“From Nbody1 to Nbody6 : The Growth of an Industry” is the title of a 1999 invited review by Sverre Aarseth, for Publications of the Astronomical Society of the Pacific (PASP). I took this as an inspiration for the title of this paper; it describes how Sverre’s Nbody Industry has further grown since 90s of the previous century, and how it is further flourishing and hopefully developing, in his spirit, even after the sad news of his passing away reached us. My contact and friendship with Sverre started a few decades ago being sent to Cambridge to learn Nbody5, counting input parameters, and learning about the fact that even a sophisticated code (which had already at that time quite a history) requires permanent maintenance and bug fixes. Managed by Sverre, who relentlessly ran his code and responded to the widely spread crowd of “customer” colleagues. There has been a phase of massive and fast development and improvements due to vectorization, parallelization, GRAPE and GPU acceleration, and Sverre has been always on top of it if not ahead, but also fully adopting ideas of collaborators, once they tested well. Nbody6++GPU and Nbody7 entered the scene, and also recent new competitors, such as PeTar or BiFrost. We all have learnt a lot from Sverre, and strive to continue in his open-minded spirit, for open source and exchange. A striking evidence for the further growth of the “industry” is the number of papers here (and two of them follow in this session, but also in other sessions) using and further developing the aforementioned codes, as well as the occurrence of new and competing codes, which keep the field alive.

Understanding the origin of hypervelocity stars (HVSs) in the Galactic Center is a critical question, particularly regarding the dynamic processes that have shaped this region. In this study, we assert that HVSs likely formed as counterparts to S stars, specifically through the Hills mechanism originating in the young stellar disk. By employing N-body simulations, we thoroughly analyze the statistical likelihood of HVS production in our models and robustly compare these results with observational data of a recently detected HVS, S5-HVS1, with an origin in the Galactic Center. Our findings provide a consistent model that enables the production of HVSs like S5-HVS1 and captures the known dynamics of the Galactic Center.

Intermediate-mass black holes (IMBHs) occupy the $10^2$–$10^5\,M_\odot$ range, but their existence remains poorly constrained. Only a few candidates have been suggested in dwarf galaxies, globular clusters, and LIGO-Virgo-Kagra detections. To investigate their formation and demographics, we adopt two complementary approaches. We first analyze the dragonii direct N-body simulations, which follow clusters with up to $10^6$ stars, capture IMBHs growth. We then employ the semi-analytic code bpop, calibrated on dragonii, to explore a broad range of cluster and cosmological conditions.

Our models reproduce merger rates consistent with GWTC-3, with $\sim30$–60% of BBHs forming dynamically, mainly in globular and nuclear clusters. About 2–3% of mergers involve an IMBH, producing intermediate-mass ratio inspirals. The IMBH mass distribution spans $2.5\times10^2$–$4\times10^4\,M_\odot$, with rare growth beyond $10^6\,M_\odot$. Formation efficiency rises with initial binary fraction but declines in metal-rich environments. IMBHs thus emerge as a distinct population bridging stellar and supermassive black holes.

Star clusters are born immersed in molecular gas and hidden by huge extinction. Their evolution is determined by how the young stars interact with the gas and especially on the efficiency with which the gas is turned into stars. The high pressure of starburst regions encourages cloud collapse and cluster formation; the most massive proto-clusters forming in the Local Universe are over-pressured by accreting molecular filaments. Stellar winds can combine to form cluster super-winds that clear away the gas (negative feedback) or that stall inside the cluster to create a second generation of stars from enriched material (positive feedback). We review recent observations and models of young clusters in the embedded and emerging stages.

We investigate the variation in the upper end of stellar initial mass function (uIMF) in unresolved, compact and young stellar clusters (YSCs) in five nearby galaxies within 5 Mpc. All the YSCs in the sample are younger than 4 Myr and have masses above 500 M⊙. The YSC catalogs, produced from the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program, are used to measure the YSCs’ Hα luminosity as a proxy for their ionizing photon rate and chart its trend as a function of the cluster’s stellar mass (Mcl). We carefully account for stochastic sampling of the uIMF by selecting the samples independently of the presence of Hα emission, thus removing a potential sample bias. We find that the uIMFs show no dependence on Mcl, suggesting that the maximum stellar mass (mmax) produced in star clusters is universal, in agreement with previous findings.

We have proposed that the W1 kilomaser, associated with a super star cluster in the starburst galaxy NGC 253 could arise in an accretion disc around a supermassive star (SMS) with a mass of around 4000 M⊙. Those hypothetical stars have been proposed as polluters responsible for chemical peculiarities in globular clusters.

Stellar evolution studies of low-to-intermediate mass stars are hindered by the lack of a solid link that connects their initial and final properties. This problem can be resolved for stars that are members of star clusters and at the final stages of their evolution. In such cases, we can estimate their final properties from direct measurements and obtain the necessary information for the properties of their progenitors from independent cluster studies. Here, we focus on the study of planetary nebulae that are confirmed members of Galactic open star clusters. These rare instances provide us with a new additional sample of data, which contributes to the fundamental initial-to-final mass relation (IFMR). We examine the quality of this contribution and assess the efficacy of our method, showing that our approach is very promising with already significant initial results. Our data generally confirm the latest IFMR trends, filling important gaps in the process.

Determination of membership of star clusters is a very important criterion in their study as they effect determination of cluster parameters like radius, age, distance, mass functions, etc. In an earlier study, we used published membership data of nine open star clusters as a training set to find new members from Gaia DR2 data using a supervised Random Forest (RF) model with a precision of around 90%. The number of new members found was almost double the published number. In this work, we would like to compare the earlier results with results obtained by applying the unsupervised method of Gaussian Mixture Modelling (GMM) and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) to study the membership of open star clusters of varying ages and locations in the Galaxy using Gaia DR2 and EDR3 data. We shall discuss these techniques and focus on the caveats involved.

Determination of membership of star clusters is a very important criterion in their study as they effect determination of cluster parameters like radius, age, distance, mass functions, etc. In this paper, we apply the unsupervised method of Gaussian Mixture Modelling (GMM) to find membership of 9 open star clusters of varying ages and locations in the galaxy using Gaia DR3 data. We compare our results to help understand the efficiency of GMM. We find that this method works well with relaxed clusters with ages larger than their relaxation times they approximate Gaussians better.

Supermassive stars have been proposed as the solution to a number of longstanding problems in globular cluster formation. The hypothetical stars have been suggested as potential polluters responsible for the observed chemical peculiarities within those clusters. In recent hydrodynamic simulations, we have demonstrated that accretion discs around such stars are stable even with large stellar accretion and flyby rates and produce H2O kilomasers. We propose that the W1 kilomaser, associated with a super star cluster in the starburst galaxy NGC 253, may arise in an accretion disc around a supermassive star with a mass of around 4000 Mʘ.

We have made a lot of progress in the study of the MW. In spite of this, much of our Galaxy remains unknown, and amazing breakthroughs await to be made in the exploration of the far side of the Galaxy. Focussing on the Galactic extinction horizon problem with current surveys like the Two Micron All-Sky Survey (2MASS) and the Vista Variables in the Via Lactea Survey (VVV) and its extension VVVX, the extinction horizon is a fundamental difficulty, and it is my intention here to reveal how profound is our ignorance, and also to try to suggest ways for improvement with future near-IR Galactic surveys.

. We present a significantly improved version of our numerical code JASMINE, that can now solve the Jeans equations for axisymmetric models of stellar systems, composed of an arbitrary number of stellar populations, a Dark Matter halo, and a central Black Hole. The stellar components can have different structural (density profile, flattening, mass, scale length), dynamical (rotational support, velocity dispersion anisotropy), and population (age, metallicity, Initial Mass Function, mass-to-light ratio) properties. These models, when combined with observations, will allow to investigate important issues, such as quantifying the systematic effects of IMF variations, of mass-to-light ratio gradients, and of different stellar kinematic components (e.g. counter rotating disks, kinematically decoupled cores) on luminosity-weighted properties. The developed analytical and numerical framework aims at modeling Early-Type Galaxies, but it can also be applied to dwarf Spheroidal galaxies and Globular Clusters.

We present a scenario for the formation of super star clusters (with masses larger than 105 M⊙) in which multiple generations of star formation will occur. We stress that the gas left over (∼50%) from first generation (1G) star formation should be retained in such massive clusters (thanks to their deep potential wells, with escape speeds larger than 10 km/s) and be available for a second or even third generation of stars, with the basic HeCNONaMgAl chemical anomalies observed in globular clusters, the latter assumed to be the descendents of these super star clusters. One new feature of this model is the role of C+ cooling of the dense warm trapped neutral or ionized gas which defines a characteristic temperature of ∼100 K, leading to a second generation (2G) of stars with a top-heavy IMF (M > 5 M⊙). The ashes of the 2G very massive stars (VMS, M > 100 M⊙) sampled in this IMF quickly pollute and dilute the left-over pristine gas with their slow winds (that cannot escape the cluster), while the majority of massive stars develop fast winds (that actually can escape from the cluster). Meanwhile, much of the remaining dense T = 100 K gas contracts gravitationally in the massive cluster and may reach densities of the order of 109 cm−3, in which case the Jeans mass drops to about 0.2 M⊙ and leads to a substantial low-mass pre-MS 3G population (most likely on a very short timescale). In this way, we may solve both the mass budget and the excess Helium problem in proto-globular clusters, while also explaining the Na-O and Mg-Al anti-correlations resulting from hot H-burning of very massive stars at 45MK and 75MK, respectively.

The origin of the chemical anomalies in star clusters is still an open question, although much effort has been employed both from a theoretical and observational point of view. The exploration of the dependence of such multiple stellar populations based on certain cluster properties (e.g. mass, age, metallicity) has represented a compelling line of investigation so far. Here I report an overview of the results obtained from our latest surveys aimed at characterising the phenomenon of chemical variations in star clusters that are much younger with respect to the ancient globular clusters. The fundamental question we are asking is whether these abundance patterns are only restricted to the old massive clusters; and if not, is there a difference between young and old objects?

Several observational and theoretical studies suggest that the initial mass function (IMF) slope for massive stars in globular clusters (GCs) depends on the initial cloud density and metallicity, such that the IMF becomes increasingly top-heavy with decreasing metallicity and increasing the gas density of the forming object. Using N-body simulations of GCs starting with a top-heavy IMF and undergo early gas expulsion within a Milky Way-like potential, we show how such a cluster would evolve. By varying the degree of top-heaviness, we calculate the dissolution time and the minimum cluster mass needed for the cluster to survive after 12 Gyr of evolution.

A vast number of observed galactic nuclei are known to harbour a central supermassive black hole (SMBH). In their early lifetime, these systems might have witnessed the strong interaction between the SMBH and massive star clusters formed in the inner galactic regions. Due to the strong tidal field exerted from the SMBH, clusters are likely to undergo tidal disruption, releasing their stars all around the SMBH, and possibly driving the formation of a nuclear cluster (NC). This mechanism can contribute to populate galactic nuclei with intermediate-mass black holes (IMBH). Interactions with the central SMBH can lead to the formation of tight massive BH binaries (MBBH) that undergo coalescence via gravitational waves (GW) emission. We discuss this mechanism in the context of the Milky Way centre, exploring the possibility that SgrA*, the Galactic SMBH, has an IMBH companion.

The identification of young massive star clusters (YMCs) at high redshift is becoming a real fact. We present recent results from Hubble deep imaging and VLT/ MUSE - X-Shooter observations boosted by strong gravitational lensing. We report on two parsec-scale star-forming systems at z = 6.145 and 2.37 (>10 Gyrs of look back time) currently representing the best candidate high-z YMCs. All of this also implies that the search for globular cluster precursors has already begun.

An outline is given of the main research programs currently in progress at the Carter Observatory. These include: the establishment of a set of standard star magnitudes and colours in the Vilnius seven-colour photometric system; the study of galactic and extragalactic star clusters using Vilnius and broadband photometries; binary stars and the development of APTs; and the history of Australasian astronomy. The role of Carter Observatory Honorary Research Associates is described and mention is made of the joint New Zealand/Japan program to observe gravitational microlensing effects, discover variable stars and patrol selected clusters of galaxies for supernovae.

The stellar content of young massive star clusters emit large amounts of Lyman continuum photons and inject momentum into the inter stellar medium (ISM) by the strong stellar winds of the most massive stars in the cluster. When the most massive stars explode as supernovae, large amounts of mechanical energy are injected in the ISM. A detailed study of the ISM around these massive cluster provides insights on the effect of cluster feedback.

We present high quality integral field spectroscopy taken with VLT/MUSE of two starburst galaxies: ESO 338-IG04 and Haro 11. Both galaxies contain a significant number of super star clusters. The MUSE data provide us with an unprecedented view of the state and kinematics of the ionized gas in the galaxy allowing us to study the effect of stellar feedback on small and large spatial scales. We present our recent results on studying the ISM state of these two galaxies. The data of both galaxies show that the mechanical and ionization feedback of the super star clusters in the galaxy modify the state and kinematics of the ISM substancially by creating highly ionized bubbles around the cluster, making the central part of the galaxy highly ionized. This shows that the HII regions around the individual clusters are density bounded, allowing the ionizing photons to escape and ionize the ISM further out.

The Herschel/HOBYS key program allows to statistically study the formation of 10−20 M ⊙ stars. The IRAM/W43-HERO large program is itself dedicated to the much more extreme W43 molecular complex, which forms stars up to 50 M ⊙. Both reveal high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. Given their activity, these so-called mini-starburst cloud ridges could be seen as “miniature and instant models” of starburst galaxies. Both surveys also strongly suggest that high-mass prestellar cores do not exist, in agreement with the dynamical formation of cloud ridges. The HOBYS and W43 surveys are necessary steps towards Galaxy-wide studies of high-mass star formation.