2026 · Astronomy and Astrophysics
Star Cluster Ecology. VIII. Dynamically Forming S-Type and αCentauri-like Systems ↗Open accessStellar, planetary, and galactic studies
Abstract
Approximately half of the field stars in the local neighbourhood are part of binaries. Nevertheless, only sim15%-20% of the detected exoplanets orbit binary or higher-N systems. Previous work has investigated the extent to which binary systems modify planet formation or introduce dynamical instabilities, but only a few papers considered the role of the cluster environment. We analyse the impact of dynamically formed binaries that emerge naturally from various star cluster environments in already established planetary systems. We conducted numerical simulations replicating the star-forming region NGC 1333. Three models were considered, each using identical cluster realisations and simulation parameters. The cluster itself was initially sub-virial and fractally distributed. Model A assumed that planetary systems are initially in mean motion resonance. In model B, the same planetary systems were moved out of resonance, but remained intrinsically stable. Finally, model C removed all planets from the simulation. Ten independent realisations were integrated per model until 30 Myr. Dynamically formed binaries emerged at similar rates in all models, indicating that planets play only a little role in their formation. We also found a higher production rate of wide binaries than reported in previous numerical studies, which we attribute to the sub-virial and sub-clustered initial conditions. S- and binary S-type planetary systems naturally emerged in our simulations, while P-type systems were rare. For model A, the fraction of S- or binary S-type systems is f_ ̊m S =0.02 and f_ ̊m Bin,, S =0.05, respectively. Rogue planets originating from a binary system were ejected with a substantially higher velocity than those around single-planet system. Planet-star collisions and planet capture events occurred disproportionately within binary systems. Finally, several αCentauri-like systems emerged in our simulations, suggesting that the nearest stellar system to the Sun might have a dynamical origin.
2026 · Monthly Notices of the Royal Astronomical Society
Spin–disc misalignment drives periodic accretion and pulse profile asymmetry in X-ray pulsars ↗Open accessFree PDF ↗Astrophysical Phenomena and Observations Abstract
ABSTRACT We investigate magnetospheric accretion in disc-fed X-ray pulsars assuming that the neutron star spin axis is not perpendicular to the disc plane. We focus on X-ray pulsars, where a geometrically thin disc is truncated far from the stellar surface; the channelled part of the accretion flow is expected to be guided by the large-scale dipolar magnetic field after coupling to it near the disc–magnetosphere boundary. Using numerical simulations of plasma motion from the inner disc edge to the neutron star surface, we show that a finite inclination between the disc normal and the stellar spin axis leads to periodic modulation of the mass accretion rate onto the magnetic poles even for a steady mass supply through the disc. This purely geometrical effect arises because stellar rotation changes the orientation of the magnetosphere relative to the disc, producing phase-dependent mass loading of magnetic field lines. The amplitude and shape of the modulation are determined by the system geometry and by the ratio of the stellar spin period to the flow time through the magnetosphere. The resulting variability affects the structure and luminosity of emitting regions near the neutron star surface and leads to asymmetric X-ray pulse profiles. Even without intrinsic asymmetries of the emission regions, this mechanism breaks the time-reversal symmetry expected for stationary accretion and naturally contributes to the observed asymmetry of pulse profiles and phase-resolved spectral features. The effect may also be relevant for ULX pulsars, where intrinsic accretion rate modulation can help preserve strong pulsations in the presence of geometric beaming.
2026 · Astronomy and Astrophysics
Recoiling black holes ↗Open accessAstrophysical Phenomena and Observations
Abstract
Aims. We aim investigate the tidal disruption and gravitational wave events shortly after a massive black hole binary merges in the Galactic centre and the remnant black hole is ejected from the galaxy. Methods. Using computational methods, we simulated black holes of mass M • = 10 5 M ⊙ and 4 × 10 5 M ⊙ embedded in a nuclear star cluster being kicked out with velocities of v k = 300 and 600 km s −1 . Systems were integrated for 0.1 Myr using a fourth-order Hermite scheme. Results. The kick instantaneously repopulates the loss cone, producing a strong burst of tidal disruption events and gravitational wave mergers. The anisotropy in the apsidal orientation of bound stars prolongs this burst phase. Rates increase for a lower v k and a larger M • , and for steeper nuclear star cluster density profiles at the moment of merger. Conclusions. Assuming binary black holes scour a Bahcall-Wolf density profile during coalescence, ejected remnants with a mass between 10 5 ≤ M • [M ⊙ ]≤4 × 10 5 generate observable offset events at a forecasted rate of Ṅ ≲ 290 yr −1 up to redshift z = 3. If at the moment of merger the milliparsec scales of the nuclear star cluster are described by a shallow density profile ( γ = 1), this decreases to Ṅ ≲ 30 yr −1 . The strong dependence on the initial density profile and recoil kick makes observables powerful probes of the nuclear star cluster post-massive black hole binary coalescence, and it provides a test for numerical relativity.
2026 · arXiv (Cornell University) · preprint
Validating direct solvers for Newton's gravitational N-body problem, and the systematic comparison between IEEE floating point and Posits ↗Free copyFree PDF ↗Numerical Methods and Algorithms Abstract
We present a systematic comparison between arbitrary precise arithmetic and integration, IEEE-754 compliant floating point arithmetic (fp16, bfp16, fp32, double precision fp64, and quadruple precision fp128), and two implementations of Posits (type III unum) for solving Newton's chaotic N-body problem. Each implementation is benchmarked with arbitrary precise calculations to objectively evaluate their performance in precision as well as speed. We rely on hardware and compiler implementations for fp64, and software implementations for arbitrary-precision arithmetic and Posits. Half precision arithmetic (fp16, bfp16, and Posits$<16,1>$) are insufficiently precise for solving Newton's equations of motion. Single precision (fp32, and Posits$<32,2>$) could be used for statistical ensemble calculations, but lead to relatively large errors in any individual strong encounter. All 64-bit implementations fp64 as well as Posits (Posits$<64,3>$) experience difficulty in our tests. One of the implementations of Posits (Universal) gives precision comparable to fp64 but is slow (by at least an orders of magnitude compared to fp64 after correcting for the more efficient hardware support for the latter). The other (CPPPosits) has a speed comparable to fp64 but has systematically larger errors (by about an order of magnitude compared to fp64 with excesses exceeding two orders of magnitude). As a consequence, this implementation leads to a systematic drift in the result space and has difficulty resolving close encounters. Posits and fp64 have difficulty when integrating a dynamical system in a moving reference frame; testing Galileo invariancy. In their current implementation, Posits do not seem to be the ideal alternative for fp64 when integrating chaotic or stiff ordinary differential equations, such as Newton's equations of motion.
2026 · Astronomy and Astrophysics
Planet–moon ejections in close stellar encounters ↗Open accessStellar, planetary, and galactic studies
Abstract
Context . Free-floating planet–moon pairs (FFPMs) may form when planetary systems experience close stellar encounters. Aims . We aim to quantify moon-retention probabilities and ejection cross-sections for planets and planet–moon systems subject to close stellar encounters, and to identify the orbital conditions most favorable for forming FFPMs. Methods . We conducted extensive numerical scattering experiments to compute ejection cross-sections on a grid in the orbital separation of the planet ( a p ) and the moon ( a m ), marginalizing over all other initial parameters. The simulations tracked both planetary and lunar fates across a wide range of encounter geometries. Results . FFPM cross-sections depend primarily on the moon’s semi-major axis, a m , decreasing gradually until a sharp drop near a m ∼ 0.45 R H . Planet-only ejection cross-sections instead decline steadily with a p . Moon survival remains near unity for Io-like orbits ( a m = 0.008 R H ) and falls steeply beyond 0.4 R H . Compared with planet–planet scattering, stellar encounters preserve moons more effectively across all separations. Surviving moons at a m ≲ 0.4 R H retain near-circular, low-inclination orbits, while wide-orbit moons show stronger dynamical excitation. Applying our cross-section maps to the microlensing system MOA-2011-BLG-262Lb suggests possible progenitor semi-major axes between a p ∼ 1.3 au and ∼5.9 au for a solar-mass host. Even though uncertainties remain large and the probability distribution is rather flat, we prefer a p ∼ 5.2 au. Conclusions . Stellar encounter ejections constitute a viable channel for producing FFPMs whose orbital and survival properties differ from those formed by planet–planet scattering. Moon retention and orbital excitation patterns provide promising diagnostics of ejection history. Current and upcoming microlensing and direct-imaging surveys may be capable of detecting Galilean-mass exomoons around rogue planets, offering new tests of dynamical formation pathways.
2026 · Astronomy and Astrophysics
The exponential growth of infinitesimal perturbations in the long-term evolution of simulated galaxies ↗Open accessGalaxies: Formation, Evolution, Phenomena
Abstract
Context. Self-gravitating systems of N particles are chaotic. We study how chaotic the Galaxy is, and what the consequences are. Aims. We therefore simulated the dynamical evolution of a galaxy-scale distribution of point masses in order to measure the degree of chaos in such a system. Methods. These calculations were performed using the softened gravitational N -body tree-code Bonsai, with up to 40 million equal-mass particles. Smaller simulations were performed to establish the scaling of the Lyapunov time t L with N . Results. We established the relations between the degree of chaos, the number of particles, and the softening length in the gravitational force calculation of large-scale N -body simulations. The moment in which the bar forms appears to be insensitive to infinitesimal perturbations to the initial realisation. In contrast, the bar strength and its further evolution sensitively depend on these perturbations. Interestingly enough, the maximum in the run-to-run variation in the bar strength is at about the maximum bar strength, and it drops until the bar buckles. The galaxies we simulated are highly chaotic, but the softening in the simulations suppresses chaos. Still, our models show considerable variations in the macroscopic behaviour caused by infinitesimal perturbations to the initial conditions. Real galaxies, however, are expected to be orders of magnitude more chaotic than our simulations, and we are unable to quantify the consequences of this. Smooth galactic potentials for studying individual stellar orbits should be handled with caution on timescales longer than the Lyapunov time. When we extrapolate our results to the number of stars in the Galaxy without planets and other minor bodies, we conclude that Milky Way-size galaxies are chaotic on a timescale of less than a million years.
2026 · arXiv (Cornell University) · preprint
Centrally concentrated star formation in young clusters II: Jet feedback ↗Free copyFree PDF ↗Astrophysics and Star Formation Studies Abstract
Protostellar jets are one of the earliest forms of stellar feedback, but their impact on star formation and cluster assembly in centrally concentrated molecular clouds remains poorly understood. We study how protostellar jets affect the star formation efficiency, the temporal variability of star formation, star cluster structure, and the early dynamical state of centrally concentrated, newly forming star clusters using the Torch star cluster formation framework. We adopt a centrally concentrated initial cloud model with mass M = 2.5 x 10^3 solar masses and compare six pairs of simulations with and without protostellar jets, supplemented by one additional higher resolution pair of simulations. We analyze our simulations using global star formation diagnostics together with structural and dynamical measures of the stellar population. Models with jet feedback achieve star formation efficiencies of 12-16%, while the corresponding models without jets yield higher efficiencies of 19-33%. Jets also cause star formation to occur in discrete bursts rather than continuously, to produce more extended and substructured stellar systems, and to leave behind stellar populations that are less tightly bound and have higher virial parameters. In our centrally concentrated initial conditions, runs with jets form stellar systems that better reproduce the observed range of the projected structural parameter Q_2D in young clusters than runs without jets, indicating that protostellar jets are an important early feedback channel even in centrally concentrated clouds that regulates star formation efficiencies and shapes the emerging cluster structure.
2026 · The Astronomical Journal
Protostellar Jets in Star Cluster Formation and Evolution. I. Implementation and Initial Results ↗Open accessAstrophysics and Star Formation Studies
Abstract
Abstract Stars form in clusters from the gravitational collapse of giant molecular clouds, which is opposed by a variety of physical processes, including stellar feedback. The interplay between these processes determines the star formation rate of the clouds. To study how feedback controls star formation, we use a numerical framework that is optimized to simulate star cluster formation and evolution. This framework, called Torch , combines the magnetohydrodynamical code FLASH with N-body and stellar evolution codes in the Astrophysical Multipurpose Software Environment (AMUSE). Torch includes stellar feedback from ionizing and nonionizing radiation, stellar winds, and supernovae, but, until now, did not include protostellar jets. We present our implementation of protostellar jet feedback within the Torch framework and describe its free parameters. We then demonstrate our new module by comparing cluster formation simulations with and without jets. We find that the inclusion of protostellar jets slows star formation, even in clouds of up to M = 2 × 10 4 M ⊙ . We also find that the star formation rate of our lower-mass clouds ( M = 5 × 10 3 M ⊙ ) is strongly affected by both the inclusion of protostellar jets and the chosen jet parameters, including the jet lifetime and injection velocity. We follow the energy budget for each simulation and find that the inclusion of jets systematically increases the kinetic energy of the gas at early times. The implementation of protostellar jet feedback in Torch opens new areas of investigation regarding the role of feedback in star cluster formation and evolution.
2026 · dataset
Simulation data for "Centrally concentrated star formation in young clusters II: Jet feedback" ↗Astrophysics and Star Formation Studies
Abstract
This package provides the analysis products and raw simulation snapshots accompanying the paper "Centrally concentrated star formation in young clusters II: Jet feedback." It includes time‑history tables, per‑snapshot stellar particle catalogues, raw FLASH/Torch HDF5 snapshots at two reference epochs, and density‑slice movies for 14 hydrodynamic simulations of star cluster formation with and without protostellar jet feedback, spanning three AMR resolution levels.
2026 · The Astrophysical Journal
Life Is But a Stream: The Distribution of Planetary Systems along Stellar Streams and Their Properties ↗Open accessFree PDF ↗Stellar, planetary, and galactic studies Abstract
Abstract The majority of discovered exoplanets have been observed orbiting field stars as opposed to within a star cluster. To determine whether the lack of observed exoplanets in star clusters is due to gravitational perturbations or observational limitations, we consider the possibility of studying exoplanets in stellar streams. We present the results of direct N -body simulations of planetary systems around stars that orbit within a star cluster. Our simulations demonstrate that stars with early cluster escape times tend to retain all their planets as they spend most of their time orbiting in the cluster’s low-density outskirts. Alternatively, stars with later escape times can have a wide range of survival fractions as they are subjected to a range of local densities and encounter types. With respect to the stellar stream that forms as the result of the cluster’s dissolution, stars near the edge of the stream are therefore more likely to have unperturbed planetary systems. Conversely, stars near the center of the stream have a higher chance of having planets pushed to eccentric or inclined orbits, or stripped from the system entirely. From our suite of simulations, we provide an estimate of the probability that a star will host a planet with a given initial semimajor axis a 0 based on the star’s location along a stellar stream Δ ϕ .
2026 · Astronomy and Astrophysics
Oort Cloud ecology ↗Open accessStellar, planetary, and galactic studies
Abstract
Aims . We investigated the influence of cluster environments on asteroids, with particular attention to captured material. Methods . Using numerical methods, we simulated a sub-virial fractally distributed star-forming region and a virialised Plummer-distributed star-forming region. We initialised both models with a virial radius of 0.5 pc and 150 stars. Stellar populations and their corresponding planetary systems are identical between cluster models. Stars initially hosted 500 asteroids, and those with mass M * ≤ 2.0 M ⊙ were also orbited by one to eight planets. We integrated clusters until 30 Myr. Results . The sub-virial fractal cluster exhibits richer dynamics, with asteroids and planets more frequently acquiring high eccentricities and inclinations, along with a larger fraction of captured and rogue objects. Additionally, this cluster configuration has its extreme trans-Neptunian object and Sednoid analogues occupying regions of phase-space in semi-major axis, eccentricity, and inclination commonly frequented by captured asteroids. Although the virialised Plummer model can produce such objects, it is less dynamically active, and the vast majority of asteroids occupying these regions are native rather than captured. Lastly, neither model efficiently forms an Oort Cloud, indicating that Oort Cloud assembly is strongly suppressed in both dynamically hot and more quiescent clusters.
2026 · Astronomy and Astrophysics
Kozai-driven mass loss of the circumbinary disk in D9 in orbit around the supermassive black hole Sgr A* ↗Open accessAstrophysical Phenomena and Observations
Abstract
Context . The supermassive black hole (Sgr A*) in the Galactic center is surrounded by the S-star cluster consisting of young stars on eccentric orbits. Recently, the an S-star binary system, called D9, was found. Its detection was based on periodic emission in Brackett γ (Br γ ). Since Br γ is considered a signature of accretion, this emission could originate from the interaction of a binary and its circumbinary disk. However, due to the gravitational interaction between Sgr A* and the binary, the disk could be short-lived. Aims . We investigated the evolution of the disk around a stellar binary while orbiting Sgr A*. Methods . We used the AMUSE framework for coupling a gravity solver (for the binary and Sgr A*) with a hydrodynamics solver (for the disk). Results . We find that, irrespective of the initial disk inner and outer radii, it eventually settles between 5.2 a in and 0.28 Hill radii of the binary. Here, a in is the semimajor axis of the binary D9. The inclination of the circumbinary disk follows that of the binary, which evolves due to the von Zeipel-Lidov-Kozai (vZLK) mechanism induced by Sgr A*. The mean eccentricity of the disk is approximately in antiphase with the eccentricity evolution of the binary. We find a vZLK timescale of T vZLK ≈ 62.5 kyr, which is two orders of magnitude shorter than the value reported earlier. As a consequence, D9 has undergone multiple vZLK oscillations in its lifetime of 2.7 Myr. We find that the disk shows periodic bursts of mass loss on the vZLK timescale, suggesting that the mass loss itself is in part driven by the vZLK mechanism. Conclusions . The secular evolution observed in both the binary and the disk are consistent with theoretical predictions. We find the disk loses ~7% ± 2% of its mass every vZLK cycle. If we extrapolate this mass loss, the disk will have 1% of its current mass left after another ~4 Myr. D9 will then be ~6.7 Myr old, which is on the same order as the current average age of S cluster members. The vZLK-driven mass loss could therefore explain the absence of Br γ emission from other S cluster members.
2026 · arXiv (Cornell University) · preprint
Oort Cloud Ecology -- IV. Exchanging Asteroids ↗Free copyFree PDF ↗Stellar, planetary, and galactic studies Abstract
Aims. Investigate the influence of cluster environments on asteroids, with special attention towards captured material. Methods. Using numerical methods, a sub-virial fractally distributed star-forming region and a virialised Plummer distributed star-forming region are simulated. Both models are initialised with a virial radius of 0.5pc and 150 stars. Stellar populations and their corresponding planetary systems are identical between cluster models. Stars initially host 500 asteroids and those with mass M_* <= 2.0 MSun are also orbited by 1 - 8 planets. Clusters are integrated until 30 Myr. Results. The sub-virial fractal cluster exhibits richer dynamics, with asteroids and planets more frequently acquiring high eccentricities and inclinations, along with a larger fraction of captured and rogue objects. Additionally, this cluster configuration has its extreme trans-Neptunian object and Sednoid analogues occupy regions of phase-space in semi-major axis, eccentricity and inclination commonly frequented by captured asteroids. Although the virialised Plummer model can produce such objects, by being less dynamically active, the vast majority of asteroids occupying these regions are native rather than captured. Lastly, neither model efficiently form an Oort Cloud, indicating that Oort Cloud assembly is strongly suppressed in both dynamically hot and more quiescent cluster
2026 · Zenodo (CERN European Organization for Nuclear Research) · other
N-body Galaxy Simulation Dataset for Chaos Analysis ↗Free copyGalaxies: Formation, Evolution, Phenomena
Abstract
This dataset contains the numerical simulation outputs presented in “The exponential growth of infinitesimal perturbations in the long-term evolution of simulated galaxies” by Asano & Portegies Zwart (arXiv:2604.12053). The simulations investigate the chaotic nature of self-gravitating N-body galaxy models by comparing reference runs and perturbed runs that differ only by an infinitesimal perturbation in the initial conditions. Each simulation consists of a pair (or ensemble) of runs: Reference run: r_xx_0 Perturbed runs: r_xx_i (i = 1, 2, ...) The perturbed runs are generated by applying a small displacement to a single particle in the initial condition of the reference run, leading to exponential divergence in phase space. List of simulations Run (i=1...3) Number of particles $N$ softening length $\epsilon$ (pc) r_00_0/r_00_i $1\times10^7$ 50.0 r_19_0/r_19_i $1.25\times10^6$ 141.4 r_20_0/r_20_i $2.5\times10^6$ 100.0 r_21_0/r_21_i $5\times10^6$ 70.7 r_xx_0 and r_xx_i (i ≥ 1) represent the reference and perturbed runs, respectively. Stellar particle data only. Data are stored in compressed NumPy binary format (.npz). Arrays have shape $T \times N \times 6$, where $T$ and $N$ are the number of snapshots and particles; the last axis corresponds to 6D phase-space coordinates $(x,y,z,v_x,v_y,v_z)$. Snapshot interval: $1\, \mathrm{kpc}/ (100 \mathrm{km\, s^{−1}}) \approx 9.78 \, \mathrm{Myr}$. Positions and velocities are given in dimensionless N-body units (Hénon 1971). Particle ordering is identical between paired runs, enabling direct comparison. Code examples https://github.com/tetsuroasano/ChaosTASPZ26
2026 · Astronomy and Astrophysics
Nemesis: A multi-scale, multi-physics algorithm for astrophysics ↗Open accessStellar, planetary, and galactic studies
Abstract
Context . Astronomical environments are governed by a complex interplay of physical processes, including gravitational dynamics, radiative transfer, stellar evolution, chemistry, and hydrodynamics. These processes span a vast range of spatial scales, from short-range interactions where intra-particle distances are vital, to cosmological scales. Both of these characteristics make astrophysics a multi-scale, multi-physics discipline. This complexity introduces complications to numerical methods where round-off errors and a wide range of temporal timescales on which processes act can influence the reliability of results and the efficiency of algorithms. Aims . In this work, we present an updated version of the multi-scale, multi-physics algorithm, Nemesis , which makes use of the Astrophysical Multipurpose Software Environment ( AMUSE ). We formally introduce and validate the algorithm. Methods . We ran a suite of simulations to assess its performance in simulating star clusters containing planetary systems, its ability to capture the von Zeipel–Lidov–Kozai effect, and its computational scalability. Results . The Nemesis code yields indistinguishable results on both the global and local scales when compared with the direct N -body code Ph4 . We find the same result when analysing its ability to capture the von Zeipel–Lidov–Kozai effect. When we analyse its computational performance, the wall-clock time scales roughly as t sim ∝ 1/ δt nem , where δt nem represents the time synchronisation between the global and local scales. When we vary the number of planetary systems, the wall-clock time remains unchanged as long as the number of available cores exceeds the number of systems. Beyond this, we find that, at worst, the computational time increases linearly with the number of excess systems. Conclusions . The method introduced here can be used in numerous domains of astronomy, thanks to its flexibility and modularity, from simulating protoplanetary discs in star clusters to binary black holes in the galactic centre.
2026 · Astronomy and Astrophysics
The formation of periodic three-body orbits for Newtonian systems ↗Open accessStellar, planetary, and galactic studies
Abstract
Context. Braids are periodic solutions to the general N-body problem in gravitational dynamics. These solutions seem special and unique but may result from rather usual encounters between four bodies. Aims. We attempted to learn more about the existence of braids in the Galaxy by reverse engineering the interactions in which they formed. Methods. We carried out simulations of self-gravitating systems of N particles using fourth-order integration. We started by constructing the specific braid and subsequently bombard it with a single object. We subsequently studied how frequently the bombarded braid dissolves into four singles, a triple and a single, a binary and two singles, or two binaries. The relative proportion of these events gives us insight into how easy it is to generate a braid through the reverse process. Results. Braids are relatively easily generated from encounters between two binaries or between a triple and a single object, so long as they meet each other, independent of the braid’s stability. We find that three of the explored braids are long-lived and linearly stable against small perturbations, whereas the fourth is unstable and short-lived. The shortest-lived braid appears to be the least stable and the most chaotic. Nonplanar encounters can also lead to braid formation, which, in our experiments, are themselves planar. The parameter space in azimuth and polar angle that leads to braid formation via binary–binary or triple–single encounters is anisotropic, and the distribution has a low fractal dimension. Conclusions. Since ∼9% of our calculations lead to periodic three-body systems, a substantial fraction, braids may be more common than currently assumed. They could easily temporarily exist as a result of multi-body (binary–binary or triple–single) interactions. We do not expect many stable braids to exist for an extensive period of time, but they may be quite common as transients, surviving for tens to hundreds of periodic orbits. We argue that braids are particularly common in relatively shallow-potential background fields, such as the Oort cloud or the Galactic halo. The formation of braids, however, easily leads to collisions between two or more of their constituents. If composed of compact objects, they potentially form interesting targets for gravitational wave detectors.
2026 · Institute of Physics eBooks · book-chapter
Gravitational Dynamics ↗Stellar, planetary, and galactic studies
Abstract
Here, we discuss how to solve relatively simple problems in Newtonian gravity using the monophysics solvers in AMUSE. Aside from the specific applications, this chapter gives an overview of how to perform simple experiments, what to be aware of, and how to address technical and algorithmic issues. This chapter should therefore be read as a general overview of the working of AMUSE with gravity as a focus. Even if you are not interested in gravity, for example, if your research is dominated by problems in radiative transfer or hydrodynamics, this chapter should still be your starting point.
2026 · Institute of Physics eBooks · book-chapter
Expanding and Extending AMUSE ↗Stellar, planetary, and galactic studies
Abstract
Congratulations on reaching the final chapter of this book! In the last several chapters, we have demonstrated how AMUSE can be used to run individual codes and, more importantly, how to couple codes to simulate more complex systems. In this final chapter, we present several examples of advanced strategies for coupling multiple codes trading performance for accuracy, and vice versa. In addition, we explore two tightly coupled physical problems in more depth. In the first example, we explore accretion onto a supermassive black hole from a population of massive stars in orbit around it. In the second, we study the effect of a nearby supernova on a young planetary system with a circumstellar disk. The problems in this chapter require considerable computer resources for high-resolution results, but the examples can be run at lower but acceptable resolution with some patience on a good workstation.
2026 · Institute of Physics eBooks · book-chapter
Stellar Structure and Evolution ↗Stellar, planetary, and galactic studies
Abstract
Stars evolve. From the moment of birth, a star’s internal structure and appearance change with time. Some of these changes occur very slowly and hardly affect the local environment, but others are swift and have far-reaching repercussions. In this chapter, we review the basic evolution of stars and show how relatively simple stellar-evolution calculations can be conducted.
2026 · Institute of Physics eBooks · book-chapter
Advanced Coupling Strategies ↗Advanced Numerical Methods in Computational Mathematics
Abstract
The full potential of AMUSE becomes clear when we couple codes to solve complex multiphysics or multiscale problems. In this chapter, we discuss coupling issues and strategies, and present examples of coupled solutions. Computing requirements increase drastically when running multiphysics problems. As a result, some of the examples presented in this chapter may be quite challenging for a laptop or workstation. Nonlinear coupling strategies lead to new applications and greatly increase the power of the framework. We are only at the brink of discovering the large number of possibilities and the complexities of the coupling strategies it enables. Many of these, however, may be challenging to validate. We discuss some basic and a few more advanced hierarchical coupling strategies.
2026 · Institute of Physics eBooks · book
Astrophysical Recipes (Second Edition) ↗Free to readFree PDF ↗Computational Physics and Python Applications Abstract
Computational astrophysics connects observational data with theoretical models, driven by advances in both telescope technology and computing power. As simulations grow in scale and realism, software must evolve to keep pace. This book introduces AMUSE, a Python-based framework for modular, multi-physics simulations, allowing users to combine solvers and build complex models. The updated edition supports Python 3 and includes new examples in hydrodynamics and planetary systems. It also offers practical guidance for running AMUSE on supercomputers, using SLURM, enabling GPU support, and executing multi-node simulations. With downloadable scripts and reproducible figures, it serves as a comprehensive resource for both beginners and experienced researchers in the field. Key features • Provides an introduction to the fundamentals of computational astrophysics • Second edition is considerably expanded with three new chapters and two appendices • Update throughout to be compatible with Python Version 3 • Includes downloadable source code and python notebooks
2026 · Institute of Physics eBooks · book-chapter
Elementary Coupling Strategies ↗Modeling and Simulation Systems
Abstract
The simplest multiscale or multiphysics coupling strategy is the linear propagation of information from one code to another. In some sense, one code produces the conditions that another code uses to continue the calculation. These couplings are often unidirectional; one code informs another, but there is no back propagation of information. So long as the response from one code to the other is linear, we can refrain from complex code-coupling strategies, as described in the next chapter (Chapter 9). Linear coupling strategies lead to new AMUSE applications without increasing your script’s complexity, while increasing its applicability.
2026 · Institute of Physics eBooks · book-chapter
Hydrodynamics ↗Computational Fluid Dynamics and Aerodynamics
Abstract
Gas and fluid dynamics play an important role in many astrophysical processes. When addressing these physical phenomena, we refer to the collection of solvers by the generic term hydrodynamics. Gas dynamics forms the basis for our understanding of star and planet formation; it drives X-ray sources and accretion onto supermassive black holes, and it dictates the appearance of galaxies. In AMUSE, hydrodynamics is addressed numerically using two quite distinct methods: the Lagrangian formalism with smoothed particles, and Eulerian grid-based finite-volume formalisms. These approaches are complementary. Hybrid approaches that combine the advantages of both methods are also available in AMUSE. Simulating hydrodynamics is an art, but one with a solid mathematical background.
2026 · Institute of Physics eBooks · book-chapter
Radiative Transfer ↗Galaxies: Formation, Evolution, Phenomena
Abstract
Our human perception of the Universe is dominated by electromagnetic radiation. Radiation forms the basis for essentially all astronomical research, including all of the great images reported by observational astronomers. Radiative transport is the foundation for understanding how radiation interacts with matter. Solving the differential equations describing the interaction between radiation and matter is no trivial task. In AMUSE, radiative transfer is addressed numerically using two quite distinct techniques: by photon propagation through a grid, and by Monte Carlo raytracing. These approaches are complementary. In AMUSE, these codes are typically used to determine the temperature and ionization state of the gas. Radiative transfer is expensive in terms of computer time, particularly if the timescales are governed by the hydrodynamics or the gravitational dynamics of the environment.
2026 · Institute of Physics eBooks · book-chapter
Epilogue ↗2026 · Institute of Physics eBooks · book-chapter
Initial Conditions ↗Cosmology and Gravitation Theories
Abstract
Any simulation requires a starting point. We call these the initial conditions. Some initial conditions are simple, some are extraordinarily complex. The simplest ones are often the most interesting, and lead to the clearest understanding of the complex phenomena that follow through calculation. Many final conditions eventually turn into initial conditions for future simulations. In astrophysics, the ultimate initial conditions are probably the beginning of time and the Universe, whatever they were.
2026 · Institute of Physics eBooks · book-chapter
Fundamental Concepts ↗Computational Physics and Python Applications
Abstract
We live in an era of multimessenger astronomy, meaning that various instruments operating at multiple electromagnetic and non-electromagnetic wavelengths cooperate to collect data. In computational astrophysics, we have the concepts of multiscale and Multiphysics modeling, which are the equivalents of multimessenger astronomy. Here, we discuss the fundamental aspects that enable multimessenger computational astrophysics. Fundamental parts include data handling, communication, unit conversion, and scaling.
2026 · RAS Techniques and Instruments
ReLaTS: a reinforcement learning-based method for dynamically determining the coupling time-step in multiscale simulations of self-gravitating systems ↗Open accessStellar, planetary, and galactic studies
Abstract
ABSTRACT Astrophysical simulations frequently address multiscale, multiphysics problems through subsystem decomposition, problem-tailored integration schemes, and coupling on fixed manually set time-scales. Here we introduce ReLaTS, a reinforcement learning framework that dynamically selects the coupling time-step to optimize the trade-off between accuracy and computational cost. We validate ReLaTS on star clusters containing a planetary system, and test the method by varying the number of stars $N_\star$ in the cluster and the number of planets ($N_{\rm planet}$) orbiting one of them. The method finds the optimal coupling time-step that balances speed and accuracy without requiring expert knowledge. In addition, the trained network operates independently of the coupled N-body algorithms, displaying stable performance across a range of setups. We observe that the method is less reliable for cases with infinitesimal masses, as their contribution to the total energy is negligible compared to that of the massive bodies, and the network is not capable of recognizing potential errors generated while integrating them. For long-time integration of large N systems, the error accumulates. The reinforcement learning algorithm, however, manages to keep the energy error below a pre-set threshold. This approach substantially reduces energy errors relative to fixed time-step baselines without substantial additional computational overhead. Once trained, ReLaTS requires no expert tuning and generalizes across diverse astrophysical domains, enabling adaptive multiscale simulations.
2025 · Astronomy and Astrophysics
Resolving white dwarf binaries within globular clusters with LISA ↗Open accessPulsars and Gravitational Waves Research
Abstract
Context . Globular clusters (GCs) around the Milky Way (MW) are expected to host white dwarf (WD) binaries emitting gravitational waves that could be detectable by LISA. Aims . Our aim is to investigate whether LISA has the capacity to resolve WD binaries in GCs well enough in terms of sky location and distance that they can be distinguished from binaries in the MW disc. Methods . We used a sample of 20 of the most massive GCs around the MW and simulated LISA’s sky location and distance measurement errors for WD binaries in these GCs using the software package GWT oolbox . We did this in the context of a model of the LISA-detectable binaries in the MW from the population synthesis code S e B a . Results . We find that for five of the GCs in our sample, binaries in the GC could be easily distinguished from MW disc binaries using the sky location alone; for another five, binaries in the GCs could be distinguished using a combination of LISA’s sky location and distance measurements; and for the final ten, binaries in the GCs could not be distinguished from overlapping MW disc binaries. The results depend strongly on the sky locations of the GCs, with GCs far away from the Galactic plane being easy to resolve, while GCs close to the Galactic centre overlap with many MW disc binaries. The most promising GC with respect to the potential of locating a WD binary that could be resolved to that specific GC (based on sky location and GC mass) is 47 Tucanae.
2025 · arXiv (Cornell University) · preprint
The significance of Halley's Comet in the Bayeux Tapestry ↗Free copyFree PDF ↗Historical Astronomy and Related Studies Abstract
A comet appears in the Bayeux Tapestry between the scene showing the death of the English king Edward the Confessor and the election of his successor, Harold Godwinson. The Tapestry's inscription only refers to this as a star, though we can see from its depiction, shown with a hairy tail, that it is a comet, now known to us as Halleys Comet P1/Halley. Behind the exciting story of the Bayeux Tapestry, however, goes a rich mythological world of intrigue, deceit, the succession of kings, and earlier sightings of the same comet. In historical accounts of many cultures, comets are generally considered portents of change rather than disaster. Here we consider the significance of the Tapestry's comet in the context of the so-called English succession crisis of 1066 with reference to other contemporary accounts of comets. We conclude that although the tapestry's illustration is suggestive and unmistakably Halleys Comet, it is not a priority for its creators to give a precise account of its arrival in the sky, but rather connect it, likely for political reasons, albeit retrospectively, to the sequential events of Edwards death and Harolds coronation. In that, the tapestry's anonymous artists provide a unique telling of its arrival.
2025 · The Astrophysical Journal
Transferring Data from a Voronoi Mesh to an Adaptive Cartesian Grid in Pursuit of Self-consistent Top-down Star Formation ↗Open accessAstrophysics and Star Formation Studies
Abstract
Abstract Unstructured Voronoi mesh simulations offer many advantages for simulating self-gravitating gas dynamics on galactic scales. Adaptive mesh refinement (AMR) can be a powerful tool for simulating the details of star cluster formation and gas dispersal by stellar feedback. Zooming in from galactic to local scales using the star cluster formation simulation package Torch requires transferring simulation data from one scale to the other. Therefore, we introduce VorAMR , a novel computational tool that interpolates data from an unstructured Voronoi mesh to an AMR Cartesian grid. VorAMR is integrated into the Torch package, which integrates the FLASH AMR magnetohydrodynamics code into the Astrophysical Multipurpose Software Environment. VorAMR interpolates data from an AREPO simulation to a FLASH AMR grid using a nearest-neighbor particle scheme, which can then be evolved within the Torch package, representing the first ever transfer of data from a Voronoi mesh to an AMR Cartesian grid. Interpolation from one numerical representation to another results in an error of a few percent in global mass and energy conservation, which could be reduced with higher-order interpolation of the Voronoi cells. We show that the postinterpolation Torch simulation evolves without numerical abnormalities. A preliminary Torch simulation is evolved for 3.22 Myr and compared to the original AREPO simulation over the same time period. We observe similarly distributed star cluster formation between the two simulations. More compact clusters are produced in the Torch simulation as well as 2.3 times as much stellar material as in AREPO , likely due to the differences in resolution.
2025 · New Astronomy
A systematic north-south asymmetry in the steady-state climate of rapidly-rotating oblique water worlds ↗Open accessStellar, planetary, and galactic studies
Abstract
Planetary obliquity (axial tilt) plays an important role in regulating the climate evolution and habitability of water-covered planets. Despite the suspicion of large obliquities in several exoplanetary systems, this phenomenon remains hard to observe directly. We aimed to study the effect of mass, obliquity, and rotation on the steady state climate of water-covered planets. We simulated the climate evolution of such planets with varying obliquities, rotational speed, and mass using a general circulation model (GCM) of intermediate complexity, assuming aqua-planet configurations. High obliquity supports an asymmetry between the equilibrium climatological conditions in the northern and southern hemispheres. The polar temperature ratio deviates further from unity with increasing obliquity and rotation rate. Cloud coverage patterns also shift with obliquity, displaying distinct latitudinal bands and increased cloudiness in the warmer hemisphere. The climate of habitable-zone aqua-planets turns out to be sensitive to changes in obliquity and rotation rate, but are independent of planet mass. Our results highlight the importance of considering these factors when assessing the surface conditions of exoplanets. As a consequence, surface condition asymmetries in water-world exo-planets can be used to infer the planet’s obliquity and rotation rate.
2025 · The Astrophysical Journal
Massive Interacting Binaries Enhance Feedback in Star-forming Regions ↗Open accessAstrophysics and Star Formation Studies
Abstract
Abstract We present a new framework to incorporate feedback from massive interacting binaries in simulations of star cluster formation. Our new feedback model adds binary stellar evolution to the cluster formation code Torch, and couples it in Amuse to the preexisting modules for collisional stellar dynamics, magnetohydrodynamics, and mechanical and radiative feedback. Our model accounts for the effects of mass transfer on the stars’ mass-loss rates, their radiation spectra, and the timing of core-collapse supernovae. It also injects mass lost through nonconservative mass transfer and CE ejection into the interstellar medium (ISM). We demonstrate the use of our feedback model through simulations of isolated binaries in a gaseous medium, and of embedded clusters of massive binaries. Feedback from interacting binaries efficiently couples with the surrounding ISM. It increases the size of H ii regions, increases the kinetic and thermal energy of the gas, and increases the pressure within H ii regions compared to models that use single star stellar evolution. Those differences arise from the ionizing radiation, which increases by 3 orders of magnitude, resulting in H ii regions that expand due to thermal pressure rather than radiation pressure. The effects of stellar dynamics and the gravitational potential of the background gas cause the evolution of individual binaries to deviate from the predictions made by secular evolution, impacting the subsequent feedback from the binary. We conclude that massive interacting binaries are an important source of feedback in cluster-forming regions, and must be considered when studying the emerging timescales of young star clusters.
2025 · dataset
Supplemental data for the methods paper "Protostellar Jets in Star Cluster Formation and Evolution: I. Implementation and Initial Results" ↗Free copyAstrophysics and Star Formation Studies
Abstract
Stars form in clusters from the gravitational collapse of giant molecular clouds, which is opposed by a variety of physical processes, including stellar feedback. The interplay between these processes determines the star formation rate of the clouds. To study how feedback controls star formation, we use a numerical framework that is optimized to simulate star cluster formation and evolution. This framework, called Torch, combines the magnetohydrodynamical code FLASH with N-body and stellar evolution codes in the Astrophysical Multipurpose Software Environment (AMUSE). Torch includes stellar feedback from ionizing and non-ionizing radiation, stellar winds, and supernovae, but, until now, did not include protostellar jets. We present our implementation of protostellar jet feedback within the Torch framework and describe its free parameters. We then demonstrate our new module by comparing cluster formation simulations with and without jets. We find that the inclusion of protostellar jets slows star formation, even in clouds of up to M = 2 × 10^4 M⊙. We also find that the star formation rate of our lower mass clouds (M = 5 × 10^3 M⊙) is strongly affected by both the inclusion of protostellar jets and the chosen jet parameters, including the jet lifetime and injection velocity. We follow the energy budget for each simulation and find that the inclusion of jets systematically increases the kinetic energy of the gas at early times. The implementation of protostellar jet feedback in Torch opens new areas of investigation regarding the role of feedback in star cluster formation and evolution..
2025 · Nature Astronomy
Why wide Jupiter-mass binary objects cannot form ↗Free copyFree PDF ↗Stellar, planetary, and galactic studies 2025 · The Astrophysical Journal
A Resonant Beginning for the Solar System’s Terrestrial Planets ↗Open accessAstro and Planetary Science
Abstract
Abstract In the past two decades, transit surveys have revealed a class of planets with thick atmospheres, sub-Neptunes, that must have completed their accretion in protoplanet disks. When planets form in the gaseous disk, the gravitational interaction with the disk gas drives their migration and results in the trapping of neighboring planets in mean motion resonances, though these resonances can later be broken when the damping effects of disk gas or planetesimals wane. It is widely accepted that the outer solar system gas-giant planets originally formed in a resonant chain, which was later disrupted by dynamical instabilities. Here, we explore whether the early formation of the terrestrial planets in a resonance chain (including Theia) can evolve to the present configuration. Using N-body simulations, we demonstrate that the giant planet instability would also have destabilized the terrestrial resonance chain, triggering Moon-forming giant impacts in 20%–50% of our simulated systems, dependent on the initial resonance architecture. After the instability, the eccentricity and inclination of the simulated planets match their present-day values. Under the proposed scenario, the current period ratio of 3.05 between Mars and Venus, devoid of any special significance in traditional late-formation models, naturally arises as a relic of the former resonance chain.
2025 · The Astrophysical Journal
He Awa Whiria: The Tidal Streams of Interstellar Objects ↗Open accessFree PDF ↗Stellar, planetary, and galactic studies Abstract
Abstract Upcoming surveys are likely to discover a new sample of interstellar objects (ISOs) within the solar system, but questions remain about the origin and distribution of this population within the Galaxy. ISOs are ejected from their host systems with a range of velocities, spreading out into tidal streams, analogous to the stellar streams routinely observed from the disruption of star clusters and dwarf galaxies. We create a simulation of ISO streams orbiting in the Galaxy, deriving a simple model for their density distribution over time. We then construct a population model to predict the properties of the streams in which the Sun is currently embedded. We find that the number of streams encountered by the Sun is quite large, ∼106 or more. However, the wide range of stream properties means that for reasonable future samples of ISOs observed in the solar system, we may see ISOs from the same star (“siblings”), and we are likely to see ISOs from the same star cluster (“cousins”). We also find that ISOs are typically not traceable to their parent star, though this may be possible for ISO siblings. Any ISOs observed with a common origin will come from younger, dynamically colder streams.
2025 · conference-abstract
Nemesis: An Optimised Algorithm for Simulating Planetary Systems in Clusters ↗Open accessStellar, planetary, and galactic studies
Abstract
We introduce a revamped Nemesis, a numerical tool designed to circumvent the multi-scale, multi-physics problem inherent to numerical simulations of planetary systems in star clusters. We validate the algorithm by comparing it against both a 4th-order Hermite and a symplectic N-body code in simulations of a star cluster hosting five planetary systems, including ~1000 asteroids. Nemesis finds indistinguishable orbital parameters of evolved planetary systems when compared to its direct N-body code counterparts. Moreover, energy errors are comparable to symplectic codes and the algorithm reduces computation time by up to several orders of magnitude. Due to its parallelisation, t, the performance gain increases significantly with the number of planetary systems. As a result, preliminary results of an ongoing simulation consisting of ~4600 star cluster (~4500 planetary systems) is shown, focusing on captured planets, rogue planets and collisional events.
2025 · conference-abstract
Streams of interstellar objects ↗Open accessStellar, planetary, and galactic studies
Abstract
Upcoming surveys are likely to discover a new sample of interstellar objects (ISOs) within the Solar System, but questions remain about the origin and distribution of this population within the Galaxy. ISOs are ejected from their host systems with a range of velocities, spreading out into tidal streams. We simulate ISO streams orbiting in the Galaxy, and derive a simple model for their density distribution over time. We then construct a population model to predict the properties of the streams in which the Sun is currently embedded. We find that the number of streams encountered by the Sun is quite large, ~ 106 or more. However, the wide range of stream properties means that for reasonable future samples of ISOs observed in the Solar System, we may see ISOs from the same star ("siblings"), and we are likely to see ISOs from the same star cluster ("cousins"). We also find that ISOs are typically not traceable to their parent star, though this may be possible for ISO siblings. Any ISOs observed with a common origin will come from younger, dynamically colder streams.
2025 · Astronomy and Astrophysics
Ripples spreading across the Galactic disc ↗Open accessStellar, planetary, and galactic studies
Abstract
Context. Gaia data have revealed vertically asymmetric phase-space structures in the Milky Way (MW) disc, such as phase spirals, indicating vertical oscillations. These oscillations exhibit two distinct modes, the bending mode and the breathing mode, associated with one-arm and two-arm phase spirals, respectively. The mechanisms driving these modes remain debated, with both external and internal origins proposed. Aims. With this study, we aim to explore the excitation mechanisms of the bending and breathing modes and their subsequent evolution in the MW disc, focusing on the interplay between direct perturbations from the Sagittarius dwarf galaxy and indirect contributions from tidally induced spiral arms. Methods. We performed high-resolution N-body simulations with five billion particles to model the interaction between an MW-like disc galaxy and a Sagittarius dwarf-like satellite. These simulations resolve fine phase-space structures, enabling analysis of the bending and breathing modes at both macroscopic (global bending and breathing waves) and microscopic (local phase spirals) scales. Results. Our simulations demonstrate that the satellite’s perturbation directly excites the bending mode and induces spiral arms in the Galactic disc. These spiral arms, in turn, excite the breathing mode, making it an indirect consequence of the satellite interaction. Initially, the bending mode dominates, but it rapidly decays due to horizontal mixing. In contrast, the breathing mode persists for a longer duration, sustained by the spiral arms, leading to a transition from a bending-dominated to a breathing-dominated state. This transition progresses faster in the inner galaxy than in the outer galaxy. The simulations successfully reproduce the one-arm phase spiral observed in the solar neighbourhood and reveal two-arm phase spirals, particularly in the inner galaxy, associated with spiral arm-induced breathing modes. The two-arm phase spirals emerge approximately 200–250 Myr after the bending-to-breathing transition. Conclusions. Our findings highlight the combined effects of direct satellite perturbations and indirect spiral arm dynamics in shaping the vertical structure of the MW disc. The emergence of the two-arm phase spiral after the bending-to-breathing transition suggests that the MW disc experienced a significant perturbation more than ∼ 400 Myr ago, likely caused by the Sagittarius dwarf galaxy. This study underscores the importance of considering the dynami
2025 · Astronomy and Astrophysics
Stability of a cluster-disrupted mean-motion resonance (chain) in HR 8799 and PDS 70 ↗Open accessStellar, planetary, and galactic studies
Abstract
Context. HR 8799 is a planetary system in which four observed planets potentially form a mean-motion resonance chain. Although they potentially form a resonance chain, it is not clear from the observations whether they are in mean-motion resonance. Similarly, PDS 70 is a planetary system in which two observed planets are potentially in mean-motion resonance. Aims. We study the stability of HR 8799 and PDS 70 under external perturbations to test how they respond under resonance and under mean-motion resonance. Methods. We integrated the equations of motion of the planets in HR 8799 and PDS 70 beginning with a system either in resonance or in mean-motion resonance and studied the stability of HR 8799 and PDS 70 in isolation and in a star cluster. In the star cluster, we accounted for the effects of passing stars. The dynamics of the star cluster were resolved using the Lonely Planets module in AMUSE. Results. HR 8799 and PDS 70 in mean-motion resonance are stable, whereas in non-resonance they dissolve on timescales of 0.303 ± 0.042 Myr and 1.26 ± 0.25 Myr, respectively. In a cluster, the non-resonant planetary system of HR 8799 is slightly more stable than in isolation but still dissolves on a timescale of 0.300 ± 0.043 Myr, whereas the resonant planetary system remains stable for at least 0.71 Myr. In contrast, the non-resonant planetary system of PDS 70 is approximately as stable in a cluster as in isolation and dissolves on a timescale of 1.03 ± 0.20 Myr, whereas the resonant PDS 70 planetary system remains stable for at least 0.83 Myr. Conclusions. Considering the more stable solutions of mean-motion resonance for HR 8799, we argue that the planetary system was born in mean-motion resonance and that the mean-motion resonance has been preserved. If HR 8799 was not born in resonance, then the probability of its survival until the present day is negligible. Similarly, we argue that the planetary system of PDS 70 was probably born in mean-motion resonance and that the mean-motion resonance has been preserved. We also find it possible for planetary systems with a broken mean-motion resonance chain to survive longer in a perturbing cluster environment than in isolation.
2025 · The Astrophysical Journal
Oort Cloud Formation and Evolution in Star Clusters ↗Open accessFree PDF ↗Stellar, planetary, and galactic studies Abstract
Abstract It is unknown whether an Oort cloud reaches its maximum mass within its star’s birth cluster or millions of years later. Complicating the Oort cloud evolution process is the fact that comets can be stripped from orbit due to perturbations from passing stars. We explore how a star’s cluster escape time (t esc) and the time its Oort cloud reaches maximum mass (t max ) affect the Oort cloud’s ability to survive via N-body simulations. In a 14 M ⊙ pc–3 cluster, we identify 50 stars of 1 M ⊙ with a range of t esc to host Oort clouds, each with 1000 comets at t max . For each host, we consider Oort clouds that reach maximum mass 0, 50, and 250 Myr after the cluster’s formation. Each Oort cloud’s evolution is simulated in the cluster from t max to t esc. Only a fraction of comets tend to remain in orbit, with this amount depending on t max and t esc. We observe that 12%, 22%, and 32% of Oort clouds with a t max of 0, 50, and 250 Myr retain >50% of their comets at t esc, respectively. We find that the fraction of comets stripped has the relationship f = m log 10 t esc − t max Myr , where m = 0.32 ± 0.04, indicating that the longer the Oort cloud remains in the cluster, the more comets are stripped, with this fraction increasing logarithmically at approximately the same rate for each t max .
2025 · Astronomy and Astrophysics
Oort cloud ecology ↗Abstract
Context. The Sun was born in a clustered environment with ≲10 000 other stars. Given it is an isolated star today, the Sun must have left the nest. We do not directly know when that happened, how violent the ejection was, or how far its solar siblings have drifted apart. Aims. The mass of the fragile outer Öpik-Oort cloud (between rinner ∼ 30 000 au and 200 000 au from the Sun) and the orbital distribution of planetesimals in the inner Oort-Hills cloud (between ∼1000 au and ∼30 000 au) are sensitive to the dynamical processes involving the Sun in the parent cluster. We aim to understand the extent to which we can constrain the Sun’s birth environment based on observations of the Oort cloud. Methods. The approach presented in this work was based on a combination of theoretical arguments and N-body simulations. Results. We show that the current mass of the Öpik-Oort cloud (between 0.2 M⊕ and 2.0 M⊕) is best explained by the assumption that the Sun left the nest within ∼20 Myr after the giant planets formed and migrated. Conclusions. As a consequence, a possible dynamical encounter with another star, carving the Kuiper belt, the Sun’s abduction of Sedna, and other perturbations induced by nearby stars then must have taken place shortly after the giant planets in the Solar System formed – but before the Sun left the parent cluster. Signatures of the time the Sun spent in the parent cluster must still be visible in the outer parts of the Solar System even today. The strongest constraints will be the discovery of a population of relatively low-eccentricity (e ≲ 0.9) objects in the inner Oort cloud (but 500 ≲ a ≲ 104 au).
2025 · Physical Review Letters
Origin of the Most Recently Ejected OB Runaway Star from the R136 Cluster ↗Free copyStellar, planetary, and galactic studies
Abstract
The ∼60 000 solar-mass (M_{⊙}) star cluster R136 (NGC 2070) in the Tarantula Nebula in the Large Magellanic Cloud is the host of at least 55 massive stars (M≳10M_{⊙}) which move away from the cluster at projected velocities ≥27.5 km/s. The origin of the high velocities of such runaway stars have been debated since the 1960s, resulting either from dynamical ejections or from supernova explosions. Because of the Gaia satellite's outstanding precision, we can now retrace the most recently ejected binary star, Mel 34, back to the center of R136 and reconstruct the events that 52 000 years ago led to its removal from R136; i.e., we establish its dynamical interaction and ejection history. We find that this ejection requires the participation of five stars in a strong interaction between a triple composed of the tight massive binary Mel 39, orbited by the star VFTS 590, and the binary star Mel 34. The participation of five stars is unexpected because runaway stars were not expected to result from triple interactions. The deterministic nature of the Newtonian dynamics in the scattering enables us to reconstruct the encounter that ejected Mel 34. We then predict that Mel 39 is a binary star with an 80M_{⊙} companion star that orbits within ∼1° in the same plane as Mel 34 and escapes the cluster with a velocity of ∼64 km/s. The five stars will undergo supernova explosions in the coming 5 Myr at a distance of ∼180-332 pc from their birth location (R136). The resulting black hole binaries, however, are not expected to merge within a Hubble time.
2025 · Zenodo (CERN European Organization for Nuclear Research) · dataset
Stability of a cluster-disrupted mean-motion resonance (chain) in HR 8799 and PDS 70 - Data ↗Free copyStellar, planetary, and galactic studies
2025 · Astronomy and Astrophysics
Binary-single interactions with different mass ratios ↗Open accessPulsars and Gravitational Waves Research
Abstract
Context. Dynamical interactions in star clusters are an efficient mechanism to produce the coalescing binary black holes (BBHs) that have been detected with gravitational waves (GWs). Aims. We want to understand how BBH coalescence can occur during – or after – binary-single interactions with different mass ratios. Methods. We perform gravitational scattering experiments of binary-single interactions using different mass ratios of the binary components (q2 ≡ m2/m1 ≤ 1) and the incoming single (q3 ≡ m3/m1). We extract cross-sections and rates for (i) GW capture during resonant interactions; (ii) GW inspiral in between resonant interactions and apply the results to different globular cluster conditions. Results. We find that GW capture during resonant interactions is most efficient if q2 ≃ q3 and that the mass-ratio distribution of BBH coalescence due to inspirals is ∝ m1−1q2.9﹢α, where α is the exponent of the BH mass function. The total rate of GW captures and inspirals depends mostly on m1 and is relatively insensitive to q2 and q3. We show that eccentricity increase in direct (that is, non-resonant) encounters approximately doubles the rate of BBH inspirals in between resonant encounters. For a given GC mass and radius, the BBH merger rate in metal-rich GCs is approximately double that of metal-poor GCs, because of their (on average) lower BH masses (m1) and steeper BH mass function, yielding binaries with lower q. Conclusions. Our results enable the mass-ratio distribution of dynamically formed BBH mergers to be translated to the underlying BH mass function. The additional mechanism that leads to a doubling of the inspirals provides an explanation for the reported high fraction of in-cluster inspirals in N-body models of clusters.
2025 · Communications in Nonlinear Science and Numerical Simulation
Reinforcement learning for adaptive time-stepping in the chaotic gravitational three-body problem ↗Open accessNumerical Solvers for Ordinary Differential Equations
Abstract
Many problems in astrophysics cover multiple orders of magnitude in spatial and temporal scales. While simulating systems that experience rapid changes in these conditions, it is essential to adapt the (time-) step size to capture the behavior of the system during those rapid changes and use a less accurate time step at other, less demanding, moments. We encounter three problems with traditional methods. Firstly, making such changes requires expert knowledge of the astrophysics as well as of the details of the numerical implementation. Secondly, some parameters that determine the time-step size are fixed throughout the simulation, which means that they do not adapt to the rapidly changing conditions of the problem. Lastly, we would like the choice of time-step size to balance accuracy and computation effort. We address these challenges with Reinforcement Learning by training it to select the time-step size dynamically. We use the integration of a system of three equal-mass bodies that move due to their mutual gravity as an example of its application. With our method, the selected integration parameter adapts to the specific requirements of the problem, both in terms of computation time and accuracy while eliminating the expert knowledge needed to set up these simulations. Our method produces results competitive to existing methods and improve the results found with the most commonly-used values of time-step parameter. This method can be applied to other integrators without further retraining. We show that this extrapolation works for variable time-step integrators but does not perform to the desired accuracy for fixed time-step integrators.
2025 · SSRN Electronic Journal · preprint
Reinforcement Learning for the Determination of the Bridge Time Step in Cluster Dynamics Simulations ↗Free copyNumerical Solvers for Ordinary Differential Equations
2025 · Leiden Repository (Leiden University)
Exploring the role of protostellar jets in simulations of star cluster formation using Torch ↗Free copyFree PDF ↗Astrophysics and Star Formation Studies Abstract
Since most stars form in clusters, studying star formation requires understanding all stages of star cluster formation and evolution, including the initial collapse of molecular gas, the formation of stars and the expulsion of gas from the newly formed cluster, and the late-time evolution and potential disruption of the cluster. A wide range of physical mechanisms shape each of these processes, including a variety of modes of stellar feedback. To study these mechanisms, we use Torch, a numerical framework optimized for simulating the formation and evolution of star clusters. Torch combines the adaptive mesh refinement, magnetohydrodynamical code FLASH with the Astrophysical MUltipurpose Software Environment (AMUSE). In addition, Torch implements a selection of additional physical processes, including several modes of stellar feedback such as radiative feedback, stellar winds, and supernovae. However, Torch did not previously incorporate the effects of protostellar jet feedback, despite the recently demonstrated importance of jets in star formation. We present a new module within Torch that adds protostellar jet feedback and demonstrate its functionality by comparing several simulations with and without protostellar jets. We find that the inclusion of protostellar jets slows star formation in clouds of up to 20,000 solar masses, highlighting the potential of jets to affect the final properties of a star cluster.
2024 · Monthly Notices of the Royal Astronomical Society
Gargantuan chaotic gravitational three-body systems II. Dependence on angular momentum and astrophysical scale ↗Open accessFree PDF ↗Galaxies: Formation, Evolution, Phenomena Abstract
ABSTRACT Recently, we estimated that about 5 per cent of unstable supermassive black hole triple systems are fundamentally unpredictable. These gargantuan chaotic systems are able to exponentially magnify Planck length perturbations to astronomical scales within their dynamical lifetime. These results were obtained in the zero angular momentum limit, which we naively expected to be the most chaotic. Here, we generalize to weakly and non-hierarchical triple systems with a range of non-zero angular momenta by systematically varying the initial virial ratio. We find the surprising result that increasing the angular momentum enhances their ability to amplify small perturbations, which we tracked up to 90 orders of magnitude using the arbitrary-precision N-body code brutus. This result is partially explained by the fact that triples with higher angular momenta have longer lifetimes, allowing for a prolonged exponential growth. However, we also find that for a fixed lifetime, triples with higher angular momenta can amplify perturbations to larger values, indicating that the Lyapunov exponent is also a function of angular momentum. These empirical results provide targets for three-body theories which invoke chaos drivers such as resonance overlap and punctuated chaos. Comparing the zero angular momentum case to our new ensembles with higher angular momenta, we conclude that the percentage of unpredictable supermassive black hole triples increases up to about 30 per cent. A further increase up to about 50 per cent is reached when considering triples on smaller astrophysical scales. Fundamental unpredictability is thus a generic feature of chaotic, self-gravitating triple populations.
2024 · Zenodo (CERN European Organization for Nuclear Research)
Giant bug eats scientific results ↗Free copyScientific Computing and Data Management
Abstract
Computational science, by its nature, involves a wide variety of computer simulations. These are done using software that is usually developed by the researchers themselves, on their own computers or sometimes on large HPC machines. As new methods are developed, new software is written and added to the scientific toolbox. Unfortunately, this software is often poorly written and difficult to reuse. The Astrophysical MUltipurpose Software Environment (AMUSE) comprises more than 50 astrophysical simulation codes created by a variety of researchers, making them available from the Python scripting environment in a well-documented manner. Whil this really helps scientists wishing to run simulations, it does not resolve the above-mentioned issues but merely shifts the responsibility for solving them from the end user to the maintainers of AMUSE. In recent years, AMUSE has suffered from a lack of resources for maintenance, which has caused issues for its users. We have been addressing these issues for AMUSE, but the wider problem of software quality in computational science remains, and deserves more attention.
2024 · Elsevier eBooks · reference-entry
The origin of free-floating objects in the Galaxy ↗Free copyFree PDF ↗Stellar, planetary, and galactic studies 2024 · The Astrophysical Journal
Massive Star Cluster Formation with Binaries. I. Evolution of Binary Populations ↗Open accessAstrophysics and Star Formation Studies
Abstract
Abstract We study the evolution of populations of binary stars within massive cluster-forming regions. We simulate the formation of young massive star clusters within giant molecular clouds with masses ranging from 2 × 104 to 3.2 × 105 M ⊙. We use Torch, which couples stellar dynamics, magnetohydrodynamics, star and binary formation, stellar evolution, and stellar feedback through the Amuse framework. We find that the binary fraction decreases during cluster formation at all molecular cloud masses. The binaries’ orbital properties also change, with stronger and quicker changes in denser, more massive clouds. Most of the changes we see can be attributed to the disruption of binaries wider than 100 au, although the close binary fraction also decreases in the densest cluster-forming region. The binary fraction for O stars remains above 90%, but exchanges and dynamical hardening are ubiquitous, indicating that O stars undergo frequent few-body interactions early during the cluster formation process. Changes to the populations of binaries are a by-product of hierarchical cluster assembly: most changes to the binary population take place when the star formation rate is high, and there are frequent mergers between subclusters in the cluster-forming region. A universal primordial binary distribution based on observed inner companions in the Galactic field is consistent with the binary populations of young clusters with resolved stellar populations, and the scatter between clusters of similar masses could be explained by differences in their formation history.
2024 · The Astrophysical Journal
Binary Disruption and Ejected Stars from Hierarchical Star Cluster Assembly ↗Open accessFree PDF ↗Astrophysics and Star Formation Studies Abstract
Abstract We simulate mergers between star clusters embedded within their natal giant molecular cloud. We extract initial conditions from cloud-scale simulations of cluster formation and introduce different prescriptions for primordial binaries. We find that simulations that do not include primordial binaries result in a larger fraction of unbound stars than simulations that include a prescription for binaries based on observations. We also find a preferred direction of motion for stars that become unbound during the merger. Subcluster mergers within realistic gas environments promote binary disruption, while mergers between idealized, gas-rich spherical clusters do not produce the same disruption. Binary systems with smaller semimajor axes are disrupted in simulations of subcluster mergers within their natal environment compared to simulations that do not include the realistic gas environment. We conclude that binary disruption and the production of an anisotropic distribution of unbound stars are the natural consequences of subcluster mergers during star cluster assembly.
2024 · Journal of Computational Physics
A generalized framework of neural networks for Hamiltonian systems ↗Open accessModel Reduction and Neural Networks
Abstract
When solving Hamiltonian systems using numerical integrators, preserving the symplectic structure is crucial. At the same time, solving chaotic or stiff problems requires integrators to approximate the trajectories with extreme precision. So, integrating Hamilton's equations to a level of scientific reliability such that the answer can be used for scientific interpretation, can be computationally expensive. However, a neural network can be a viable alternative to numerical integrators, offering high-fidelity solutions orders of magnitudes faster.To understand whether it is also important to preserve the symplecticity when neural networks are used, we analyze three well-known neural network architectures that are including the symplectic structure inside the neural network's topology. Between these neural network architectures many similarities can be found. This allows us to formulate a generalized framework for these architectures. In the generalized framework Symplectic Recurrent Neural Networks, SympNets and HénonNets are included as special cases. Additionally, this new framework enables us to find novel neural network topologies by transitioning between the established ones.We compare new Generalized Hamiltonian Neural Networks (GHNNs) against the already established SympNets, HénonNets and physics-unaware multilayer perceptrons. This comparison is performed with data for a pendulum, a double pendulum and a gravitational 3-body problem. In order to achieve a fair comparison, the hyperparameters of the different neural networks are chosen such that the computational costs of all four architectures are the same during inference. A special focus lies on the capability of the neural networks to generalize outside the training data. We found that the GHNNs outperform all other neural network architectures.
2024 · Astronomy and Astrophysics
Evaluating the gravitational wave detectability of globular clusters and the Magellanic Clouds for LISA ↗Open accessFree PDF ↗Pulsars and Gravitational Waves Research Abstract
We used the stellar evolution code BPASS and the gravitational wave (GW) simulation code LEGWORK to simulate populations of compact binaries that may be detected by the future space-based GW detector LISA. Specifically, we simulate the Magellanic Clouds and binary populations mimicking several globular clusters, neglecting dynamical effects. We find that a handful of sources should be detectable in each of the Magellanic Clouds, but for globular clusters the amount of detectable sources will likely be less than one each. We compared our results to earlier research and find that our predicted numbers are several dozen times lower than both the results from calculations that used the stellar evolution code BSE and take dynamical effects into account, and results from calculations that used the stellar evolution code SEBA for the Magellanic Clouds. Earlier research that compared BPASS models for GW sources in the Galactic disk with BSE models found a similarly sized discrepancy. We determine that this discrepancy is caused by differences between the stellar evolution codes, particularly in the treatment of mass transfer and common-envelope events in binaries: in BPASS mass transfer is more likely to be stable and tends to lead to less orbital shrinkage in the common-envelope phase than in other codes. This difference results in fewer compact binaries with periods short enough to be detected by LISA existing in the BPASS population. For globular clusters, we conclude that the impact of dynamical effects is uncertain based on the literature, but the differences in stellar evolution have an effect of a factor of 20 to 40 on the number of detectable binaries.
2024 · Astronomy and Astrophysics
Origin of transition disk cavities ↗Open accessAstrophysics and Star Formation Studies
Abstract
Context. Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Aims. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk. Methods. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos’ orbits. We vary the planet and disk properties to understand the resulting dust profile. Results. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is 10−2 − 10−4. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates. Conclusions. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.
2024 · Nature
Two waves of massive stars running away from the young cluster R136 ↗Free copyFree PDF ↗Stellar, planetary, and galactic studies 2024 · Nature Astronomy
Trajectory of the stellar flyby that shaped the outer Solar System ↗Abstract
Abstract Unlike the Solar System planets, thousands of smaller bodies beyond Neptune orbit the Sun on eccentric (e > 0.1 and i > 3°) orbits. While migration of the giant planets during the early stages of Solar System evolution could have induced substantial scattering of trans-Neptunian objects (TNOs), this process cannot account for the small number of distant TNOs (rp > 60 au) outside the planets’ reach. The alternative scenario of the close flyby of another star can instead produce all these TNO features simultaneously, but the possible parameter space for such an encounter is vast. Here we compare observed TNO properties with thousands of flyby simulations to determine the specific properties of a flyby that reproduces all the different dynamical TNO populations, their locations and their relative abundances, and find that a $$0.{8}_{-0.1}^{+0.1}\,{M}_{\odot }$$ 0 . 8 − 0.1 + 0.1 M ⊙ star passing at a distance of rp = 110 ± 10 au, inclined by i = 70° $${\,}_{-10}^{+5}$$ + 5 − 10 , gives a near-perfect match. This flyby also replicates the retrograde TNO population, which has proved difficult to explain. Such a flyby is reasonably frequent; at least 140 million solar-type stars in the Milky Way are likely to have experienced a similar one. In light of these results, we predict that the upcoming Vera Rubin telescope will reveal that distant and retrograde TNOs are relatively common.
2024 · Astronomy and Astrophysics
VENICE: A multi-scale operator-splitting algorithm for multi-physics simulations ↗Open accessStellar, planetary, and galactic studies
Abstract
Context. We present VENICE, an operator-splitting algorithm to integrate a numerical model on a hierarchy of timescales. Aims. VENICE allows a wide variety of different physical processes operating on different scales to be coupled on individual and adaptive time-steps. It therewith mediates the development of complex multi-scale and multi-physics simulation environments with a wide variety of independent components. Methods. The coupling between various physical models and scales is dynamic, and realised through (Strang) operators splitting using adaptive time-steps. Results. We demonstrate the functionality and performance of this algorithm using astrophysical models of a stellar cluster, first coupling gravitational dynamics and stellar evolution, then coupling internal gravitational dynamics with dynamics within a galactic background potential, and finally combining these models while also introducing dwarf galaxy-like perturbers. These tests show numerical convergence for decreasing coupling timescales, demonstrate how VENICE can improve the performance of a simulation by shortening coupling timescales when appropriate, and provide a case study of how VENICE can be used to gradually build up and tune a complex multi-physics model. Although the examples provided here couple dedicated numerical models, VENICE can also be used to efficiently solve systems of stiff differential equations.
2024 · Astronomy and Astrophysics
Massive star cluster formation ↗Open accessAstrophysics and Star Formation Studies
Abstract
Two main mechanisms have classically been proposed for the formation of runaway stars. In the binary supernova scenario (BSS), a massive star in a binary explodes as a supernova, ejecting its companion. In the dynamical ejection scenario, a star is ejected during a strong dynamical encounter between multiple stars. We propose a third mechanism for the formation of runaway stars: the subcluster ejection scenario (SCES), where a subset of stars from an infalling subcluster is ejected out of the cluster via a tidal interaction with the contracting gravitational potential of the assembling cluster. We demonstrate the SCES in a star-by-star simulation of the formation of a young massive cluster from a 106 M⊙ gas cloud using the TORCH framework. This star cluster forms hierarchically through a sequence of subcluster mergers determined by the initial turbulent, spherical conditions of the gas. We find that these mergers drive the formation of runaway stars in our model. Late-forming subclusters fall into the central potential, where they are tidally disrupted, forming tidal tails of runaway stars that are distributed highly anisotropically. Runaways formed in the same SCES have similar ages, velocities, and ejection directions. Surveying observations, we identify several SCES candidate groups with anisotropic ejection directions. The SCES is capable of producing runaway binaries: two wide dynamical binaries in infalling subclusters were tightened through ejection. This allows for another velocity kick via subsequent via a subsequent BSS ejection. An SCES-BSS ejection is a possible avenue for the creation of hypervelocity stars unbound to the Galaxy. The SCES occurs when subcluster formation is resolved. We expect nonspherical initial gas distributions to increase the number of calculated runaway stars, bringing it closer to observed values. The observation of groups of runaway stars formed via the SCES can thus reveal the assembly history of their natal clusters.
2024 · Astronomy and Astrophysics
Suppression of giant planet formation around low-mass stars in clustered environments ↗Open accessFree PDF ↗Astrophysics and Star Formation Studies Abstract
Context. Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. However, the effects of this environment on the planet formation process are important, especially in the earliest stage. Aims. We investigate the differences in planet populations forming in star-cluster environments through pebble accretion and compare these results with planet formation around isolated stars. We strive to provide potential signatures of the young planetary systems to guide future observations. Methods. We present a new planet population synthesis code designed for clustered environments. This planet formation model is based on pebble accretion and includes migration in the circumstellar disk. The disk’s gas and dust have been evolved via 1D simulations, while considering the effects of photo-evaporation of the nearby stars. Results. Planetary systems in a clustered environment are different than those born in isolation; the environmental effects are important for a wide range of observable parameters and the eventual architecture of the planetary systems. Planetary systems born in a clustered environment lack cold Jupiters, as compared to isolated planetary systems. This effect is more pronounced for low-mass stars (≲0.2 M⊙). On the other hand, planetary systems born in clusters show an excess of cold Neptune around these low-mass stars. Conclusions. In future observations, finding an excess of cold Neptunes and a lack of cold Jupiters could be used to constrain the birth environments of these planetary systems. Exploring the dependence of cold Jupiter’s intrinsic occurrence rate on stellar mass offers insights into the birth environment of their proto-embryos.
2024 · Astronomy and Astrophysics
Isles of regularity in a sea of chaos amid the gravitational three-body problem ↗Open accessPulsars and Gravitational Waves Research
Abstract
Context. The three-body problem (3BP) poses a longstanding challenge in physics and celestial mechanics. Despite the impossibility of obtaining general analytical solutions, statistical theories have been developed based on the ergodic principle. This assumption is justified by chaos, which is expected to fully mix the accessible phase space of the 3BP. Aims. This study probes the presence of regular (i.e. non-chaotic) trajectories within the 3BP and assesses their impact on statistical escape theories. Methods. Using three-body simulations performed with the accurate, regularized code TSUNAMI, we established criteria for identifying regular trajectories and analysed their impact on statistical outcomes. Results. Our analysis reveals that regular trajectories occupy a significant fraction of the phase space, ranging from 28% to 84% depending on the initial setup, and their outcomes defy the predictions of statistical escape theories. The coexistence of regular and chaotic regions at all scales is characterized by a multi-fractal behaviour. Integration errors manifest as numerical chaos, artificially enhancing the mixing of the phase space and affecting the reliability of individual simulations, yet preserving the statistical correctness of an ensemble of realizations. Conclusions. Our findings underscore the challenges in applying statistical escape theories to astrophysical problems, as they may bias results by excluding the outcome of regular trajectories. This is particularly important in the context of formation scenarios of gravitational wave mergers, where biased estimates of binary eccentricity can significantly impact estimates of coalescence efficiency and detectable eccentricity.
2024 · SciPost Astronomy
The origin and evolution of wide Jupiter mass binary objects in young stellar clusters ↗Open accessFree PDF ↗Stellar, planetary, and galactic studies Abstract
The recently observed population of 540 free-floating Jupiter-mass objects, including 40 dynamically soft pairs, and two triples, in the Trapezium cluster have raised interesting questions on their formation and evolution. We test various scenarios for the origin and survivability of these free floating Jupiter-mass objects and Jupiter-mass Binary Objects (JuMBOs) in the Trapezium cluster. The numerical calculations are performed by direct N N -body integration of the stars and planets in the Trapezium cluster starting with a wide variety of planets in various configurations. We discuss four models: \mathcal{SPP} 𝒮 𝒫 𝒫 , in which selected stars have two outer orbiting Jupiter-mass planets; \mathcal{SPM} 𝒮 𝒫 ℳ , where selected stars are orbited by Jupiter-mass planet-moon pairs; \mathcal{ISF} ℐ 𝒮 ℱ in which JuMBOs form in situ with the stars, and \mathcal{FFC} ℱ ℱ 𝒞 , where we introduce a population of free-floating single Jupiter-mass objects, but no initialised binaries. Models \mathcal{FFC} ℱ ℱ 𝒞 and \mathcal{SPP} 𝒮 𝒫 𝒫 fail to produce enough JuMBOs. Models \mathcal{SPM} 𝒮 𝒫 ℳ can produce sufficient free-floaters and JuMBOs, but requires unusually wide orbits for the planet-moon system around the star. The observed JuMBOs and free-floating Jupiter-mass objects in the Trapezium cluster are best reproduced if they formed in pairs and as free-floaters together with the other stars in a smooth (Plummer) density profile with a virial radius of \sim 0.5 ∼ 0.5 pc. A fractal (with fractal dimension 1.6) stellar density distribution also works, but requires relatively recent formations ( ⪆ 0.2 ⪆ 0.2 Myr after the other stars formed) or a high ( ⪆ 50 ⪆ 50 %) initial binary fraction. This would make the primordial binary fraction of JuMBOs even higher than the already large observation fraction of \sim 8 ∼ 8 % (42/540). The fraction of JuMBOs will continue to drop with time, and the lack of JuMBOs in Upper Scorpius could then result in its higher age, causing more JuMBOs to be ionized. We then also predict that the interstellar density of Jupiter-mass objects (mostly singles with some \sim 2 ∼ 2 % lucky surviving binaries) is \sim 0.05 ∼ 0.05
2024 · Research Square · preprint
Once upon a time in the Oort cloud; when did the Sun Lost its Siblings ↗Free copyAstro and Planetary Science
Abstract
Abstract The Sun was born together with a few thousand other stars in a clustered environment. So long as it was a cluster member, no asteroid ejected by the giant planets could remain bound to the Sun, preventing the formation of an Oort cloud. The number of asteroids in the Oort cloud and their combined mass can then be used to time the moment the Sun left the nest. If the Sun left within the first 5 Myr, the Oort cloud would have been up to 4 times more massive than today’s best estimate. The Oort cloud would be considerably less massive than today’s best estimate if the Sun left later than 17 Myr. The orbital distribution of the inner Oort cloud (between ∼ 100 and ∼ 104 au) and the detached Kuiper-belt populations are even more sensitive to the moment the Sun lost its siblings. The morphology of the low-eccentricity inner-Oort cloud are most sensitive to the Sun’s escape time and can further constrain the parent-cluster parameters.
2024 · Zenodo (CERN European Organization for Nuclear Research) · dataset
Flow map data of the singel pendulum, double pendulum and 3-body problem ↗Free copyModel Reduction and Neural Networks
Abstract
This dataset was constructed to compare the performance of various neural network architectures learning the flow maps of Hamiltonian systems. It was created for the paper: A Generalized Framework of Neural Networks for Hamiltonian Systems. The dataset consists of trajectory data from three different Hamiltonian systems. Namely, the single pendulum, double pendulum and 3-body problem. The data was generated using numerical integrators. For the single pendulum, the symplectic Euler method with a step size of 0.01 was used. The data of the double pendulum was also computed by the symplectic Euler method, however, with an adaptive step size. The trajectories of the 3-body problem were calculated by the arbitrarily high-precision code Brutus. For each Hamiltonian system, there is one file containing the entire trajectory information (*_all_runs.h5.1). In these files, the states along all trajectories are recorded with a step size of 0.01. These files are composed of several Pandas DataFrames. One DataFrame per trajectory, called "run0", "run1", ... and finally one large DataFrame in which all the trajectories are combined, called "all_runs". Additionally, one Pandas Series called "constants" is contained in these files, in which several parameters of the data are listed. Also, there is a second file per Hamiltonian system in which the data is prepared as features and labels ready for neural networks to be trained (*_training.h5.1). Similar to the first type of files, they contain a Series called "constants". The features and labels are then separated into 6 DataFrames called "features", "labels", "val_features", "val_labels", "test_features" and "test_labels". The data is split into 80% training data, 10% validation data and 10% test data. The code used to train various neural network architectures on this data can be found on GitHub at: https://github.com/AELITTEN/GHNN. Already trained neural networks can be found on GitHub at: https://github.com/AELITTEN/NeuralNets_GHNN. Single pendulum Double pendulum 3-body problem Number of trajectories 500 2000 5000 final time in all_runs T (one period of the pendulum) 10 10 final time in training data 0.25*T 5 5 step size in training data 0.1 0.1 0.5
2024 · dataset
Supplemental data for the paper "Massive Star Cluster Formation I. High Star Formation Efficiency While Resolving Feedback of Individual Stars" ↗Astrophysics and Star Formation Studies
Abstract
This repository contains supporting data for the paper "“Massive Star Cluster Formation I. High Star Formation Efficiency While Resolving Feedback of Individual Stars.” Polak et al. 2024, Astron. Astrophys., 690, A94.
2024 · Monthly Notices of the Royal Astronomical Society
Magnetospheric flows in X-ray pulsars – I. Instability at super-Eddington regime of accretion ↗Open accessFree PDF ↗Astrophysical Phenomena and Observations Abstract
ABSTRACT Within the magnetospheric radius, the geometry of accretion flow in X-ray pulsars is shaped by a strong magnetic field of a neutron star. Starting at the magnetospheric radius, accretion flow follows field lines and reaches the stellar surface in small regions located close to the magnetic poles of a star. At low mass accretion rates, the dynamics of the flow is determined by gravitational attraction and rotation of the magnetosphere due to the centrifugal force. At the luminosity range close to the Eddington limit and above it, the flow is additionally affected by the radiative force. We construct a model simulating accretion flow dynamics over the magnetosphere, assuming that the flow strictly follows field lines and is affected by gravity, radiative, and centrifugal forces only. The magnetic field of a neutron star is taken to be dominated by the dipole component of arbitrary inclination with respect to the accretion disc plane. We show that accretion flow becomes unstable at high mass accretion rates and tends to fluctuate quasi-periodically with a typical period comparable to the free-fall time from the inner disc radius. The inclination of a magnetic dipole with respect to the disc plane and strong anisotropy of X-ray radiation stabilize the mass accretion rate at the poles of a star, but the surface density of material covering the magnetosphere fluctuates even in this case.
2024 · Astronomy and Astrophysics
The steady state of intermediate-mass black holes near a supermassive black hole ↗Open accessFree PDF ↗Astrophysical Phenomena and Observations Abstract
Aims. Our aim is to investigate the properties of a cluster of intermediate-mass black holes (IMBHs) surrounding a supermassive black hole (SMBH). Methods. We simulated clusters of equal-mass IMBHs (mIMBH = 103 M⊙) initialised in a shell between 0.15 ≤ r [pc] ≤ 0.25 centred about a SMBH. We explored the influence of the cluster population and SMBH on the merger rate, the ejection rate, and the escape velocity. For MSMBH = 4 × 106 M⊙, we used both a Newtonian and post-Newtonian formalism, going up to the 2.5th order and including cross terms. We ran 40 and 60 simulations per cluster population for either formalism, respectively. For the other two SMBH masses (MSMBH = 4 × 105 M⊙ and MSMBH = 4 × 107 M⊙), we modelled the system only taking into account relativistic effects. In the case of MSMBH = 4 × 105 M⊙, 30 simulations were run per population. For MSMBH = 4 × 107 M⊙ we ran ten simulations per population. The simulations ended once a black hole escaped the cluster, a merger occured, or the system evolved until 100 Myr. Results. The post-Newtonian formalism accelerates the loss rate of IMBHs compared to the Newtonian formalism. Ejections occur more often for lighter SMBHs while more massive ones increase the rate of mergers. Although relativistic effects allow for circularisation, all merging binaries have e ≳ 0.97 when measured 1 − 2 kyr before the merging event. The strongest gravitational wave signals are often sourced by IMBH-SMBH binaries that eventually merge. Strong signals were suppressed during our Newtonian calculations since, here, the IMBH typically stalls in the vicinity of the SMBH, before being generally ejected via the slingshot mechanism or experiencing a head-on collision. Weaker and more frequent signals are expected from gravitational wave radiation emitted in a flyby. In our post-Newtonian calculations, 30/406 (7.4%) of the gravitational wave events capable of being observed with LISA and μAres were detected as gravitational wave capture binaries with the remaining being in-cluster mergers. Throughout our investigation, no IMBH-IMBH binaries were detected.
2024 · Astronomy and Astrophysics
Individual chaotic behaviour of the S-stars in the Galactic centre ↗Open accessStellar, planetary, and galactic studies
Abstract
Located at the core of the Galactic centre, the S-star cluster serves as a remarkable illustration of chaos in dynamical systems. The long-term chaotic behaviour of this system can be studied with gravitational N-body simulations. By applying a small perturbation to the initial position of star S5, we can compare the evolution of this system to its unperturbed evolution. This results in two solutions that diverge exponentially, defined by the separation in position space δr, with an average Lyapunov timescale of ∼420 yr, corresponding to the largest positive Lyapunov exponent. Even though the general trend of the chaotic evolution is governed in part by the supermassive black hole Sagittarius A∗ (Sgr A∗), individual differences between the stars can be noted in the behaviour of their phase-space curves. We present an analysis of the individual behaviour of the stars in this Newtonian chaotic dynamical system. The individuality of their behaviour is evident from offsets in the position space separation curves of the S-stars and the black hole. We propose that the offsets originate from the initial orbital elements of the S-stars, where Sgr A∗ is considered in one of the focal points of the Keplerian orbits. Methods were considered to find a relation between these elements and the separation in position space. Symbolic regression provides the clearest diagnostics for finding an interpretable expression for the problem. Our symbolic regression model indicates that ⟨δr⟩ ∝ e2.3, implying that the time-averaged individual separation in position space increases rapidly with the initial eccentricity of the S-stars.
2024 · Figshare · other
The Ecological Impact of High-performance Computing in Astrophysics ↗Free copyGreen IT and Sustainability
Abstract
This repository contains the python scripts and data for generating the 3 figure panels for the manuscript: The Ecological Impact of High-performance Computing in Astrophysics.Computer use in astronomy continues to increase, and so also its impact on the environment. To minimize the effects, astronomers should avoid interpreted scripting languages such as Python, and favor the optimal use of energy-efficient workstations.
2024 · Leiden Repository (Leiden University)
Cold planet population formed in star-clustered environment ↗Astrophysics and Star Formation Studies
Abstract
Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. The effect of this environment on the planet-formation process, however, is profound, especially in the earliest stage. We investigate the differences in planet populations forming in star cluster environments through pebble accretion and compare these results with formation around isolated stars. We provide potential signatures induced upon the young planetary systems to guide future observation. We design and present a new planet population synthesizes code for cluster environments. Our planet formation model is based on pebble accretion and includes migration in the protoplanet disk. The disk's gas and dust components are evolved using 1D hydrodynamical simulations while considering the effects of photo-evaporation of the nearby stars and close encounters in the clustered environment. Planetary systems in a clustered environment are profoundly different than those born in isolation; the environmental effects are important for a wide range of observable parameters and for the eventual architecture of the planetary systems. Planetary systems born in a clustered environment show a considerable lack in the occurrence rate of cold Jupiters compared to isolated planetary systems. This effect is most pronounced for low-mass stars (<0.2 $M_\odot$). On the other hand, planetary systems born in clusters show an excess of cold Neptune around these low-mass stars. Finding such an excess of cold Neptunes, or a lack of cold Jupiters, in future observations, could be used to constrain the birth environments of these planetary systems. Exploring the dependence of cold Jupiter's intrinsic occurrence rate on stellar mass provides insights into the planet-formation process in conjunction with the influence of the birth environment.
2024 · Leiden Repository (Leiden University) · conference-abstract
The tidal streams of interstellar objects ↗Free copyFree PDF ↗Stellar, planetary, and galactic studies Abstract
We study the dynamics of interstellar objects (ISOs), which provide samples of the planetesimal formation process taking place across the Galaxy and throughout Galactic history. Once ISOs escape their system of origin, they orbit the Galaxy in leading and trailing tidal streams around their progenitors. We characterize the properties of these streams for a range of progenitors and ejection mechanisms. We find that streams are primarily distinguished by the typical velocity at which the ISOs are ejected from their progenitors, that streams can often wrap around the Galaxy, and that the velocity and density structure of the streams can have a large effect on the rate at which we should expect to observe ISOs in upcoming Solar System surveys.
2023 · Zenodo (CERN European Organization for Nuclear Research) · dataset
Who shot Melnick 34: the last bully binary ejected from the young star cluster R136 in the Tarantula nebula ↗Free copyStellar, planetary, and galactic studies
Abstract
# Melnick 34 # readme.md # this file: # directory structure: -raw_data # Raw data files -figures # Auxilary figures (pdf) files -scr # Runscript for performing simulations and analysing data -src # Python scripts for performing runs -generic_runs (20) # generaic runs -a4Axxa6v7 # runs for g=4, h=[30, 320]au, i=6au orbital separations -a4A50a6v7 # specific runs for g=4, h=50, i=6au orbital separations -Model_B # Model B runs with range of relative encounter velocity -Model_G # Model B runs with range of relative encounter velocity -var_velocity (8) # Series of shorter runs probing relative velocity Total number of simulations -generic_runs: 20 runs of 4000 encounters -a4Axxa6v7 19 runs of 4000 encounters -a4A50a6v7 14 runs of 400 encounters -Model_B 9 runs of 4000 encounters -Model_G 3 runs of 4000 encounters -var_velocity 8 runs of 4000 encounters Approximate number of runs: 212800 File structure for the simulations (85 simulation output files) raw_data/Model_B contains the following files: S.M130.0.m130.0_m50.0.M130.0.m80.0.A10.0_a100.0.a10.0.v7.0.out ...etc. The strucutre of these files is as follows S.M130.0.m130.0_m50.0.M130.0.m80.0.A10.0_a100.0.a10.0.v7.0.out a.bbbbbb.cccccc_ddddd.eeeeee.fffff.ggggg_hhhhhh_iiiii.jjjj.out a: run performed with Scatter "S" b: mass of the primary of the target inner binary (t1) c: mass of the decondary of the target outer binary's primary (t21) d: mass of the tertiary star of the outer binary's secondary (t22) e: mass of the primary incoming (projectile) binary (p1) f: mass of the secondary incoming (projectile) binary (p2) g: semi-major axis of the inner target binary h: semi-major axis of the outer target binary i: semi-major axis of the incoming projectile binary j: relative velocity at infinity of the encounter between triple and binary Masses are in MSun velocities are in km/s semi-major axes are in au How to perform the simulations. The directory scr contains a series of csh scripts used to perform the simulations. The simulations themselves require starlab (https://github.com/amusecode/Starlab) The directory scr contains the following files: run_scatter.csh # Run a single smake scatter to tune initial conditions RunScatter.csh # run script for performing a multi-body experiment run_all_a10A100a10v7kms.csh # simple script to run series of simulations run_all_a5A50a5v7kms.csh # simple script to run series of simulations run_sigma5.csh # run mutiple sigma experiments using the python driver run_all.csh # run a series
2023 · Zenodo (CERN European Organization for Nuclear Research) · dataset
JuMBOs: Jupiter-Mass Binary Objects as originating from four models ISF, FFC, SPP and SPP ↗Free copyStellar, planetary, and galactic studies
Abstract
# JuMBOs # README.md # this file: # directory structure: - data # place holder for the data files - Observations # Observational data - raw # raw simulations data - FFC # data for model Free-Floating-Capture - std # standard data runs (see table 1) - others # Auxilary runs to support various arguments in the manuscript - ISF # data for model In-Situ-Formation - std # standard data runs (see table 1) - others # Auxilary runs to support various arguments in the manuscript - SPM # data for model Star-Planet-Moon - SPP # data for model Star-Planet-Planet - scr # repository of shell scripts to automate data processing - plot # some ploting routines - src # project's source files for generating initial conditions and running - rdc # data reduction routines - run # runscripts and initial conditions generator File structure for model FFC: The standard filename is composed of the following elements FrN2500n600x1.2ffc_R0.25pcQ05_R1 aabbbbbccccddddeee_fffffffqqq_hh a: initial cluster density profile model designation (Pl for Plummer, Fr for fractal) b: Number of stars in the simulation (generally 2500) c: Number of jumbos (or free floaters as in model FFC) in the initial snapshot (usually 300) d: Power-law slope of the initial jumbo mass funciton (usually -1.2, but also runs with 0.0) e: model name indicating the nature of the initial jumbos/JMOs (fcc, isf, spp, or spm) f: Initial cluster virial radius in parsec (usually 0.25pc, 0.50pc or 1.0pc) g: Initial cluster's virial radio (usually Q=0.5, indicating virialized). h: Integrer number for the run, some runs are repeated with a different random seed. Two of the models are run with a wider range of initial conditions. The standard runs are then stored in the sub-directory "std", and the other runs in "others". For example, run FCC/others/FrN2500n10000x1.5m0.01ffc_R1.0pcQ05_R1 contains results from a simulation with 10000 JMOs with a power-law mass function with a slope of -1.5 (rather than -1.2 for most runs) Each directory "std" for te various model names contain sub directories for each model These subdirectories are named: FrN2500ccccddddeee_R0.25pcqqq_R1 FrN2500ccccddddeee_R0.5pcqqq_R1 FrN2500ccccddddeee_R1.0pcqqq_R1 PlN2500ccccddddeee_R0.25pcqqq_R1 PlN2500ccccddddeee_R0.5pcqqq_R1 PlN2500ccccddddeee_R1.0pcqqq_R1 One directory for each of the Fractal and Plummer models. Each of these directories contains the following files: out.data # the raw simulation output file (ASCII) jumbos_i0000.amuse # initial conditions
2023 · Journal of Computational Physics
A hybrid approach for solving the gravitational N-body problem with Artificial Neural Networks ↗Open accessModel Reduction and Neural Networks
Abstract
Simulating the evolution of the gravitational N-body problem becomes extremely computationally expensive as N increases since the problem complexity scales quadratically with the number of bodies. In order to alleviate this problem, we study the use of Artificial Neural Networks (ANNs) to replace expensive parts of the integration of planetary systems. Neural networks that include physical knowledge have rapidly grown in popularity in the last few years, although few attempts have been made to use them to speed up the simulation of the motion of celestial bodies. For this purpose, we study the advantages and limitations of using Hamiltonian Neural Networks to replace computationally expensive parts of the numerical simulation of planetary systems. We compare the results of the numerical integration of a planetary system with asteroids with those obtained by a Hamiltonian Neural Network and a conventional Deep Neural Network. Due to the non-linear nature of the gravitational equations of motion, errors in the integration propagate, which may lead to divergence from the reference solution. To increase the robustness of a method that uses neural networks, we propose a hybrid integrator that evaluates the prediction of the network and replaces it with the numerical solution if considered inaccurate.Hamiltonian Neural Networks can make predictions that resemble the behavior of symplectic integrators but are challenging to train and in our case fail when the inputs differ ∼7 orders of magnitude. In contrast, Deep Neural Networks are easy to train but fail to conserve energy, leading to fast divergence from the reference solution. The hybrid integrator designed to include the neural networks increases the reliability of the method and prevents large energy errors without increasing the computing cost significantly. For the problem at hand, the use of neural networks results in faster simulations when the number of asteroids is ≥70.
2023 · Monthly Notices of the Royal Astronomical Society
Punctuated chaos and the unpredictability of the Galactic Centre S-star orbital evolution ↗Open accessFree PDF ↗Stellar, planetary, and galactic studies Abstract
ABSTRACT We investigate the chaotic behaviour of the S-star cluster in the Galactic Centre using precise N-body calculations, free from round-off or discretization errors. Our findings reveal that chaos among the Galactic Centre S-stars arises from close encounters, particularly among pairs and near the massive central body. These encounters induce perturbations, causing sudden changes in the orbital energies of the interacting stars. Consequently, neighbouring solutions experience roughly exponential growth in separation. We propose a theory of ‘punctuated chaos’ that describes the S-star cluster’s chaotic behaviour. This phenomenon results from nearly linear growth in the separation between neighbouring orbits after repeated finite perturbations. Each participating star’s orbit experiences discrete, abrupt changes in energy due to the perturbations. The cumulative effect of these events is further amplified by the steady drift in orbital phase. In the Galactic Centre, perturbations originate from coincidental encounters occurring within a distance of ≲100 au between at least two stars (in some cases, three stars). Our model satisfactorily explains the observed exponential growth in the 27 S-stars cluster. We determine that the S-star system has a Lyapunov time-scale of approximately 462 ± 74 yr. For the coming millennium, chaos in the S-star cluster will be driven mainly by a few of the closest orbiting stars: S2, S5, S6, S8, S9, S14, S18, S31, S21, S24, S27, S29, and S38.
2023 · Living Reviews in Relativity
Cosmology with the Laser Interferometer Space Antenna ↗Open accessPulsars and Gravitational Waves Research
Abstract
Abstract The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe.
2023 · The Astrophysical Journal
Modeling the Chemical Enrichment History of the Bulge Fossil Fragment Terzan 5 ↗Open accessStellar, planetary, and galactic studies
Abstract
Abstract Terzan 5 is a heavily obscured stellar system located in the inner Galaxy. It has been postulated to be a stellar relic, a bulge fossil fragment witnessing the complex history of the assembly of the Milky Way bulge. In this paper, we follow the chemical enrichment of a set of putative progenitors of Terzan 5 to assess whether the chemical properties of this cluster fit within a formation scenario in which it is the remnant of a primordial building block of the bulge. We can explain the metallicity distribution function and the runs of different element-to-iron abundance ratios as functions of [Fe/H] derived from optical-infrared spectroscopy of giant stars in Terzan 5 by assuming that the cluster experienced two major star formation bursts separated by a long quiescent phase. We further predict that the most metal-rich stars in Terzan 5 are moderately He-enhanced, and we predict a large spread of He abundances in the cluster, Y ≃ 0.26–0.335. We conclude that current observations fit within a formation scenario in which Terzan 5 originated from a pristine or slightly metal-enriched gas clump about one order of magnitude more massive than its present-day mass. Losses of gas and stars played a major role in shaping Terzan 5 the way we see it now. The iron content of the youngest stellar population is better explained if the white dwarfs that give rise to type Ia supernovae (the main Fe factories) sink toward the cluster center, rather than being stripped by the strong tidal forces exerted by the Milky Way in the outer regions.
2023 · International Journal of Modern Physics D
Punctuated chaos and indeterminism in self-gravitating many-body systems ↗Free copyFree PDF ↗Mathematical Dynamics and Fractals Abstract
Dynamical chaos is a fundamental manifestation of gravity in astrophysical, many-body systems. The spectrum of Lyapunov exponents quantifies the associated exponential response to small perturbations. Analytical derivations of these exponents are critical for understanding the stability and predictability of observed systems. This paper presents a new model for chaos in systems with eccentric and crossing orbits. Here, exponential divergence is not a continuous process but rather the cumulative effect of an ever-increasing linear response driven by discrete events at regular intervals, i.e. punctuated chaos. We show that long-lived systems with punctuated chaos can magnify Planck length perturbations to astronomical scales within their lifetime, rendering them fundamentally indeterministic.
2023 · Living Reviews in Relativity
Astrophysics with the Laser Interferometer Space Antenna ↗Open accessFree PDF ↗Pulsars and Gravitational Waves Research Abstract
Abstract The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.
2023 · Monthly Notices of the Royal Astronomical Society
Early evolution and three-dimensional structure of embedded star clusters ↗Free copyFree PDF ↗Astrophysics and Star Formation Studies Abstract
ABSTRACT We perform simulations of star cluster formation to investigate the morphological evolution of embedded star clusters in the earliest stages of their evolution. We conduct our simulations with Torch, which uses the Amuse framework to couple state-of-the-art stellar dynamics to star formation, radiation, stellar winds, and hydrodynamics in Flash. We simulate a suite of 104 M⊙ clouds at 0.0683 pc resolution for ∼2 Myr after the onset of star formation, with virial parameters α = 0.8, 2.0, 4.0 and different random samplings of the stellar initial mass function and prescriptions for primordial binaries. Our simulations result in a population of embedded clusters with realistic morphologies (sizes, densities, and ellipticities) that reproduce the known trend of clouds with higher initial α having lower star formation efficiencies. Our key results are as follows: (1) Cluster mass growth is not monotonic, and clusters can lose up to half of their mass while they are embedded. (2) Cluster morphology is not correlated with cluster mass and changes over ∼0.01 Myr time-scales. (3) The morphology of an embedded cluster is not indicative of its long-term evolution but only of its recent history: radius and ellipticity increase sharply when a cluster accretes stars. (4) The dynamical evolution of very young embedded clusters with masses ≲1000 M⊙ is dominated by the overall gravitational potential of the star-forming region rather than by internal dynamical processes such as two- or few-body relaxation.
2023 · Monthly Notices of the Royal Astronomical Society
Radiation shielding of protoplanetary discs in young star-forming regions ↗Free to readFree PDF ↗Astrophysics and Star Formation Studies Abstract
ABSTRACT Protoplanetary discs spend their lives in the dense environment of a star-forming region. While there, they can be affected by nearby stars through external photoevaporation and dynamic truncations. We present simulations that use the amuse framework to couple the torch model for star cluster formation from a molecular cloud with a model for the evolution of protoplanetary discs under these two environmental processes. We compare simulations with and without extinction of photoevaporation-driving radiation. We find that the majority of discs in our simulations are considerably shielded from photoevaporation-driving radiation for at least 0.5 Myr after the formation of the first massive stars. Radiation shielding increases disc lifetimes by an order of magnitude and can let a disc retain more solid material for planet formation. The reduction in external photoevaporation leaves discs larger and more easily dynamically truncated, although external photoevaporation remains the dominant mass-loss process. Finally, we find that the correlation between disc mass and projected distance to the most massive nearby star (often interpreted as a sign of external photoevaporation) can be erased by the presence of less massive stars that dominate their local radiation field. Overall, we find that the presence and dynamics of gas in embedded clusters with massive stars is important for the evolution of protoplanetary discs.
2023 · The Astrophysical Journal
Early-forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly ↗Open accessFree PDF ↗Astrophysics and Star Formation Studies Abstract
Abstract Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suite Torch, combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer, N-body dynamics, and stellar feedback, to model four initially identical 104 M ⊙ giant molecular clouds with a Gaussian density profile peaking at 521.5 cm−3. Using the Torch software suite through the AMUSE framework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100 M ⊙). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildup of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster.
2023 · AIP conference proceedings · conference-paper
The paradox of infinitesimal granularity: Chaos and the reversibility of time in Newton’s theory of gravity ↗Free copyFree PDF ↗Quantum chaos and dynamical systems Abstract
The fundamental laws of physics are time-symmetric, but our macroscopic experience contradicts this. The time reversibility paradox is partly a consequence of the unpredictability of Newton's equations of motion. We measure the dependence of the fraction of irreversible, gravitational N-body systems on numerical precision and find that it scales as a power law. The stochastic wave packet reduction postulate then introduces fundamental uncertainties in the Cartesian phase space coordinates that propagate through classical three-body dynamics to macroscopic scales within the triple's lifetime. The spontaneous collapse of the wave function then drives the global chaotic behavior of the Universe through the superposition of triple systems (and probably multi-body systems). The paradox of infinitesimal granularity then arises from the superposition principle, which states that any multi-body system is composed of an ensemble of three-body problems.
2023 · Figshare · dataset
Punctuated chaos and the unpredictability of the Galactic center S-star orbital evolution ↗Free copyStellar, planetary, and galactic studies
Abstract
#Description of the data. Raw and processed data for the manuscript "Punctuated chaos and the unpredictability of the Galactic center S-star orbital evolution" by Simon Portegies Zwart, Tjarda Boekholt, and Douglas Heggie. The initial conditions for the S-stars are taken from the observed 27 stars by 2009ApJ...692.1075G. We adopted those observed initial conditions and converted them into orbital elements adopting a distance to the black hole of 8178pc and a mass of 4.154e+6 Solar masses. we adopted a current time of 1 January 2021. We subsequently calculate the orbital evolution of all particles (S-stars and black hole) for 10000years. Since the system is chaotic, we adopted Brutus (see 2018CNSNS..61..160P) with a tolerance of $10^{-24}$ to perform the calculations storing snapshots every 0.1yr. The raw data contains two of these data sets for the canonical S-star Cartesian coordinates as a function of time, and one set in which one star (S5) was displaced in the positive x-direction by $10^{-10}$ relative to it's current (1 Jan 2021) x-coordinate. The calculation are performed within the AMUSE framework (2013CoPhC.183..456P). Main conclusions from the paper and supported by our analysis of the data. -The S-star cluster around the supermassive black hole has a Lyapunv time scale of about 450 years. -The S-star cluster does not resembler a "Solar system" because of the orbits have a wide range in eccentricity and inclination. -Chaos in the S-star cluster is driven by close encounters between stars, which happend to be near the supermassive black hole. -The close near-black-hole encounters lead to the brownian motion of the black hole, which is reflected in changes in the S-star orbits. -minitious differences in initial conditions lead to slightly different close encounters, which drive differences in the details of the black hole's Brownian motion. more details in README.md Running the scripts requires the Astrophysical Multipurpose Software Environment (AMUSE for short). AMUSE can be downloaded from git through:https://github.com/amusecode/amuse see https://www.amusecode.org/ for a more extensive description. The data is organized in files in directories. Files and directories: REDME.md # this file data_raw # raw data in AMUSE hdf5 format. data_processed # processed data files, typically in python pickle binary format src # contains the script for running Brutus in AMUSE figures # processed figures in pdf format generated from the scripts plot # plotting
2023 · Strasbourg Astronomical Data Center · dataset
Solar siblings search with APOGEE and Gaia DR2 ↗Free copyStellar, planetary, and galactic studies
2023 · Leiden Repository (Leiden University)
Modeling evolution from gas to young massive star clusters ↗Free copyFree PDF ↗Astrophysics and Star Formation Studies Abstract
Despite their pervasive influence, many aspects of star cluster formation are poorly understood because they are difficult to model. Simulation of their formation requires modeling a multitude of physical processes, from magnetohydrodynamics (MHD) to stellar feedback and gravitational dynamics, on scales from binary orbits to the widths of molecular clouds. To address these issues, we use Torch: a code employing the Astrophysical Multipurpose Software Environment (AMUSE) framework to couple stellar evolution and N-body codes with the MHD code FLASH. We include star formation based on sampling of the initial mass function after sink particle accretion, ray-tracing for ionizing and non-ionizing radiation, and mechanical feedback in the form of winds and supernovae. Torch originally required excessive computational resources to model giant molecular clouds (GMCs) with masses exceeding 105 M☉, as it could not evolve the hundreds of thousands of stars that form in more massive clouds. This left a considerable gap, as the most massive GMCs in our galaxy exceed 106 M☉. To enable Torch to model more massive GMCs, we integrate the N-body code PeTar to more efficiently handle the stellar dynamics. We present results from new Torch simulations of star clusters forming from clouds of mass 104, 105, and 106 M☉. The most massive GMC forms over 100,000 stars within the first million years, making it one of the largest star cluster formation models resolving individual stars ever computed. We compare the global properties of each forming cluster over time and consider which remain constant as cloud mass is increased. We present the star formation histories and the time evolution of the gas properties, cluster mass, half-mass radius, and stellar velocity dispersion for each cloud.