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Simon Portegies Zwart

Publications and source records attributed to Simon Portegies Zwart.

At least 19 recordsLinked to original sources
arXiv2026

Star Cluster Ecology VIII. -- Dynamically Forming S-Type and $α$Centauri-like Systems

Aims: To analyse the impact of dynamically formed binaries emerging naturally from various star cluster environments on already established planetary systems. Methods: Numerical simulations replicating the star-forming region NGC 1333 are conducted. We consider three models, each using identical cluster realisations and simulation parameters. The cluster itself is initially sub-virial and fractally distributed. Model~A assumes planetary systems are initially in mean motion resonance. In Model~B, the same planetary systems are moved out of resonance, but remain intrinsically stable. Finally, Model~C removes all planets from the simulation. Ten independent realisations are integrated per model until 30 Myr. Results: Dynamically formed binaries emerge at similar rates across models, indicating planets play little role in their formation. We also find a higher production rate of wide binaries compared to previous numerical studies which we attribute to the sub-virial and sub-clustered initial conditions. S-type and binary S-type planetary systems naturally emerge in our simulations, while P-type systems are rare. For Model~A, the fraction of S-type or binary S-type systems is f_{\rm S}=0.02 and $f_{\rm Bin,\, S}=0.05, respectively. Rogue planets originating from a binary system are ejected with a substantially larger velocity than those around singletons. Planet-star collisions and planet capture events occur disproportionately within binary systems. Finally, several \alphaCentauri-like systems emerge in our simulations, suggesting that the nearest stellar system to the Sun may have a dynamical origin.

astro-ph.EP↗
arXiv2026

A triple-induced merger in T Ori C, solves the proplyd lifetime problem and the curiously young shell of M42

There has long been a tension between the stellar ages in the Orion Nebula Cluster and the rapid external photoevaporation of its protoplanetary discs. Recently, the shell of the Orion Nebula has similarly been found to be dynamically younger than the stars. We propose a new scenario to resolve both age problems. In our scenario the ONC's most massive star, $θ^1$~Ori~C1, formed from the merger between two binary stars induced by vZLK oscillations due to the present-day binary companion $θ^1$~Ori~C2. This merger, happening between the last episode of star formation and today, resulted in an increased luminosity, leading to stronger external photoevaporation and accelerated expansion of the shell. {We use Monte Carlo simulations to explore both whether a sudden brightening of $θ^1$~Ori~C1 could reconcile the stellar ages and shell expansion, and whether triple progenitors to $θ^1$~Ori~C\, could result in stellar mergers on the relevant timescale. A sudden brightening of $θ^1$~Ori~C1 a few hundred thousand years ago can reproduce today's shell while maintaining a system age close to the stellar age. However, the required increase in stellar wind luminosity is greater than a simple merger can explain. At lower luminosity, the mixing of a relatively greater amount of cool photoevaporative wind material into the hot bubble could result in the required increase, and we identify a lower limit on the required strength of this effect. Additionally, we find that progenitor triples merge readily, on timescales even shorter than the scenario would require. These mergers could be deferred by increased pre-main sequence tidal effects, rotation, and perturbing encounters with other cluster members. Our proposed scenario with a merger driven by von Zeipel-Lidov-Kozai evolution solves two problems; the Orion Nebula's proplyd problem and the shell lifetime problems.

astro-ph.GA↗
arXiv2026

Validating direct solvers for Newton's gravitational N-body problem, and the systematic comparison between IEEE floating point and Posits

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.

physics.comp-ph↗
arXiv2026

Planet-moon ejections in close stellar encounters

Free-floating planet-moon pairs (FFPMs) may form when planetary systems experience close stellar encounters. We quantify moon-retention probabilities and ejection cross sections for planets and planet-moon systems subject to close stellar encounters, and to dentify the orbital conditions most favorable for forming FFPMs. 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. FFPM cross-sections depend on the moon semi-major axis $a_m$, decreasing gradually until a drop near $a_m\sim0.45\,R_H$. Planet-only ejection cross-sections instead decline steadily with $a_p$. Io-like moons ($a_m = 0.008\,R_H$) survive, but survival falls beyond $0.4\,R_H$. Compared with planet-planet scattering, stellar encounters preserve moons more effectively across all separations. Surviving moons at $a_m\lesssim 0.4\,R_H$ retain near-circular, low-inclination orbits, while wide-orbit moons show stronger dynamical excitation. Applying our cross-sections to the microlensing system MOA-2011-BLG-262Lb suggests possible progenitor semi-major axes between $a_p \sim 1.3$\,au and $\sim 5.9$ au for a solar-mass host. Uncertainties remain large and the probability distribution is flat but we prefer $a_p \sim 5.2$\,au. Stellar-encounter ejections constitute a viable channel for producing FFPMs whose orbital properties differ from those formed by planet-planet scattering. Moon retention and orbital excitation provide promising diagnostics of ejection history. Current and upcoming microlensing and direct-imaging surveys may be capable of detecting Galilean-mass moons around rogue planets, offering new tests of dynamical formation pathways.

astro-ph.EP↗
arXiv2026

Recoiling Black Holes I. Burst of Observables

We aim to investigate the tidal disruption and gravitational wave events shortly after a massive black hole binary merges in the galactic centre and whose remnant black hole is ejected from the galaxy. Using computational methods, black holes of mass $M_{\bullet}=10^{5}$ M$_\odot$ and $4\times10^{5}$ M$_\odot$ embedded in a nuclear star cluster are kicked at velocities of $v_k=300$ and $600$ km s$^{-1}$. Systems are integrated for $0.1$ Myr using a $4$th-order Hermite scheme. 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 lower $v_k$, larger $M_{\bullet}$ and for steeper nuclear star cluster density profiles at moment of merger. Assuming binary black holes scour a Bahcall-Wolf density profile during coalescence, ejected remnants with mass between $10^{5}\leq M_{\bullet}$ [M$_\odot] \leq 4\times10^{5}$ generate observable offset events at a forecasted rate of $\dot{N}\lesssim290$ 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 $\dot{N}\lesssim30$ 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 provides test for numerical relativity.

astro-ph.HE↗
arXiv2026

ReLaTS: a Reinforcement Learning-based method for dynamically determining the coupling Time Step in multi-scale simulations of self-gravitating systems

Astrophysical simulations frequently address multi-scale, multi-physics problems through subsystem decomposition, problem-tailored integration schemes, and coupling on fixed manually set timescales. 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 \textit{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 multi-scale simulations.

astro-ph.IM↗
arXiv2026

Centrally concentrated star formation in young clusters II: Jet feedback

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.

astro-ph.GA↗
arXiv2026

Oort Cloud Ecology -- IV. Exchanging Asteroids

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

astro-ph.EP↗
arXiv2026

Life is But a Stream: The Distribution of Planetary Systems Along Stellar Streams and their Properties

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 centre of the stream have a higher chance of having planets pushed to eccentric orbits, 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 semi-major axis $a_0$ based on the star's location along a stellar stream $Δϕ$.

astro-ph.EP↗
arXiv2026

Kozai-driven mass loss of the circumbinary disk in D9 in orbit around the supermassive black hole Sgr A*

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 S-star binary, called D9, was found to be orbited by a circumbinary disk. Due to the gravitational interaction between Sgr A* and the binary, the disk could be short-lived. We investigate the evolution of the disk around a stellar binary while orbiting Sgr A*. We use the \texttt{AMUSE} framework for coupling a gravity solver (for the binary and Sgr. A*) with a hydrodynamics solver (for the disk). We find that, the disk eventually settles between 5.2$a_{\rm in}$ and 0.28 Hill radii of the binary. Here, $a_{\rm in}$ is the semi-major axis of D9. The inclination of the circumbinary disk follows the binary's, which evolves due to the von Zeipel-Lidov-Kozai (vZLK) mechanism induced by Sgr A*. The mean eccentricity of the disk is approximately in anti-phase with the eccentricity evolution of the binary. We find a vZLK timescale of $T_\text{vZLK}\approx62.5\,$kyr, which is two orders of magnitude shorter than the value reported by Peisker etal. (2024). As a consequence, D9 has undergone multiple vZLK oscillations in its lifetime of 2.7 Myr. We find 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. The secular evolution observed in both the binary and the disk are consistent with theoretical predictions. We find the disk loses $\sim$7\% $\pm$ 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 $\sim$4 Myr. D9 will then be $\sim$6.7 Myr old, which is on the same order as the current average age of S cluster members. The vZLK-driven mass loss could, therefore, explain the absence of Br$γ$ emission from other S cluster members.

astro-ph.GA↗
arXiv2026

Nemesis: A Multi-Scale, Multi-Physics Algorithm for Astrophysics

In this work, an updated version of the multi-scale, multi-physics algorithm, Nemesis which makes use of the Astrophysical Multipurpose Software Environment (AMUSE). The algorithm is formally introduced and validated. A suite of simulations is run 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. Nemesis is found to yield indistinguishable results in both the global and local scales when compared with the direct N-body code Ph4. The same conclusion is found when analysing its ability to capture the von Zeipel-Lidov-Kozai effect. When analysing its computational performance, the wall-clock time scales roughly as $t_{\rm sim \propto 1/ \sqrt{δt_{\rm nem}}$ where $δt_{\rm nem}$ represents the time synchronisation between the global and local scales. When changing 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, it's found that at worst, the computational time increases linearly with the number of excess systems. The method introduced here can find it's use in numerous domains of astronomy thanks to its flexibility and modularity, from simulating protoplanetary disks in star clusters to binary black holes in the galactic center.

astro-ph.IM↗
arXiv2026

The formation of periodic three-body orbits for Newtonian systems

Braids are periodic solutions to the general N-body problem in gravitational dynamics. These solutions seem special and unique, but they may result from rather usual encounters between four bodies. We aim at understanding the existence of braids in the Galaxy by reverse engineering the interactions in which they formed. We simulate self-gravitating systems of N particles, starting with the constructing of a specific braid, and bombard it with a single object. We study how frequently the bombarded braid dissolves in four singles, a triple and a single, a binary and 2 singles, or 2 binaries. The relative proportion of those events gives us insight into how easy it is to generate a braid through the reverse process. It turns out that braids are easily generated from encounters between 2 binaries, or a triple with a single object, independent on the braid's stability. We find that 3 of the explored braids are linearly stable against small perturbations, whereas one is unstable and short-lived. The shortest-lived braid appears the least stable and the most chaotic. nonplanar encounters also lead to braid formation, which, in our experiments, themselves are planar. The parameter space in azimuth and polar angle that lead to braid formation via binary-binary or triple-single encounters is anisotropic, and the distribution has a low fractal dimension. Since a substantial fraction of ~9% of our calculations lead to periodic 3-body systems, braids may be more common than expected. They could form in multi-body interactions. We do not expect many to exist for time, but they may be common as transients, as they survive for tens to hundreds of periodic orbits. We argue that braids are common in relatively shallow-potential background fields, such as the Oort cloud or the Galactic halo. If composed of compact objects, they potentially form interesting targets for gravitational wave detectors.

astro-ph.GA↗
arXiv2025

Transferring Data from a Voronoi Mesh to an Adaptive Cartesian Grid in Pursuit of Self-consistent Top-down Star Formation

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.

astro-ph.GA↗
arXiv2025

The significance of Halley's Comet in the Bayeux Tapestry

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.

physics.hist-ph↗
arXiv2025

Protostellar Jets in Star Cluster Formation and Evolution: I. Implementation and Initial Results

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 $= 2 \times 10^4$ M$_{\odot}$. We also find that the star formation rate of our lower mass clouds (M $= 5 \times 10^3$ M$_{\odot}$) 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.

astro-ph.GA↗
arXiv2025

Massive star cluster formation III. Early mass segregation during cluster assembly

Mass segregation is seen in many star clusters, but whether massive stars form in the center of a cluster or migrate there dynamically is still debated. N-body simulations have shown that early dynamical mass segregation is possible when sub-clusters merge to form a dense core with a small crossing time. However, the effect of gas dynamics on both the formation and dynamics of the stars could inhibit the formation of the dense core. We aim to study the dynamical mass segregation of star cluster models that include gas dynamics and self-consistently form stars from the dense substructure in the gas. Our models use the Torch framework, which is based on AMUSE and includes stellar and magnetized gas dynamics, as well as stellar evolution and feedback from radiation, stellar winds, and supernovae. Our models consist of three star clusters forming from initial turbulent spherical clouds of mass $10^{4,5,6}\rm~M_\odot$ and radius $11.7\rm~pc$ that have final stellar masses of $3.6\times10^3\rm~M_\odot$, $6.5\times10^4\rm~M_\odot$, and $8.9\times10^5\rm~M_\odot$, respectively. There is no primordial mass segregation in the model by construction. All three clusters become dynamically mass segregated at early times via collapse confirming that this mechanism occurs within sub-clusters forming directly out of the dense substructure in the gas. The dynamics of the embedded gas and stellar feedback do not inhibit the collapse of the cluster. We find that each model cluster becomes mass segregated within $2~$Myr of the onset of star formation, reaching the levels observed in young clusters in the Milky Way. However, we note that the exact values are highly time-variable during these early phases of evolution. Massive stars that segregate to the center during core collapse are likely to be dynamically ejected, a process that can decrease the overall level of mass segregation again.

astro-ph.GA↗
arXiv2025

Ripples spreading across the Galactic disc. Interplay of direct and indirect effects of the Sagittarius dwarf impact

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. This study aims 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. We perform high-resolution $N$-body simulations 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. Our simulations demonstrate that the satellite's perturbation directly excites the bending mode and induces spiral arms in the galactic disc. These spiral arms 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 regions. The simulations 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. Our findings highlight the combined effects of direct satellite perturbations and indirect spiral arm dynamics in shaping the vertical structure of the MW disc.

astro-ph.GA↗
arXiv2025

Why Wide Jupiter-Mass Binary-Objects Cannot Form

The discovery of $N_{\rm pp} = 40$ Jupiter-mass binary objects (JuMBOs) alongside $N_{\rm p} = 500$ free-floating Jupiter-mass objects (JMOs) in the Trapezium cluster's central portion raises questions about their origin \cite{2023arXiv231001231P}. \citet{2024NatAs...8..756W} argue that the rate at which two planets orbiting the same star are stripped by a close encounter can explain about half the observed JuMBOs in the Trapezium cluster. Although, their cross-section calculations agree with our own \citep{2024ScPA....3....1P}, one cannot extrapolate their results into clustered environments because it ignores the dissociation of JuMBOs due to subsequent encounters in the clustered environment. The inability of forming JuMBOs via the proposed scenario either calls for another formation mechanism, or the observed JuMBOs require thorough confirmation.

astro-ph.EP↗