Zwart, Simon F. Portegies, Chen, Hui-Chen
We 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...
A dynamical origin for early mass segregation in young star clusters (2006)
McMillan, Stephen L.W., Vesperini, Enrico, Zwart, Simon F. Portegies
Some 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...
Disruption time scales of star clusters in different galaxies (2004)
Gieles, Mark, Zwart, Simon F. Portegies
The observed average lifetime of the population of star clusters in the Solar Neighbourhood, the Small Magellanic Cloud and in selected regions of M51 and M33 is compared with simple theoretical...
Ultraluminous X-ray Sources as Intermediate Mass Black Holes Fed by Tidally Captured Stars (2003)
Hopman, Clovis, Zwart, Simon F. Portegies, Alexander, Tal
The 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...
The efficiency of the spiral-in of a black hole to the Galactic centre (2002)
Spinnato, Piero F., Fellhauer, Michael, Zwart, Simon F. Portegies
We study the efficiency at which a black hole or dense star cluster spirals-in to the Galactic centre. This process takes place on a dynamical friction time scale, which depends on the value of the...
The runaway growth of intermediate-mass black holes in dense star clusters (2002)
Zwart, Simon F. Portegies, McMillan, Steve L. W.
We 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...
Runaway Collisions in Star Clusters (2000)
Zwart, Simon F. Portegies, Makino, Junichiro, McMillan, Stephen L. W., Hut, Piet
We 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...
The population of close double white dwarfs in the Galaxy (2000)
Yungelson, Lev, Nelemans, Gijs, Zwart, Simon. F. Portegies, Verbunt, Frank
We 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...
Population synthesis for double white dwarfs I.Close detached systems (2000)
Nelemans, Gijs, Yungelson, Lev R., Zwart, Simon F. Portegies, Verbunt, Frank
We model the population of double white dwarfs in the Galaxy and find a better agreement with observations compared to earlier studies, due to two modifications. The first is the treatment of the...
Is the Galactic center populated with young star clusters? (2000)
We 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...
Reconstructing the evolution of double helium white dwarfs: envelope loss without spiral-in (2000)
Nelemans, Gijs, Verbunt, Frank, Yungelson, Lev R., Zwart, Simon F. Portegies
The unique core-mass - radius relation for giants with degenerate helium cores enables us to reconstruct the evolution of three observed double helium white dwarfs with known masses of both...
Zwart, Simon F. Portegies, Bhattacharya, Dipankar, Kaper, Lex
The recent finding by Chevalier & Ilovaisky (1998) that OB-supergiant X-ray binaries have relatively large runaway velocities whereas Be/X-ray binaries have low runaway velocities, provides...
Star cluster ecology IVa: Dissection of an open star cluster---photometry (2000)
Zwart, Simon F. Portegies, McMillan, Stephen L. W., Hut, Piet, Makino, Junichiro
The evolution of star clusters is studied using N-body simulations in which the evolution of single stars and binaries are taken self-consistently into account. Initial conditions are chosen to...
We 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...
Gravitational waves from cosmological compact binaries (2000)
Schneider, Raffaella, Ferrari, Valeria, Matarrese, Sabino, Zwart, Simon F. Portegies
We 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...
The Evolution of Globular Clusters in the Galaxy (1999)
Takahashi, Koji, Zwart, Simon F. Portegies
We 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,...
Gamma-ray bursts and density evolution of neutron star binary mergers (1998)
Bagot, Philippe, Zwart, Simon F. Portegies, Yungelson, Lev R.
The evolution of the comoving cosmic merger-rate density of neutron star binaries n_c(z) is calculated using a distribution of their merging times provided by population-synthesis computations of...
Evolution of Close Binaries: Formation and Merger of Neutron Star Binaries (1998)
Yungelson, Lev, Zwart, Simon F. Portegies
We 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...
Formation and Evolution of Binary Neutron Stars (1997)
Zwart, Simon F. Portegies, Yungelson, Lev R.
The 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...
Stellar Evolution and Dynamics in Star Clusters (1997)
Zwart, Simon F. Portegies, Tout, Christopher A., Lee, Hyung Mok
Dynamical models of star clusters are maturing in the sense that effects other than simple point particle dynamics are taken into account. We summarize the relevance of and prospects for this new...
Formation of Low-mass Black Hole X-ray Transients (1997)
Zwart, Simon F. Portegies, Verbunt, Frank, Ergma, Ene
We 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...
Star Cluster Ecology II: Binary evolution with single-star encounters (1997)
Zwart, Simon F. Portegies, Hut, Piet, McMillan, Stephen L. W., Verbunt, Frank
Three-body effects greatly complicate stellar evolution. We model the effects of encounters of binaries with single stars, based on parameters chosen from conditions prevalent in the cores of...
Star Cluster Ecology I: A Cluster Core with Encounters between Single Stars (1997)
Zwart, Simon F. Portegies, Hut, Piet, Verbunt, Frank
Star 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...
The formation of black-holes in low-mass X-ray binaries (1997)
Zwart, Simon F. Portegies, Verbunt, Frank, Ergma, Ene
We 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...