population of Massive Remnants (2004)
Merritt, David, Piatek, Slawomir, Zwart, Simon Portegies, Hemsendorf, Marc
Core 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...
Dynamics of Intermediate Mass Black Holes in Star Clusters (2004)
Baumgardt, Holger, Zwart, Simon Portegies, McMillan, Steve, Makino, Jun, Ebisuzaki, Toshikazu
We have followed the evolution of multi-mass star clusters containing massive central black holes by N-body simulations on the GRAPE6 computers of Tokyo University. We find a strong cluster expansion...
Life and Death of Young Dense Star Clusters near the Galactic Center (2004)
Zwart, Simon Portegies, McMillan, Stephen, Baumgardt, Holger
We 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...
The formation of massive black holes through collision runaway in dense young star clusters (2004)
Zwart, Simon Portegies, Baumgardt, Holger, Hut, Piet, Makino, Junichiro, McMillan, Stephen
A luminous X-ray source is associated with a cluster (MGG-11) of young stars \~200pc from the center of the starburst galaxy M82. The properties of the X-ray source are best explained by a black hole...
N-body simulations of stars escaping from the Orion nebula (2004)
Gualandris, Alessia, Zwart, Simon Portegies, Eggleton, Peter P.
We 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...
A search for close companions in Sco OB2 (2003)
Kouwenhoven, Thijs, Brown, Anthony, Zinnecker, Hans, Kaper, Lex, Zwart, Simon Portegies, Gualandris, Alessia
Using adaptive optics we study the binary population in the nearby OB association Scorpius OB2. We present the first results of our near-infrared adaptive optics survey among 199 (mainly) A- and...
The fate of star clusters near the Galactic center I: Analytic considerations (2003)
McMillan, Steve, Zwart, Simon Portegies
A 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,...
Zwart, Simon Portegies, McMillan, Steve, Gerhard, Ortwin
We 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...
A Dynamical Model for the Globular Cluster G1 (2003)
Baumgardt, Holger, Makino, Junichiro, Hut, Piet, McMillan, Steve, Zwart, Simon Portegies
We present a comparison between the observational data on the kinematical structure of G1 in M31, obtained with the Hubble WFPC2 and STIS instruments, and the results of dynamical simulations carried...
Star cluster ecology V: Dissection of an open star cluster--spectroscopy (2003)
Zwart, Simon Portegies, Hut, Piet, McMillan, Steve, Makino, Jun
We have modeled in detail the evolution of rich open star clusters such as the Pleiades, Praesepe and Hyades, using simulations that include stellar dynamics as well as the effects of stellar...
Sills, Alison, Deiters, Stefan, Eggleton, Peter P., Freitag, Marc, Giersz, Mirek, Heggie, Douglas C., ...
This is a summary paper of MODEST-2, a workshop held at the Astronomical Institute ‘Anton Pannekoek’ in Amsterdam, 16-17 December 2002. MODEST is a loose collaboration of people...
Sills, Alison, Deiters, Stefan, Eggleton, Peter P., Freitag, Marc, Giersz, Mirek, Heggie, Douglas C., ...
This is a summary paper of MODEST-2, a workshop held at the Astronomical Institute ‘Anton Pannekoek’ in Amsterdam, 16-17 December 2002. MODEST is a loose collaboration of people...
Theory in a Virtual Observatory (2001)
Teuben, Peter, DeYoung, Dave, Hut, Piet, Levy, Stuart, Makino, Jun, McMillan, Steve, ...
During the last couple of years, observers have started to make plans for a Virtual Observatory, as a federation of existing data bases, connected through levels of software that enable rapid...
Missing Link Found? --- The ``runaway'' path to supermassive black holes (2001)
Ebisuzaki, Toshikazu, Makino, Junichiro, Tsuru, Takeshi Go, Funato, Yoko, Zwart, Simon Portegies, Hut, Piet, ...
Observations of stellar kinematics, gas dynamics and masers around galactic nuclei have now firmly established that many galaxies host central supermassive black holes (SMBHs) with masses in the...
A dozen colliding wind X-ray binaries in the star cluster R136 in the 30Doradus region (2001)
Zwart, Simon Portegies, Pooley, Dave, Lewin, Walter
We 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...
The lives and deaths of star clusters near the Galactic center (2001)
Zwart, Simon Portegies, Makino, Junichiro, McMillan, Stephen, Hut, Piet
We 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...
Immersive 4D Interactive Visualization of Large-Scale Simulations (2001)
Teuben, Peter, Hut, Piet, Levy, Stuart, Makino, Jun, McMillan, Steve, Zwart, Simon Portegies, ...
In dense clusters a bewildering variety of interactions between stars can be observed, ranging from simple encounters to collisions and other mass-transfer encounters. With faster and special-purpose...
How many young star clusters exist in the Galactic center? (2000)
Zwart, Simon Portegies, Makino, Junichiro, McMillan, Stephen, Hut, Piet
We 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...
Zwart, Simon Portegies, Totani, Tomonori
We 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...
Collisions in compact star clusters (1999)
The 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...
Merger rates of black hole binaries: prospects for gravitational wave detectors (1999)
Zwart, Simon Portegies, McMillan, Stephen
Mergers 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...
Black hole mergers in the universe (1999)
Zwart, Simon Portegies, McMillan, Stephen
Mergers 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...
Monte-Carlo Simulations of Globular Cluster Evolution - I. Method and Test Calculations (1999)
Joshi, Kriten, Rasio, Frederic, Zwart, Simon Portegies
We 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...
The possible companions of young radio pulsars (1999)
Zwart, Simon Portegies, Yungelson, Lev
We 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...
Explaining the light curves of Gamma-ray Bursts with precessing jets (1999)
A 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...
The origin of single radio pulsars (1999)
Zwart, Simon Portegies, Heuvel, Edward Van Den
By 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...
Star cluster ecology III: Runaway collisions in young compact star clusters (1998)
Zwart, Simon Portegies, Makino, Junichiro, McMillan, Stephen L. W., Hut, Piet
The evolution of young compact star clusters is studied using N-body simulations in which both stellar evolution and physical collisions between stars are taken into account. The initial conditions...
Can precessing jets explain the light curves of Gamma-ray Bursts? (1998)
Zwart, Simon Portegies, Lee, Chang-Hwan, Lee, Hyun Kyu
We 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...
Takahashi, Koji, Zwart, Simon Portegies
Recent 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...
Gamma-ray binaries: stable mass transfer from neutron star to black hole (1998)
Gamma-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...
On the dissolution of evolving star clusters (1998)
Zwart, Simon Portegies, Hut, Piet, Makino, Junichiro, McMillan, Stephen
Using 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...
Observational Constraints on Kicks in Supernovae (1997)
Zwart, Simon Portegies, Kouwenhoven, Marco, Reynolds, Alastair
The 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...