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Gravitational waves (GWs), ripples in spacetime generated by dynamic astrophysical systems, provide a unique tool for exploring extreme environments in the universe. This thesis focuses on GWs emitted by massive compact binary systems, such as binary black holes (BBHs) and binary neutron stars (BNSs), and neutron star-black hole (NSBH) pairs during their inspiral, merger, and ringdown phases. These waves carry detailed information about the binary’s mass, spin, and orbital dynamics, offering insights into the nature of gravity and dense matter. By leveraging observational data from LIGO, Virgo, and KAGRA, alongside advanced simulations, the study aims to enhance parameter estimation precision and unravel the astrophysical origins of such binaries. Key findings include constraints on stellar evolution, compact object formation, and dense matter physics, exemplified by events like GW170817, which confirmed kilonovae associated with BNS mergers. This research contributes to gravitational wave astronomy by advancing our understanding of fundamental physics and the dynamics of the most extreme cosmic phenomena.

Over the last two decades, photometry and spectroscopy have revolutionized our understanding of globular clusters (GCs), revealing their complexity and the presence of multiple stellar populations (MPs), together with a wealth of information on their properties. Studies reveal that MPs are a ubiquitous characteristic of GCs, although each GC is unique. Nonetheless, how the MPs form and evolve remains an open question. Since different formation mechanisms of the different populations leave a kinematic signature, we observe kinematic variation across the GCs radii. Thus, kinematic and dynamic information is the key to finding an answer to the origin of the MPs. Due to long relaxation times, GCs still retain signatures of the multiple population’s formation mechanisms in the external regions. Our study aims to perform a kinematic study in the central and external regions for a complete kinetic understanding of GCs based on new and archival HST data. In this poster, we will present the first results of the high-precision proper motion study of the MPs of the central and external regions of the galactic GC M15.

M67 is a dynamically evolved old open cluster in the Milky Way. Due to its nearness and relatively low levels of dust in the line-of-sight, it has been extensively observed. We perform N-body simulations of the old open cluster M67 (NGC 2682), originally modelled by Hurley et al. (2005) using NBODY4. These new simulations use the updated NBODY6++GPU and are also compared to observational data from the Gaia survey.

Recent observations have shown globular clusters to be systems of greater kinematic and morphological complexity than can be described using spherical non-rotating dynamical models. A new family of self-consistent models for quasi-relaxed stellar systems are presented, treating for the first time the case of asynchronous rotation within an external tidal field. Constructed as a double perturbation expansion of the classical King models, the resulting free boundary problem is solved via the method of matched asymptotic expansion. These models are found to possess a triaxial structure whose aspherical distortion increases with increased asynchronicity. It is hoped these models will provide a more realistic equilibrium description for use in investigations of cluster structure and kinematics.

The study of star cluster evolution necessitates precise modeling of their density profiles. Observa- tional evidence indicates that many star clusters follow a Plummer density profile, which is therefore frequently used in modeling efforts. However, most studies have focused on the post-gas-ejection phase, overlooking the influence of gas on early dynamical evolution. This work investigates the evolution of star clusters embedded within gas clouds, particularly those with a centrally concentrated gas profile, which has not been extensively explored. Simulations were conducted using the Torch environment, integrating the FLASH magnetohydrodynamic code into the AMUSE multipurpose astrophysical frame- work. This permits detailed modeling of star formation, stellar evolution, dynamics, radiative transfer, and magnetohydrodynamics. Simulations were performed of the collapse of a centrally concentrated turbulent sphere of mass 2513 M⊙ with varying initial stellar mass and numerical resolution. The key conclusions from this study are: subclusters are formed even in dense gas clouds; the final stellar density profile is consistent with a Plummer profile, but one that is more centrally concentrated than analytically predicted; stars remain tightly bound for extended periods; and gas ejection is only converged in our highest resolution models.

Though IMBHs remain undetected, strong indirect evidence points to their presence in globular cluster cores like ω Centauri. Their detection is hindered by dense stellar environments, but future GW observatories may identify them through GW signals from IMBH–SBH binaries. This study explores how such binaries form, focusing on their formation rate as a function of the clusters’ properties.

Young star clusters can inherit bulk rotation from the molecular clouds from which they have formed. This rotation can affect the long-term evolution of a star cluster and its constituent stellar populations. In this study, we aim to characterize the effects of different degrees of initial rotation on star clusters with primordial binaries. The simulations are performed using NBODY6++GPU. We find that initial rotation strongly affects the early evolution of star clusters. Rapidly-rotating clusters show angular momentum transport from the inner parts to the outskirts, resulting in a core-collapse. Angular momentum transport is accompanied by a highly elongated bar-like structure morphology. The effects of bulk rotation are reduced on the timescale of two-body relaxation. Rotating and non-rotating clusters experience changes in the direction of angular momentum near the dissolution and early evolution due to the tidal field, respectively. We present synthetic observation of simulated clusters for comparison with future observations in filters of Gaia, CSST, and HST. This work shows the effects of bulk rotation on systems with primordial binaries and could be used for identification of rotation signature in observed open clusters.

I present the current sytatus of the Startrack poulation sysnthesis code. we are moving to the model of general availability and we present the updates that are not wbeing done to the Synthetic Universe databse.

We present a high-resolution near-infrared spectroscopic analysis of 60 red supergiant (RSG) candidates from six RSG clusters (RSGCs) in the Scutum complex, using the Immersion Grating Infrared Spectrograph (IGRINS). While most stars in these clusters exhibit coherent kinematic signatures (radial velocities around 100 km/s), stars in RSGC4 stand out with a broad radial velocity dispersion (–64 to +115 km/s). Photometric indices (Q_GK_s > 1.7) and spectroscopic features suggest that a significant number of RSGC4 candidates are early AGB stars rather than true RSGs. Four candidates in RSGC4 show mid-infrared excesses and absorption features that are absent in other candidates. Notably, two of these four candidates exhibit absorption features indicative of D-type symbiotic stars, along with multi-epoch radial velocity variations. Proper motion analysis reveals no evidence of runaway or walkaway stars in RSGC4. The dynamical properties highlight that RSGC4 and RSGC1 deviate from the disk-like motions observed in other clusters: RSGC4 exhibits low normalized horizontal and vertical actions and high orbital eccentricities, while RSGC1 displays high vertical actions and inclinations. We propose that RSGC4 may not be a gravitationally bound cluster, but rather a chance alignment of evolved stars along the line of sight at similar distances. Our results emphasize the complexity of star formation environments in the inner Galaxy and call for a reevaluation of cluster identification criteria in crowded bulge regions.

The direct N-body method is a conventional tool for investigating the dynamics of stellar systems. Combined with stellar evolution models, it is widely used to model isolated star clusters. However, to realistically depict star clusters embedded within galaxies, it is necessary to account for hydrodynamic effects and galactic environments, such as ongoing star formation, feedback, and dark matter potential. We develop the Enzo-Abyss project to integrate a direct N-body code (Abyss) into a hydrodynamic simulation (Enzo). Abyss is a newly developed direct N-body code using Hermite 4th order integrator, combined with the few-body group integrator SDAR and the stellar evolution code SEVN. By introducing our novel background acceleration technique, we can describe the evolution of stellar systems interacting with dark matter and gas particles inside a galaxy. As the initial applications, we are focusing on the formation of nuclear star clusters and the evolution of IMBHs in dwarf galaxies with star-by-star formation and feedback routines.

Future gravitational wave observatories can probe dark matter by detecting the dephasing in the waveform of binary black hole mergers induced by dark matter overdensities. Such a detection hinges on the accurate modelling of the dynamical friction, induced by dark matter on the secondary compact object in intermediate and extreme mass ratio inspirals. We present simulations paper with NbodyIMRI, a new publicly available code designed for simulating binary systems within cold dark matter `spikes’. Leveraging higher particle counts and finer timesteps, we validate the applicability of the standard dynamical friction formalism and provide an accurate determination of the maximum impact parameter of particles which can effectively scatter with a compact object, across various mass ratios. We also show that in addition to feedback due to dynamical friction, the dark matter also evolves through a `stirring’ effect driven by the time-dependent potential of the binary. We introduce a simple semi-analytical scheme to account for this effect and demonstrate that including stirring tends to slow the rate of dark matter depletion and therefore enhances the impact of dark matter on the dynamics of the binary. Moreover we perform additional simulations where we constrain the interplay of post-Newtonian corrections (up to order 2.5 in $c^2$) and relativistic dynamical friction. 2) Aims. The Fornax dwarf spheroidal galaxy (dSph) represents a challenge for some globular cluster (GC) formation models, because an exceptionally high fraction of its stellar mass is locked in its GC system. In order to shed light on our understanding of GC formation, we aim to constrain the amount of stellar mass that Fornax has lost via tidal interaction with the Milky Way (MW). Methods. Exploiting the flexibility of effective multi-component N-body simulations and relying on state-of-the-art estimates of Fornax’s orbital parameters, we study the evolution of the mass distribution of the Fornax dSph in observationally justified orbits in the gravitational potential of the MW over 12 Gyr. Results. We find that, though the dark-matter mass loss can be substantial, the fraction of stellar mass lost by Fornax to the MW is always negligible, even in the most eccentric orbit considered. Conclusions. We conclude that stellar-mass loss due to tidal stripping is not a plausible explanation for the unexpectedly high stellar mass of the GC system of the Fornax dSph and we discuss quantitatively the implications for GC formation scenario

White dwarfs in dense stellar environments provide unique laboratories to test fundamental physics under extreme gravitational fields. In this study, we use ultraviolet spectral observations of the Ni V ion in the compact white dwarf G191-B2B, obtained with the \textit{Hubble Space Telescope Imaging Spectrograph} (HSTIS), combined with high-precision laboratory data, to probe possible variations in fundamental constants. We constrain the rate of change of the gravitational constant to \[ \dot{G}/G = (-0.014 \pm 0.016) \times 10^{-15} \text{yr}^{-1} \] in a gravitational potential \(\phi \approx 10^{4}\) times stronger than terrestrial conditions, with an average Ni V gravitational redshift of \[ z_{\text{abs}} \approx 8.47 \times 10^{-5}. \] These results provide new constraints on potential deviations from General Relativity and extensions of the Standard Model in compact objects, reinforcing the role of white dwarfs in dense stellar systems as natural laboratories for testing new physics. Our findings also highlight the potential of multi-wavelength observations to probe the interplay between compact-object dynamics and fundamental physics in dense astrophysical environments.

Omega Centauri is the most massive globular cluster within the Milky Way. Dynamical measurements of the cluster suggest the presence of ~10,000 stellar mass black holes at the center. However, so far there is no direct observational evidence for even a single stellar mass black hole in the cluster. We present a new search for stellar mass black holes at the center of Omega Centauri, using gravitational microlensing. Because Omega Centauri is a calibration target for the Hubble Space Telescope, there is a unique and rich imaging dataset consisting of hundreds of individual observations taken over the last 12 years, and there are more than 180,000 stars with well-sampled (N>100) lightcurves. Within these lightcurves, we are searching for microlensing events caused by a stellar mass black hole, which can brighten a star that passes behind it in the cluster. We present modeling of this data using new simulations of the cluster, a completeness analysis using synthetic events, and a first list of interesting candidate events.

Recently, there have been a significant number of detections of binary black hole (BBH) mergers. This suggests an abundant population of unmerged BBHs with wide separations, although they remain undetected. We consider star-BBH triples and propose to search for hidden BBHs in such systems indirectly, by examining the anomalous motions of the tertiary stars. We demonstrate that short- and long-term radial velocity (RV) modulations of stars can indeed reveal the presence of unseen BBH companions, if they exist. As a proof-of-concept, we apply our method to a star-dark companion binary candidate, Gaia BH1, which was recently discovered through Gaia astrometry. Our analysis shows that precise follow-up RV monitoring could provide a promising method for discovering star-BBH triples in the future.

We report the discovery of a septuple open cluster system in Gaia DR3 data, identified through agglomerative clustering analysis. The system comprises seven clusters—ASCC 19, ASCC 20, ASCC 21, Briceno 1, OC 0339, OCSN 61, and UBC 17a—each separated by an average distance of less than 50 parsecs. Cluster membership was refined using the Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) algorithm on Gaia DR3 astrometric data, centered at right ascension 83◦ and declination 1◦, within a 5◦ radius. Membership probabilities were assessed via consistency checks, a Gaussian-Uniform Mixture Model (GUMM), and Kernel Density Estimation (KDE). These clusters occupy a tight locus in the G versus BP–RP color–magnitude diagram, indicating a coeval population. Notably, UBC 17a exhibits a bimodal parallax distribution, suggesting substructure. To investigate further, we extracted all stars within 100 pc of each cluster center and applied a Bayesian-Xtreme Deconvolution Gaussian Mixture Model (XDGMM) to trace tidal tail extensions. In the field of UBC 17a, two overdensities were identified: the known UBC 17b and a new, uncatalogued candidate—hereafter the UBC 17 Family. Despite broader proper motion dispersion and slightly greater separations (>50 pc), both substructures align on the CMD and show comparable isochrone ages (log Age ≈ 7.1–7.4). Monte Carlo–sampled orbit integrations using gala, incorporating astrometric uncertainties, show that all nine clusters have remained co-moving over the past 20–30 Myr within their error envelopes, supporting a common formation scenario. Ongoing analysis of their tidal tails may reveal new insights into the gravitational dynamics shaping this rare nine-cluster association.

Predicting the long-term stability of hierarchical three-body systems is a key challenge in celestial mechanics. Traditional stability criteria using the empirical parameter $Q = q_\mathrm{out}/a_\mathrm{in}$, which is the ratio of the outer pericenter distance to the inner semi-major axis on the initial orbit, have been widely used. However, their predictive accuracy is limited within the “mixed region”, where stable and unstable systems coexist even for the same $Q$ value. To address this problem, we performed $N$-body simulations for numerous hierarchical three-body systems and analyzed the time evolution of their orbital elements in detail. As a result, we found a strong correlation between the long-term stability of the systems and the periodicity of their orbits, observing specifically that unstable systems tend to exhibit lower periodicity in the mixed region. Based on this discovery, we developed a new stability criterion that quantifies orbital periodicity using Fourier analysis. We confirmed that out criterion significantly improves the classification accuracy between stable and unstable systems in the mixed region compared to the $Q$ parameter, which relies solely on the initial orbits. Our approach is a new quantitative stability assessment method based on $N$-body simulations and dynamical analysis, contributing to the improvement of long-term stability prediction accuracy.

Wide-field photometry of Galactic globular clusters (GCs) has been investigated to overcome the limitations imposed by the Hubble Space Telescope’s small field of view in studies of multiple populations. In particular, ground-based photometry has enabled the construction of chromosome maps (ChMs), allowing the identification of first- and second-generation (1G and 2G) stars over a wide field. The ChMs provide a means to determine the fraction of distinct populations across the observed field of view. In this study, we present the radial distribution of the 2G fraction in 29 GCs. We find that all clusters exhibit either a flat distribution or a centrally concentrated 2G population. Notably, the fraction of 1G stars beyond the half-light radius exhibits a clear bifurcation across all mass ranges. This suggests that a subset of GCs with lower 1G fractions (hereafter Group II) has undergone efficient loss of 1G stars in their outermost regions. Moreover, in relation to the radial distribution trends, most Group II GCs exhibit spatially mixed populations, whereas only the less massive clusters in Group I (those with higher 1G fractions) show that feature. Finally, we explore potential connections between these two groups and host cluster parameters. We find that most Group II GCs span a broad range of galactocentric distances but have smaller perigalactic distances (<3.5 kpc). Furthermore, analysis using Gaia data reveals that Group II clusters have higher energy in integrals of motion diagrams compared to Group I clusters.

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Variability studies offer a compelling glimpse into black hole dynamics, and Neutron Star Interior Composition Explorer’s (NICER’s) remarkable temporal resolution propels us even further. NICER observations of an active galactic nucleus (AGN), NGC 4051, have charted the geometry of the emission region of the central supermassive black hole. Our investigation of X-ray variability in NGC 4051 has detected extreme variations spanning a factor of 40–50 over a mere 10–12 hr. For the first time, we have constrained the X-ray power spectral density (PSD) of the source to 0.1 Hz, corresponding to a temporal frequency of 104 Hz in a galactic X-ray binary with a mass of 10 M⊙. No extra high-frequency break/bend or any quasiperiodic oscillations are found. Through detailed analysis of energy-dependent PSDs, we found that the PSD normalization, the high-frequency PSD slope, as well as the bending frequency remain consistent across all energies within the 0.3–3 keV band, revealing the presence of a constant temperature corona. These significant findings impose critical constraints on current models of X-ray emission and variability in AGN.

We present an integrated-light spectroscopic study of 7 young massive clusters (YMCs) in the Antennae galaxies. The optical spectra of the YMCs obtained with the GMOS-S attached to the 8.1-m Gemini South telescope reveal the spectral features dominated by massive stars, e.g, the continuum slope, the strength of the Balmer jump, and the broad emission lines originating from Wolf-Rayet stars. We analyze the observed spectra by means of the synthetic spectra generated from a simple stellar population model, obtaining the physical parameters of the YMCs, such as reddening, ages, total stellar masses, and the underlying stellar initial mass functions. The YMCs are younger than 10 Myr, and they contain stellar masses ranging from 10^5 M_sun to 10^8 M_sun. Interestingly, very massive clusters (> 10^6 M_sun) tend to have bottom-heavy mass functions. Although further studies of more stellar clusters in different environments are needed, our results support a variation of the stellar initial mass functions.

We present a detailed study of over 100 X-ray sources in the globular cluster Terzan 5, leveraging over a decade of Chandra observations. Terzan 5 has the highest interaction rate among all the galactic globular clusters, and the largest number of known quiescent neutron star low-mass X-ray binaries (qLMXBs). Our analysis includes photometry, spectral modeling, and variability studies. We identify over 20 qLMXBs in Terzan 5, reaching down to quiescent luminosities not previously probed in globular clusters. We find spectral evidence that one qLMXB has a helium, rather than hydrogen, atmosphere, suggesting that the neutron star accretes from a white dwarf. We also identify 30 variable sources, and find one new secure X-ray counterpart to a redback millisecond pulsar in Terzan 5.

The discovery of the ubiquitous nature of the multiple populations (MPs) in globular clusters (GCs) in our Galaxy and nearby galaxies is a great achievement in the near field cosmology. One of the remarkable aspects of the GC MPs is that the second generation (SG) of stars, showing the chemical compositions that experienced proton capture processes at high temperature and being the major component of the most of normal GCs with MPs, formed in more spatially concentrated inner regions of GCs out of interstellar media polluted by the first generation (FG) of stars, with the chemical compositions similar to abundance patterns observed in Galactic field stars with the similar metallicity. Over the past decades, we developed a new photometric system to study such lighter elemental abundance anomalies in GC MPs. With our system, we will be able to simultaneously measure accurate [Fe/H], [C,N,O/Fe] and helium abundance, which are the barometers of GC MPs, for the complete sample in crowded regions. In our talk, we will discuss the current status and the future perspective of our long-term survey program.

We present a spectroscopic method of modeling and identifying equal-mass binary systems with Neural Network (NN). The method is a Gaussian mixture model which identifies binaries by modeling the discrepency between NN-predicted and the geometric absolute magnitudes from Gaia parallaxes. With DESI Year-1 data release, we have identified 120,000 possible binaries, and discover that the binary fraction increases with [Fe/H] and $\log g$ and declines with [$\alpha$/Fe] and $T_\mathrm{eff}$, indicating stars with high Fe and low $\alpha$, which form early, may have experienced more encounters and tidal effects to disrupt binaries.

The ongoing discovery of new globular clusters (GCs) in the inner Milky Way has emphasized the need for follow-up spectroscopic studies. In this context, recent advancements in near-infrared (NIR) spectroscopy are opening new opportunities for investigating GCs and their stellar populations, particularly in highly obscured regions such as the Galactic bulge. Bulge GCs serve as crucial tracers of the Milky Way’s formation history, preserving fossil records of its early evolutionary phases. We have conducted high-resolution NIR spectroscopic observations of both optically well-studied GCs and newly identified GC candidates using the IGRINS and IGRINS-2 instruments at the Gemini-South and Gemini-North observatories. Our results confirm that IGRINS/IGRINS-2 offer powerful capabilities for advancing our understanding of the dynamical and chemical properties of GCs. Among our targets, Gran 5—a recently identified low-mass GC near the Galactic center—shows particularly intriguing results. Our analysis reveals the presence of two distinct stellar populations within Gran 5, with mean metallicities of [Fe/H] = −0.76 dex and −0.55 dex, respectively. This represents the first detection of multiple stellar populations with different metallicities in a low-mass GC. In this talk, I will present our ongoing high-resolution NIR spectroscopic survey of bulge GCs and discuss how these observations enhance our understanding of the formation and evolution of GCs and the Milky Way.

The presence of old open clusters but remaining rich in members challenges the conventional view that such systems dissociate within 1 Gyr in the typically inhospitable Galactic disk. We present a study of eight such clusters—Collinder 261, NGC 2158, NGC 2477, NGC 2506, NGC 6791, NGC 6819, NGC 7786, and Trumpler 5—each with an age comparable to those of globular clusters yet harbors thousands of members. Using Gaia DR3, we determined the most reliable member list so far for these clusters, hereafter fitting the post-main sequence members with the isochrones model to derive their ages. For example, NGC 6791, with a cluster radius of 19.0 arcmin and more than 5000 members, lies 4.4 kpc away and has an age of 8.5 Gyr, confirming the longevity and rich membership. With a comparison sample of “false positives”, i.e., stars way outside the cluster region yet sharing the same proper motion and parallax ranges, the derived luminosity function and hence the mass function shows a top-heavy trend, differing significantly from the canonical form. Most of these clusters exhibit advanced positional and kinematic mass segregation. We propose a possible explanation for the survival of these elusive clusters to be their relative orbital isolation from the Galactic disk perturbation.

Most massive galaxies, including the Milky Way typically host both a supermassive black hole (SMBH) and a nuclear stellar cluster (NSC). This environment affects the evolution of binaries via frequent close encounters with the surrounding stars of the NSC as well as secular processes related to the SMBH, such as Eccentric-Kozai-Lidov (EKL) oscillations. Due to the distance and extinction from dust, solar and sub-solar mass main-sequence (MS) stars are not visible for observations and therefore constitute an invisible population of stars in the NSC who’s binaries could have a key role in formation of dusty cloud-like G-objects. This is supported by previous numerical simulations and the recent observation of a $\sim 2\mathrm{M}_\odot$ spectroscopic binary in the vicinity of the S-cluster. We aim to understand how MS stars at the hard/soft boundary (H/SB) evolve dynamically, and how a region where dynamical processes operate on similar timescales shape their outcome. We simulate more than $6\times10^7$ three-body encounters (binary + tertiary) for a total of 5736 binaries, which incorporate EKL oscillations, tidal circularisation and stellar collisions. In this way we follow the dynamical evolution of binaries ($\leq 2\mathrm{M}_\odot$) near the H/SB limit at $0.1\mathrm{pc}$ ($0.3\mathrm{pc}$) from the SMBH in a steady-state model of the NSC. Consistent with previous studies, a majority, 80\% (60\%), of binaries still merge or evaporate within $1\mathrm{Gyr}$ ($2\mathrm{Gyr}$) but a substantial fraction, 10\% (23\%), of our binaries remain intact throughout the simulation, $\geq10 \mathrm{Gyr}$, due to outward migration. Furthermore we find that \textit{i)} $\sim 1\%$ of our binary merger products’ orbits originating at $0.1\mathrm{pc}$ contaminate the orbits of the S-cluster stars, \textit{ii)} $\sim1\%$ of the mergers occur late enough ($\lesssim 10\mathrm{Gyr}$) that they should not have evolved significantly at present day, and as such may appear as young metal poor main sequence stars or red giant stars, \textit{iii)} $80\%$ of collisions between surrounding stars and our binaries leads to three-body pile ups (all three stars merge), virtually all of these occur within the first few $10^8$ years with a maximum rate of $\sim 0.1 \mathrm{Gyr}^{-1}$. Our work demonstrates the importance of studying the details of low-mass binary evolution and dynamics in galactic nuclei in order to reveal the full complexity of this environment and its peculiar objects.

Blue straggler stars (BSSs) are anomalous main-sequence stars that appear brighter, bluer and younger than expected, often observed in star clusters. The efficiency of their formation mechanisms depends on the properties of their host cluster. Leveraging this, BSSs can give us hints on what hides at the center of star clusters. In my talk, I will focus on the effect of a central intermediate-mass black hole (IMBH, m=10^2-10^5 Msun) or a black hole subsystem (BHS) on the production and properties of BSSs. To carry out this analysis, I used the results from the MOCCA-Survey Database I, which contains more than a thousand realizations of globular clusters (GCs) with varying masses, densities and Galactocentric distances. I find that GCs with an IMBH or an “old” BHS (i.e., a BHS that has already interacted with the outer regions of the cluster) can host more than 100 BSSs, which tend to be concentrated within the central 10 parsecs. In contrast, GCs containing “young” BHSs tend to host fewer BSSs, which are distributed more uniformly. Furthermore, I will show how observational constraints on GCs central radii and BSSs contained within them provide a powerful discriminant between clusters with an IMBH and clusters with a BHS.

Pulsars and millisecond pulsars (MSPs), known for their periodic electromagnetic emissions, serve as precise cosmic clocks and valuable tools in studying dense matter physics and general relativity. In this study, we focus on the numerical simulation of pulsars within globular clusters using the advanced Nbody6++GPU simulator. Our goal is to model the spin and magnetic field evolution of these objects in the unique environment of globular clusters. Preliminary results highlight the significant role of binary interactions in the recycling process and the evolution of these compact stars. The Nbody6++GPU simulator proves to be an effective tool for deep analysis, providing insights into the intricate dynamics of pulsar evolution. This research is ongoing and aims to further refine the understanding of pulsar behavior in dense stellar environments. Keywords: Pulsars, Millisecond Pulsars, Numerical Simulations, Magnetic Field, Spin, Globular Clusters

Globular clusters (GCs), recognized for their high stellar densities and frequent dynamical interactions, offer a compelling environment for studying compact binaries. In this talk, I will present findings from a detailed comparison of Monte Carlo simulations and observational data, demonstrating how the dynamical state of GCs shapes the formation, evolution, and disruption of these systems. I will discuss the key parameters used in the Monte Carlo approach, the observational techniques employed, and the principal conclusions drawn from this work. These results deepen our understanding of dense stellar environments, revealing how intrinsic dynamical processes shape compact binary populations.

We present results from direct N-body simulations of the inner parsec of the Milky Way. We focus on the interaction of putative intermediate-mass black holes (IMBHs) with the surrounding stellar system. In particular, we show how an IMBH can affect the distribution of stars in the young stellar disk. We demonstrate that an IMBH with a mass greater than 10^4 M⊙ can efficiently merge with the central supermassive black hole within a Hubble time. We discuss whether such a merger could have occurred in the Milky Way within the past 100 Myr.

Modern gravitational wave (GW) detectors primarily utilize electromagnetic waves (EMWs) in the geometric optics regime. Geometric optics is applicable when the wavelength of the EMWs is much shorter than the characteristic scale of spacetime curvature or variations in the medium. In this work, we explore the potential of using EMWs beyond the geometric optics regime for GW detection. To this end, we directly solve the perturbed Maxwell equations. Obtaining solutions requires appropriate boundary conditions. We propose suitable boundary conditions, formulated in terms of gauge-invariant quantities, to ensure experimental controllability. Decomposing a general electromagnetic (EM) field into phase and amplitude components is not straightforward. Therefore, we propose using the stress-energy tensor of the EM field as an observable physical quantity for perturbed EMWs. We derive the stress-energy tensor for the perturbed EM field from first principles and investigate its properties. Based on this, we present several scenarios in which such methods may be applied to GW detection.

The detection of gravitational wave events has significantly contributed to understanding compact objects like Binary Black Holes (BBH), Neutron Star Binaries (NSBH) and Binary Neutron Stars (BNS) in the universe. Classification of these events based on the physical properties is is essential for understanding their formation channels and other properties.The research aims to provide a computational framework/model that will aid to distinguish between BBH, NSBH and BNS events. In this research, we utilize data from the LIGO/VIRGO/KAGRA catalogue, particularly the GWTC-3 confident dataset to train a Random Forest Algorithm that can classify objects based on the data. By training on GWTC-3 data for both CSV and JSON files in Python, the model will leverage a large number of decision trees (about 150-200 trees) in order to improve accuracy. The model will especially train on the masses of compact objects from the data, where the masses are expected to be less or greater than 5 solar masses. Other parameters such as Redshift values, spin parameters (-1 or 1), probability of astrophysical origin (p-astro) will also be used to train the model to accurately predict the compact objects and classify them accordingly. The Random Forest model will be trained and tested using standard machine learning techniques. The results will include a computationally trained Machine Learning model that will classify if the gravitational wave event is a compact object binary (BBH, NSBH and BNS) or not, and percentage of accuracy on which results are displayed.

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Many galactic globular clusters (GCs) contain at least two populations of stars. Recent observational studies focused on their spatial characterisation found that the radial distributions of the first (P1) and second population (P2) of stars are vastly different in dynamically-young GCs. If we follow the conventional assumption that P2 is born more centrally concentrated, how come the populations get mixed (or even inverted) so quickly in some GCs but not others? We investigate whether some more complex dynamical processes specific to certain GCs might be at play. Our primary focus in this work is to evaluate the expansion of the P2 stars due to binary-single interactions in the core and whether they can invert the P1 and P2 radial distributions. We use direct N-body models with primordial binaries of various masses to verify this. We find that even a single massive binary star can push the central P2 outwards and fully mix P1 and P2 stars within a few relaxation times if the GC is dense enough. Consequently, we can replicate the observational properties of systems such as NGC 5053, 4590, 5904 and others.

Black hole binaries in dense stellar environments are key players in shaping the population of gravitational wave (GW) sources. Recent discoveries by LIGO/Virgo/KAGRA have shown that many black hole mergers occur in globular clusters, nuclear star clusters, and young star clusters, where their unique conditions promote hierarchical mergers—successive black hole collisions that can form exceptionally massive black holes, even reaching the pair-instability mass gap. However, the exact processes governing black hole formation, spin evolution, and long-term retention in these environments remain unclear. This study explores how black hole binaries evolve within highly dynamic stellar clusters, focusing on how gravitational wave-driven mergers and cluster escape velocities influence their fate. We analyze the effects of three-body interactions, mass segregation, and tidal hardening on merger rates and spin alignment, drawing insights from numerical simulations and the latest GW observations. Special emphasis is placed on the role of angular momentum transport mechanisms in determining black hole spin orientations, as inferred from the GWTC-3 dataset. Our findings suggest that dense star clusters serve as prime locations for second-generation black hole mergers, which has exciting implications for detecting high-spin black holes with next-generation observatories like the Einstein Telescope and LISA. By improving theoretical models and comparing them with GW data, this research contributes to our growing understanding of black hole binary evolution and its significance in the expanding field of multi-messenger astrophysics. Keywords: Black Hole Binaries, Stellar Clusters, Hierarchical Mergers, Gravitational Waves, Spin Evolution, Multi-Messenger Astronomy

Main sequence turnoffs in the color-magnitude diagrams (CMDs) of open and globular clusters alike are usually well-defined to render a determination of their ages. However, in intermediate-age star clusters within the Milky Way galaxy and the Magellanic Clouds, their main sequence turnoffs appear unusually broad, aka, ‘extended main-sequence turnoff’ (eMSTO), defying stellar evolution models of coeval single stars. Several studies have been conducted over the past decade to understand this unusual eMSTO. Stellar rotation seems to stand out among the proposed competing mechanisms to account for the eMSTO. Here, we carry out an extensive search for the eMSTO phenomenon in intermediate-age galactic open clusters. Using the ML-MOC algorithm on Gaia DR3 data, we identify members of 53 open clusters and visually examine their main sequence turnoff regions. Our observations indicate that fast and slow rotators populate redder and bluer parts of CMDs, respectively. However, higher extinctions in the direction of some clusters obscure the distinction between the positions of fast and slow rotators on their CMDs. Our analysis reveals that the eMSTO phenomena are seen in clusters of ages 0.1 – 2 Gyr. Furthermore, we find that eMSTO is more pronounced in more massive OCs. By comparing observed CMDs with rotating PARSEC stellar models, we find that while rotating stellar models can account for the presence of eMSTO in some clusters, they fall short in others.

The Interstellar Medium (ISM) is the gas and dust between the stars, which is crucial in the development of our dynamic galaxy and its star-forming processes. The star-forming nebulae M17 and W51 are in the plane of the Milky Way Galaxy (MWG). We observed M17 and W51 using the Arecibo Observatory 12-meter radio telescope to search for the Methylidyne (CH) molecule and ionized Hydrogen (H) spectral lines. These observations are part of a pilot survey of the first large-scale CH map of the galactic plane of the MWG. CH has potential to act as a significant CO-dark molecular gas tracer and better characterize low-density regions of molecular clouds. In our study, we did not detect CH in M17. In W51, however, we detected CH in the 3.3 GHz transitions. We also detected Hydrogen Radio Recombination lines (H RRLs) at 3,326.987 MHz and 3,248.707 MHz. These results are consistent with the behavior of massive star-forming regions and motivate further exploration of the state of the gas in M17 and W51.

Throughout its lifetime, a massive galaxy typically experiences multiple major merger events with other galaxies and it is well established that Supermassive Black Holes (SMBHs) are present in the centers of these vast majority of galaxies and they grow together with their central SMBHs. In the post-merger phase of galaxy evolution, the SMBHs are sinking to the new galactic nucleus by dynamical friction and may form a binary or a multiple system. The timescales of SMBH binary mergers cover a large range of 50 Myr – 1 Gyr or longer. Full cosmological simulations still cannot resolve the formation and evolution of bound SMBH systems in the galaxy merger remnants. Thus, it is important to perform high resolution N-body re-simulations to predict the outcome of these SMBH mergers and to find out the impact of the triaxial structure and of the central density profile of the host galaxies on the formation time of a hard SMBH binary in triple merger systems. It is also interesting to check what is the final outcome of SMBH triple systems and how long are the merger timescales. Earlier cosmological simulations of triple SMBH systems were performed using IllustrisTNG-100 and ROMULUS25 with very high resolution. In the first case, none of the systems formed a bound SMBH binary and they stalled at 0.1-1 kpc separation. In the second case, all three triple systems finally formed a hard binary. In this project we plan to improve the initial conditions for the triple SMBH simulations by creating triaxial initial conditions using AGAMA and apply it to ROMULUS25 simulation. Additionally, we search for potential triple SMBH merger systems in the high resolution IllustrisTNG-50 simulation with 8 times higher mass resolution in order to extend our sample. For the early evolution of the global galaxy merger phase and the decay of the SMBHs due to dynamical friction, we use the BONSAI2 tree code with ~10 million particles for each galaxy. In the later phase of hardening of the SMBH binaries by stellar encounters, we switch to the φ-GPAPE-hybrid code in order to resolve the 3- body interactions correctly. Then, we calculate the merger times and derive the expected GW signal of the merging SMBHs. Finally, we use the direct φ-GPU code for validation of critical phases, when the merger remnant still shows too much sub-structure, which cannot be properly caught by the φ-GPAPE-hybrid code. With our sample, we expect a more realistic outcome of the triple SMBH interactions and a measurement of the delay of the merger times compared to the original cosmological simulations. In conclusion, we try to investigate different dynamical properties of SMBHs binaries and multiples such as merger rates, spin evolution, and the overall outcome of the binaries or triples starting from the initial hardening phase till the final merger phase.

Close binary systems which include a massive millisecond pulsar and a low-mass companion known as spider pulsar systems, present a unique astrophysical laboratories to test fundamental physics in extreme conditions. In this study, we investigate the properties of massive pulsar J2215+5135 through the photometric observations of its companion by 3.4 m optical telescope of Iranian National Observatory (INO340). We simulate this spider system using Eclipsing Light Curve (ELC) code in order to model the impact of various radiation effects of pulsar on the companion. Through the light curve analyses, we found that the presence of a hot spot on the pulsar’s companion due to irradiation effects is essential to explain the pulse profile. As the first scientific result of INO30 after its first light, here we report the most precise mass measurement of PSR J2215+5135 to be 2.11 ± 0.0674 Msun.

ON THE EXISTENCE OF A LOCAL INTEGRALS IN THE DYNAMICS OF STELLAR SYSTEMS Fazliddin T. Shamshiev Department of Astronomy and Astrophysics, National University of Uzbekistan, Tashkent, Uzbekistan, e-mail: shamshiyev_f@nuu.uz ABSTRACT. We study the conditions under which, in addition to the energy integral, there is a local integral in stellar systems. In stellar dynamics, integrals of motion are quantities that remain constant over time and provide insight into the behavior of a system. For star systems with an arbitrary mass distribution, the integral of energy is known, or in the presence of rotation, the Jacobi integral. We investigate the possibility of the existence of an integral independent of energy, which would further limit the dynamics of the system. They demonstrate that the existence of such an integral does not impose restrictions on the shape of the gravitational potential, and is broader. This study is important for modeling the dynamics and understanding the structure and evolution of stellar systems, as it assumes that only certain types of potentials allow the existence of such local integral. The study contributes to the broader field of stellar dynamics by expanding the theoretical framework used to describe the motion of stars in galaxies and other star systems. By defining the conditions under which a local integral can exist, valuable information is provided about the stability and behavior of these systems at various gravitational potentials. The work is fundamental for astrophysicists and astronomers to understand the complex gravitational interactions within stellar systems, and may be useful for future research in this field. Subject headings: stellar dynamics — galaxies: dynamics and kinematics REFERENCES 1. F. T. Shamshiev, Journal of The Korean Astronomical Society (천문학회지), 29: S73-74, (1996), 1996JKASS.29…73S, 10.1080/1055679950820327 2. V. A. Antonov and F. T. Shamshiev, Celestial Mechanics and Dynamical Astronomy 56 (3), 451 (1993), https://doi.org/10.1007/BF00691813 3. V. A. Antonov and F. T. Shamshiev, Celestial Mechanics and Dynamical Astronomy 59 (3), 209 (1994) https://doi.org/10.1007/BF00692872 4. V. A. Antonov and F. T. Shamshiev, Astronomy Reports, Volume 38, Issue 3, May 1994, pp.426-431, 1994ARep…38..426A 5. Antonov, V. A., Shamshiev, F. T., Soviet Astronomy, Vol.36, NO. 5/SEP, P.501, 1992, 1992SvA….36..501A 6. D. Lynden-Bell, Monthly Notices Royal Astron. Soc. 458 (1), 726 (2016) https://doi.org/10.1093/mnras/stw229 7. F. T. Shamshiev, Astronomical and Astrophysical Transactions 7 (4), 269 (1995) https://doi.org/ 10.1080/10556799508203273 8. F. T. Shamshiev, in Proc. All-Russian Conf. on Astronomy at the Epoch of Multimessenger Studies, Moscow, Russia, 2021, Ed. by A. M. Cherepashchuk (Janus-K, Moscow, 2022), pp. 468–470 https://doi.org/ 10.51194/VAK2021 -2022.1.1.195 9. F. T. Shamshiev, Astrophysical Bulletin, 2024, Vol. 79, No. 1, pp. 151–158.c, 2024. 2024AstBu..79..151S, 10.1134/S1990341323600308 10. F. T. Shamshiev, Astrophysical Bulletin, 2025, Vol. 80, No. 1, (In Pleiades Publishing), Ltd., 2025.

Context : This research presents machine learning and statistical methods to identify and analyze tidal tails in open star clusters using data from the Gaia-DR3 catalog. Aims : We aim to identify member stars within five clusters—BH 164, Alessi 2, NGC 2281, NGC 2354, and M67 with ages ranging from 60 Myr to 4 Gyr—and investigate the stellar substructures for characteristics indicative of tidal tails. A detailed analysis of their morphology, population, and dynamical behavior was performed. Methods : We utilized unsupervised machine learning algorithms such as density-based clustering (DBSCAN) and principal component analysis (PCA), to analyze stars’ kinematic, photometric, and astrometric properties. Key characteristics of tidal tails, including radial velocity, color-magnitude diagram, and spatial projections in the tangent plane beyond the cluster’s Jacobi radius (r_J ) were used to detect them. Further analysis was done on the detected cluster and tail stars to study their internal dynamics and populations. The residual velocity method was also applied to detect rotational patterns in the clusters. Results : We identified tidal tails in all five clusters, with a more accurately projected span. Some of the detected tails extend farther and contain significantly more stars than previously reported. The tip-to-tip extent of the tidal tails ranges from 40 to 100 pc, containing 100 to 300 tail stars. The luminosity functions of the tails and their parent clusters are generally consistent, except in the case of NGC 2354. NGC 2281, NGC 2354 and M67 clusters and their tails showed significant rotation. Key words : open clusters and associations: individual (BH 164) – open clusters and associations: individual (Alessi 2) – open clusters and associations: individual (NGC 2281) – open clusters and associations: individual (NGC 2354) – open clusters and associations: individual (M67) – stars: astrometry, photometry, kinematics, and dynamics – methods: data analysis, machine learning and statistical

Most galaxies host supermassive black holes (SMBHs) at their centers, surrounded by dense stellar environments. Interactions between stars and the central SMBH can lead to tidal disruption events (TDEs), stellar mergers, or the ejection of hypervelocity stars. In this work, we study the statistics of stellar collisions resulting from binary star encounters with SMBHs spanning masses from 10^5 to 10^10 Msun, using a Post-Newtonian dynamical code. We find that the frequency of stellar collisions increases with black hole mass. To assess the aftermath of these events, we perform smoothed particle hydrodynamic (SPH) simulations of binary stars on parabolic orbits around a 10^9 Msun black hole. These simulations show that a small fraction of the disrupted stellar material can be captured by the black hole, potentially producing an observable signature.

Using 16 years of Fermi-LAT data and 1523 days of 3HWC survey data from HAWC, we discovered the long-sought second GeV–TeV connection towards the globular cluster (GC) UKS 1. Gamma ray spectroscopy suggests that the GeV emission can be attributed to both the pulsar magnetosphere and inverse Compton scattering (ICS) by the pulsar wind. In particular, the TeV peak is displaced from the cluster center by several tidal radii in the trailing direction of the GC’s proper motion. This alignment supports a scenario in which relativistic leptons, likely driven by a millisecond pulsar population, produce very-high-energy (VHE) gamma rays via ICS within a bow shock tail. Our findings not only highlights GCs as potential sources of VHE gamma rays, but also offers a rare opportunity to probe cosmic-ray transport in the Milky Way by studying particle propagation and anisotropic gamma-ray production associated with the extended, offset TeV feature of UKS 1.

Internal Dynamics of Omega Centauri: Towards Discrete Schwarzschild modelling

Central dense regions of the globular clusters (GCs) can contain the intermediate-mass black hole (BH) or stellar mass BH subsystem. Even at the level of the accuracy of the modern observational data for the closest GC NGC 6121, it is not possible to distinguish these two object types. We want to trace the internal kinematics and long-term orbital evolution of the stellar remnants (especially BHs) for six selected GCs. For the dynamical orbital integration of GCs, including the effects of stellar evolution, we utilise a high-order parallel N-body code φ-GPU, including external time-variating Milky Way-like potential. We perform the forward integration from 8 Gyr to present with today’s initial physical conditions (mass, half-mass radius, King concentration parameter), which give us the evolution of mass loss comparable with the current observational parameters (mass and half-mass radius) in GCs. In our simulations, we accept the Kroupa initial mass function (IMF) within the limits of 0.08-100 solar masses. For the numerical cross-checking, we performed the N-body modelling using NBODY6++ with the same initial data. The final cumulative mass profiles for the GCs indicate the dense central core, which nearly fully consists of the BHs at 8 Gyr. The binding energy for the different BH pairs shows that we have for four GCs an N-system of the bound BHs and for two GCs an N-system of the unbound BHs. As an illustration, we present the evolution of different BHs for GC NGC 6642. Based on our IMF and initial mass of 1.5 million solar masses, we have a total number of BH is around 4400. The final mass of the central BH subsystem is around 5800 solar masses. We discuss binaries evolution, as the sources of the gravitational waves during the potential merging, and the eventual formation of the IMBH in such systems.

Kilonova, the electromagnetic radiation emitted from the merger of compact binary systems, arises from intricate physical mechanisms involving processes such as r-process nucleosynthesis and interactions between heavy elements and photons via radiative transfer. Due to its complexity and rarity, comprehending the nature of kilonova proves challenging. To elucidate its characteristics, we conduct a series of simulation studies. First, we investigate how the velocity profile of the ejected material affects the resultant light curve and spectral evolution, particularly through transitions of heavy elements. Variations in the accumulation rate of these elements in the line-forming region leave distinct signatures on the kilonova light curve at specific wavelengths, leading to differential decay rates. Second, we investigate the influence of ejecta temperature and element mass on the kilonova spectrum. The strength of line features of each atom/ion in the spectrum depends on temperature and ejecta mass. As a result, the line signature of a given atom/ion is notably resonant in a specific parameter space. In this poster, I will summarize our recent findings and discuss future perspectives for understanding kilonova and its heavy elements.

Star clusters are found throughout the universe, but accurately modelling them in cosmological simulations remains a challenge due to the wide range of scales involved. One promising approach to address this is to treat star clusters as individual sink particles in zoom-in cosmological simulations, capturing their complex formation and evolution simultaneously with sub-grid models. To this end, we develop a method based on sink particles within the RAMSES code. Radiative feedback, stellar winds, and supernovae are included once star clusters form as sink particles in the simulation, regulating their growth. Subsequent internal evolution is tracked using fast cluster evolution codes which rely on local measurements of the tidal field. This allows us to model the hierarchical assembly of star clusters, the effects of clustered stellar feedback on their host galaxies, and the role of dynamical friction in disrupting massive clusters. In this talk, I will present recent results from tests of our model, including isolated GMCs and idealised galaxy simulations.

The first direct detection of gravitational waves (GWs), back in 2015, marked the beginning of a new era for the study of compact objects, and the upcoming next-generation detectors, such as Einstein Telescope (ET), are expected to add hundreds of thousands of compact binary coalescences to the list. We discovered up to 90 GW signals, from which we were able to put some constrains on the phenomenon leading to the formation, the evolution and the eventual merger of binary systems. However, the processes occurring during the evolution of such systems exhibit degeneracies, making it challenging to obtain individual constraints. In this talk, I will present our efforts to disentangle these degeneracies by performing population synthesis simulations that account for both isolated and dynamically formed black hole binaries. I will also discuss how various assumptions regarding single and binary stellar evolution affect our ability to reproduce the observed distributions from the LIGO-Virgo-KAGRA (LVK) dataset.

The remnants of gravitational wave (GW) sources offer a unique glimpse into the final stages of stellar evolution. When massive stars reach the end of their lives, they can collapse into neutron stars or black holes, often in dramatic events like core-collapse supernovae, neutron star mergers, or direct collapse. These violent processes send ripples through space-time as GWs and can also produce bright electromagnetic signals and neutrinos. Our research focuses on neutron star mergers, which not only generate strong GW signals but also lead to short gamma-ray bursts (SGRBs) and kilonovae. Another key area is black hole formation from failed supernovae—cases where a massive star collapses without producing a visible explosion, leaving only GWs and neutrinos as clues. Through multi-messenger astronomy and collaborations like the GRANDMA project, we aim to better track and understand these cosmic events. In this work, we analyze the GW signals linked to GRB 230812B and GRB 221009A, exploring what they reveal about the final moments of massive stars.

Recent advancements in artificial intelligence, particularly within the AI4Sci initiative, have paved the way for innovative computational approaches across various scientific fields, including astrophysics. This study proposes using diffusion models as a computationally efficient alternative to traditional astronomical N-body simulation. While conventional N-body methods are critical for modeling gravitational interactions, they often come with high computational costs. In contrast, our data-driven strategy aims to capture the underlying physics mechanism of stellar groups with significantly reduced computational overhead and generate datasets where needed. By integrating diffusion models into astrophysical simulations, this proposed work highlights the transformative potential of AI, enhancing both the scalability and accessibility of simulation tools in computational astrophysics.

Omega Centauri (ω Cen) is the most massive globular cluster in the Milky Way and is suspected to be the remnant nuclear star cluster of an accreted dwarf galaxy. The binary population of ω Cen is of particular interest since binary systems play a key role in the cluster’s dynamical evolution and stellar interactions. In addition, binary black hole systems could provide direct evidence for the as yet undetected population of thousands of stellar mass black holes expected to live in the cluster. We present a systematic search for binary systems in ω Cen using high precision astrometric data, expanding on recent radial velocity and proper motion studies (Wragg et al. 2024, Platais et al. 2024, Saracino et al. 2025) that have revealed more long period binaries than expected from theory. Our dataset includes >500 individual Hubble Space Telescope observations taken over 20+ years, most taken as part of calibration programs. We show these observations are sensitive to long-period binaries, with black hole binaries detectable at periods longer than ~100 days. We find a population of >100 previously undetected potential binaries based on correlated excess astrometric noise, and present orbital fits to some of the most promising binary candidates.

This poster examines Ultraluminous X-ray sources (ULXs) in globular clusters (GCs) using MOCCA code simulations. Our results show that non-tidally filling clusters host significantly larger ULX populations than tidally filling ones, as tidal stripping inhibits progenitor formation. ULXs are more common in younger clusters (≲300 Myr), explaining their relative scarcity in observed GCs compared to field environments. Notably, Intermediate-Mass Black Hole ULXs (accretors >500 M⊙) occur exclusively in non-tidally filling simulations with multiple stellar populations, comprising 16–44% of ULXs when present. A key discovery is the identification of “escaper” ULXs—systems dynamically ejected from GCs while still emitting X-rays—constituting one-seventh of all simulated ULXs. For neutron star (NS) accretors, escapers are twice as common as in-cluster counterparts, with NS accretors representing 40% of escapers versus only 4% of in-cluster ULXs. These escapers typically have lower component masses and tighter orbits, suggesting they may significantly contribute to the observed field ULX population. These findings underscore how GC dynamics profoundly influence ULX formation and distribution both within clusters and in field environments.

Open star clusters are vulnerable to continuing disintegration. Upon emergence from the molecular clouds after star formation, two-body relaxation among member stars leads to the ejection of the least-massive members, ever shallowing the gravitational potential. External tidal forces in the Galactic disk exacerbate the situation making the open clusters with hundreds to thousands of members we witness today merely survivors. Disintegrating star clusters leave behind traces as tidal tails. While the majority of stars are in double or multiple systems, and pair galaxies are common, double star clusters are relatively rare. In this project, we aim to study the formation and survival of the double star cluster, ℎ and 𝜒 Persei by diagnosis of the morphological substructures, i.e., stellar groups that share the same distance and space motion but distinctly surround the cluster pair. Using the astrometry and photometry from the latest space mission Gaia (Data Release 3), we have tentatively identified more than a handful of such groups surrounding ℎ and χ Persei, some detected for the first time. We intend to probe a much larger field than in the literature to find stellar debris not known before. With a reliable membership for each group, the parameters such as the linear size, number of stars, distance, age, and chemical composition, will be derived. More importantly, from the relative motion of these debris groups, we will delineate their kinematic relation with the paired cluster — whether some were leftover groups from the binary cluster formation, or were thrown out as the pair orbit each other.