Star clusters do not form in isolation, but enshrouded in hierarchical gaseous filaments embedded in a galactic tidal field. To understand the role of radiation, stellar winds and supernovae of massive stars in regulating the multiphase interstellar medium we must decipher how the young host clusters form, evolve and interact with their surrounding galactic environment. In this talk, I present...
The GigaEris simulation is a cosmological, N-body hydrodynamical "zoom-in" simulation of the formation of a Milky Way-sized galaxy with the unprecedented resolution of better than a thousand solar masses, encompassing of order a billion particles within the refined region. The simulation employs a modern implementation of smoothed-particle hydrodynamics, including metal-line cooling and...
Stars will typically spend the first few million years of their lives in their natal star-forming regions. The initial densities in these regions often mean young stars are much more likely to experience the effects of close encounters, massive star stellar winds and potentially even nearby supernovae. Therefore, understanding the dynamical evolution of star-forming regions is key to...
To understand the impact of radiation feedback during the formation of a globular cluster (GC), we simulate a head-on collision of two turbulent giant molecular clouds (GMCs). A series of idealized radiation-hydrodynamic simulations is performed, with and without stellar radiation or Type II supernovae. We find that a gravitationally bound, compact star cluster of mass $M_{GC} \sim 10^5...
The formation of multiple populations of stars in globular clusters and their further evolution is still the subject of much debate and awaiting resolution. Many scenarios have been proposed to explain their formation. One of the most commonly proposed is the AGB scenario, in which chemically reprocessed gas from the envelopes of AGB stars mixes back with primary gas flowing into the center of...
Globular clusters (GCs) are among the most fascinating objects in the Universe, but their formation and evolution remain a key challenge in astrophysics. These dense and compact agglomerates of stars are believed to have formed from the dense cores of super-giant molecular clouds during the earliest stages of galaxy formation. However, the environment in which GCs originated is still quite...
Star clusters (SCs) are not born in spherical symmetry, contrary to the idealized initial conditions used in the vast majority of $N$-body simulations performed so far. Observations suggest that the initial conditions for star formation are highly structured and clumpy, both in the distribution of molecular gas from which stars form (Williams 1999 and references therein) and in the...
Initial conditions of stellar cluster simulations generally consist of a monolithic structure. However, both theoretical and observational studies suggest that stellar clusters form hierarchically and therefore host subclusters that could trigger stronger stellar interactions. Hence, it is fundamental to include more detailed initial conditions when studying the evolution of stellar clusters...
We have proposed a formation scenario for dSph galaxies which does not include any interaction with other galaxies, called the Dissolving Star Cluster Model. In this model the gas, accumulating inside the dark matter halo of the dwarf forms stars in form of small star clusters and associations which orbit the central region of the dark matter halo. These small entities do not survive for...
According to the standard LCDM model, the globular clusters (GCs) of the Milky Way (MW) are the first gravitationally bound stellar systems to form in the early Universe, with a typical age of about 10-12 billion years. GCs are quite common in the Galaxy. In early 2020, 150 of them were found in the MW, in 2022 - 160, and more than 10 stellar systems are candidates for GCs. In the past few...
The Galactic center region has a mass of ~10^9 M_sun. It consists of the nuclear stellar disk (NSD), a flat, rotating stellar structure, and the nuclear star cluster (NSC), the densest concentration of stars in the Galaxy.
The NSC and NSD are distinct structures of the Milky Way, but also connected to the larger Milky Way structures, e.g. via the inflow and outflow of gas, and the infall of...
The nuclear star cluster (NSC) of the Milky Way has been extensively studied in the last decades, using ground-based astrometry and spectroscopy of ~10000 stars in the inner 10 pc.
The Galactic centre is unique in that we have a direct measurement of the mass of the supermassive black hole (SMBH) from the motion of S-stars, which can be tracked for a significant fraction of the orbital...
Since 2017, the GRAVITY interferometer at ESO's Very Large Telescope has allowed us to obtain astrometric data with unprecedented accuracy of the S-stars orbiting around Sagittarius A*, turning them into a powerful tool to investigate the gravitational potential around the supermassive black hole at the center of our Galaxy.
In particular, for the star S2, we have been able to detect the...
Recently the precession rate of S2 around the SMBH at the Galactic Center is reported (Abuter et al., 2020). At the same time, other astronomical and physical values, such as orbital elements of S2, mass of the central SMBH, the distance to it, parameters for GR effect and so on, are estimated.
From a theoretical point of view, Rauch & Tremaine (1996) predicted the precession of stars...
Galactic nuclei, the densest stellar environments in the Universe, exhibit a complex geometrical structure. The stars orbiting the central supermassive black hole follow a mass segregated distribution both in the radial distance from the center and in the inclination angle of the orbital planes. This distribution may represent the equilibrium state of vector resonant relaxation (VRR).
In...
Star systems containing three stars are common in the universe, with the triple fraction increasing with the mass of the star. Approximately 10% of solar-type stars reside in triples, while this fraction goes up to 60% for 10 stars of 10 solar masses. To fully understand the evolution of massive stars, triple evolution should be taken into account. One of the evolutionary pathways for triples...
Star clusters are ideal test beds for studying the formation and evolution of stars in diverse environments. Open clusters, being relatively sparse systems and located at a closer distance, as compared to the globular clusters, allow a more detailed analysis of their individual single and multiple stellar members. Trumpler 5 is a populous, intermediate-age (~3.4 Gyr), metal-poor ([Fe/H] ~...
We report the discovery of four blue lurkers with low- and extremely low-mass white dwarf (ELM WDs) companions in the Galactic globular cluster NGC 362 using AstroSat’s Ultra Violet Imaging Telescope (UVIT). We analyzed the multi-wavelength spectral energy distribution (SED) of FUV-bright MS stars using data from the UVIT, UVOT, GAIA EDR3, and 2.2m ESO/MPI telescopes. Two each of low-mass WDs...
Recent studies have shown, that inconsistencies in the integrated colour indices (CIs) between real star clusters and theoretical models arise due to projection of bright stars inside the apertures. Thus, in this study we determined achievable accuracy and applicability limits of the aperture photometry approach for star cluster studies. We modelled a large grid of artificial 3D star clusters...
It is well established that the frequent stellar dynamical interactions in the high-density globular cluster (GC) cores make them efficient factories of exotic objects, including millisecond pulsars (MSPs). In fact, the number of MSPs per unit mass in the Galactic GC population is some $10^3$ times larger than in the Galactic field.
As part of a large project that aims at exploiting the...
We quantify for the first time the gravitational wave (GW) phase shift appearing in the waveform
of eccentric binary black hole (BBH) mergers formed dynamically in three-body systems. For this,
we have developed a novel numerical method where we construct a reference binary, by evolving the
post-Newtonian (PN ) evolution equations backwards from a point near merger without the inclusion
of...
Using MUSE spectroscopy, we have recently revealed the existence of distinct populations of slowly and fast rotating stars in young (<2 Gyr) massive (10^5 solar masses) star clusters in the Magellanic Clouds. The differences in the stellar angular momenta naturally explain peculiar features observed in the colour-magnitude diagrams of the clusters, such as split main sequences or extended...
Star clusters play a pivotal role in understanding galaxy formation processes and evolution. However, investigations of star clusters within the disk of our Galaxy are limited due to interstellar extinction. Therefore, to understand evolution of star cluster systems in galaxy disks observations of nearby galaxies are needed. The best object for this purpose is the Andromeda (M31) galaxy, where...
Population III (Pop III) stars are ideal candidates for the formation of intermediate-mass black holes (IMBHs) because of their small mass loss and top-heavy initial mass function. If such stars were to form in star clusters, their IMBH remnants would have a higher probability of creating binary systems and eventually merge, leaving behind black holes (BHs) massive enough to be seeds of the...
To date, several planetary systems around pulsars are known. While those systems could be relics, another formation channel has recently been proposed. Massive stellar remnants (i.e., neutron stars and black holes) likely receive a natal supernova velocity kick due to the asymmetry of their birth event, propelling them through space at high speed. We study the hypothetical encounters between...
Stellar-mass black holes play a crucial role in the dynamical evolution of globular clusters. In this work we discuss a fast method to evolve star clusters with varying initial black hole contents. We use the fast model clusterBH to reproduce the evolution of globular clusters in the database of Cluster Monte Carlo (CMC) models. In particular, we reproduce the evolution of the total stellar...
Binary black hole inspirals in globular clusters occur when the binary's eccentricity surpasses a critical value, denoted as $e_{\rm GW}$. This $e_{\rm GW}$ depends mainly on the binary's masses and semi-major axis. We perform $10^7$ binary-single scattering experiments with unequal masses to identify the different channels that produce high eccentricity binaries. We determine how the cross...
Blue straggler stars (BSS) are rejuvenated core hydrogen-burning stars that are bluer and brighter than the main-sequence turnoff stars of star clusters. They are believed to have formed via binary evolution and multiple stellar interactions. BSS are among the most massive populations of star clusters and therefore experience significant gravitational drag compared to other cluster populations...
We investigated the available Gaia catalogue data (DR3) of open clusters and studied cluster distances, sizes and membership distributions in the 3D space. The dependence of distance and size on the parallax-to-distance transformation was analysed. We argue that within two kpcs, the inverse-parallax method gives results comparable to the Bayesian approach based on the exponentially decreasing...
The Hubble constant is a crucial cosmological parameter that is a measure of the rate of change of the cosmic scale factor per unit cosmic scale factor i.e. a_dot / a. There is a considerable discrepancy between the measurements of the Hubble constant from standard candle observations and those from cosmic microwave background (CMB) observations. Data from gravitational wave (GW) events can...
Gravitational Waves have proven to be an excellent tool for understanding populations of binaries. In this work, we investigate the population of White Dwarf binaries in the Milky Way. We calculate the Gravitational Wave background from these sources in the LISA sensitivity range.
We use the COMPAS population synthesis code, and investigate the dependence of the background spectrum on the ...
Most massive stars form in binary or even multiple systems. During their evolution, these binaries almost inevitably undergo a critical phase where the binary members exchange mass. It has been shown that this mass transfer plays a crucial role in shaping the evolution of both stars and is responsible for many fascinating astrophysical phenomena currently being observed, such as the formation...
During the early dynamical evolution of a dense stellar system, such as a young star-forming region, stars can be ejected as runaway stars following a close dynamical interaction. These stars are still extremely young at the time of ejection and might harbour a protoplanetary disc, which has been truncated or limited in size by the ejection encounter. Based on three runaway stars from the...
In this work, we present an understanding of the complex mechanisms that govern the evolution of orbits in the Galactic Centre. Through N-body simulations, we have gained crucial insights into the evolution of disk-like structures in the Galactic Centre. We see that post-Newtonian corrections and perturbative effects are critical in stabilizing these structures. In their absence, these...
Introduction: The gravitational encounters occurring in Globular Clusters (GCs) drive the system toward energy equipartition and trigger other dynamical processes, that still require a self-consistent theoretical description. Internal kinematics observations show a partial degree of equipartition (Libralato et al. 2018, 2019, 2022; Watkins et al. 2022), confirming N-body predictions...
Globular clusters (GCs) can be used to probe the Milky Way's accretion history, potential, and dark substructures. Additionally, GCs could provide formation pathways for nuclear star clusters and supermassive black hole seeds. A detailed understanding of GC formation and evolution is therefore necessary, so it is important to capture the relevant physics in cosmological simulations. Several...
The presence of young stellar populations in Large Magellanic Cloud cluster NGC 1783 has caught significant attention, with suggestions ranging from it being a genuine secondary stellar generation to a population of blue straggler stars or simply contamination from background stars. Thanks to multi-epoch observations with the Hubble Space Telescope, proper motions for stars within the field...
Clustered star formation is the dominant mode of star formation across cosmic time. Moreover, it plays a key role in many fundamental areas of astrophysics: from the early interplay between stellar and gas dynamics to the formation of gravitational wave sources and exotica, from the dynamical properties of young star clusters to galaxy assembly and evolution. Yet, the underlying physical...
An intriguing phenomenon in globular clusters is the presence of multiple stellar populations with different light element compositions. The origin of this phenomenon is still unclear, but a key piece of information to solve this enigma resides in the structural and kinematic differences of the stellar populations. Globular clusters are, in general, very old stellar populations, but...
Galactic globular clusters (GGCs) are known to have some degree of chemical complexity, indicating that they do not consist of a "single" stellar population. Instead, some stars have an atmospheric composition showing evidence of material processed by nuclear reactions. Recently, the issue has also been raised about how "mono-metallic" GGCs are. Intrinsic Fe dispersions among RGB stars of GGCs...
Dense stellar systems, such as globular clusters and nuclear star clusters, represent natural laboratories for exploring the intricate interplay between gravitational interactions, stellar dynamics, and the formation of exotic objects like intermediate-mass black holes (IMBHs). Recent discoveries of massive black holes above 10^7 Msol in stripped nuclei within the Virgo and Fornax clusters...
Globular clusters (GCs) are among the most ancient objects in the local Universe, acting as tracers of galaxy formation across both space and time. With the recent JWST discovery of nitrogen-rich star formation in a redshift 11 galaxy, and the discovery that over 50% of the in-situ stars in the Milky Way (MW) likely formed in clusters, understanding the role of GCs in the context of galaxy...
Binary systems are important constituents of massive star clusters. They have been invoked to play an important role in the origin of phenomena observed in these environments, such as the extended main-sequence turn-offs, and to lead to the formation of exotic objects (blue straggler stars, low-mass X-ray binaries, Be stars etc).
A detailed characterization of the orbital properties of...
Empirical constraints on the internal dynamics of open clusters are important for understanding their evolution and evaporation. High precision astrometry from Gaia DR3 are thus useful to observe aspects of the cluster dynamics. This work aims to identify dynamically peculiar clusters such as spinning and expanding clusters. We also quantify the spin frequency and expansion rate and compare...
N-Body simulations are adopted to understand the rotation in star clusters via the code N-Body6++GPU. The morphology of open clusters are significantly changed due to bulk rotation, especially at the early a few dozen million years. Binary systems also plays an important role in the dynamical evolution of rotating clusters. By comparing simulations to observation, we provide an example of a...
One of the most important quantities needed for understanding a stellar cluster’s (SC’s) formation and evolution is it’s stellar mass and mass function (MF). However, the measurements of these quantities are complicated by the possible presence of unresolved binaries. This contribution explores the influence of unresolved binaries on the measured SC mass and MF. It also investigates the impact...
The majority of Milky Way globular clusters (GCs) display a small, yet significant, amount of angular momentum, clearly detectable from line-of-sight and proper motion data sets. The origin of this angular momentum is still unknown, but its emergence may be linked to the primordial formation of GCs in the high-redshift universe.
In this talk, I will present 2 sets of direct N-body simulations...
Massive stars have a significant impact on the dynamical evolution of star clusters. They play a crucial role during star formation, as their radiation can push surrounding gas away and inhibit further star formation. Additionally, strong mass loss from massive stars via strong winds can rapidly reduce the gravitational potential of star clusters and trigger their fast expansion. Once these...
Each outcome of the four-body problem can be regarded as some variation of the three-body problem. For example, when two single stars are produced (the 2 + 1 + 1 outcome), each ejection event is modeled as its own three-body interaction by assuming that the ejections are well separated in time. For each outcome, we derive, using the density-of-states formalism, analytical distribution...
The 3-body problem poses a longstanding challenge in physics and celestial mechanics. Despite the impossibility of obtaining general analytical solutions, statistical theories have been developed based on the ergodic principle. This assumption is justified by chaos, which is expected to fully mix the accessible phase space of the 3-body problem.
We probed the presence of regular (i.e. non...
Recent observations with HST and Gaia deepened our understanding of the internal kinematics of star clusters. Motivated by those findings, we aim to gain theoretical insights into how various kinematic properties influence the overall dynamical development of these stellar systems. Through N-body simulations, we explore the effects of different initial velocity distributions, ranging from...
AMUSE, the Astrophysical Multipurpose Software Environment, has been around since 2009, and it has been used in many different projects. AMUSE offers users the ability to combine different specialised simulation codes in a single simulation, which makes it possible to simulate complex systems that require interaction between different physical aspects and/or scales. Topics AMUSE has been used...
Globular clusters (GCs) have multiple populations identified through abundance variations in a number of light elements. These populations also show, in some cases, differences in some dynamical properties such as their concentration, systemic rotation, and velocity anisotropy, differences that might still preserve partial memory of the initial configuration of the stellar populations. In this...
I will discuss how gas affects the evolution of multiple star systems in young star clusters and other gas-rich environments. In particular, gas can shrink and circularize wide binaries, potentially explaining observed changes in binary properties with star cluster age. Additionally, gas can trigger instabilities in multiple systems. Finally, gas may trigger the formation of binaries and...
The dynamical evolution of planet-like objects in star clusters is not easy observable in star clusters, and it still not possible in dense star clusters such as globular clusters. I will first introduce previous works that looked into the motion of these objects, and then I will numerically explore the dynamical evolution of such objects, varying the number density of the hosting star...
Our recent investigation (Ishchenko et al. 2023) was found the 10 Milky Way globular clusters which can potentially to interact with the nuclear star cluster during their lifetime. For the dynamical orbital integration of GCs, including the effects of stellar evolution, we employed a high-order parallel N-body code φ−GPU, which is based on the fourth-order Hermite integration scheme with...
We present the results of a set of N-body simulations aimed at investigating the long-term kinematic and spatial evolution of rotating multiple-stellar populations in globular clusters.
Our simulations start with a compact, rapidly rotating, and flattened second-generation (SG) subsystem embedded in the central regions of a more diffuse, and slow rotating first-generation (FG) cluster.
We...
Globular clusters (GCs) are among the longest-studied stellar systems. Despite extensive study, their formation mechanisms, evolutionary history, and interplay with the host galaxy are still unknown. A key to solving these questions lies in the analysis of their internal kinematics, which can provide invaluable insights into their dynamical evolution. However, the study of GC kinematics...
The formation process of star clusters has not been fully understood yet. Recent numerical simulations of star-cluster formation are reaching the mass of globular clusters (1e6 Msun). However, in hydrodynamics simulation with N-body, the stars have been treated as super particles, representing several stars as one particle. We have developed a new N-body/smoothed-particle hydrodynamics (SPH)...
Despite the rising number of binary black hole (BH) mergers detected as gravitational wave (GW) sources by LIGO/Virgo, the evolutionary origin of these events remains a mystery. A growing body of evidence suggests that many of these events originated in dense stellar environments like globular clusters (GCs). Dense environments can produce qualitatively different properties of binary BH...
The LIGO/Virgo detections showed unexpected progenitor black hole masses (~66 solar mass). Such black holes with their mass falling in the pair instability mass-gap region seek a new formation channel. We focus on the so-called AGN channel to understand such a puzzling progenitor mass. In this study, we numerically model 3D global MHD accretion flows of embedded black holes within a turbulent...
Observations and high-resolution hydrodynamical simulations indicate that massive star clusters assemble hierarchically from sub-clusters with a universal power-law cluster mass function. We study the consequences of such assembly for the formation of intermediate-mass black holes (IMBHs) at low metallicities ($Z=0.01\;Z_\mathrm{\odot}$) with our updated N-body code BIFROST based on the...
Gravitational wave detections of black holes (BHs) in the pair-instability mass gap have sparked interest in dynamical formation channels. In my work, I have explored the process of hierarchical BH mergers in active galactic nuclei (AGNs), which stand out with respect to other dynamical environments for three main reasons: enhanced binary formation due to migration traps, accelerated binary...
I first quickly review the decades-long history of the development of the methods for simulating the dynamical evolution of star clusters, with additional discussion of N-body methods. Then I survey some things that can or could go wrong, with particular attention to the role played by the theory of two-body relaxation.
Dwarf Spheroidal galaxies and Ultra Faint Dwarf galaxies orbiting around the Milky Way are commonly considered as dynamically "hot" systems so that the high velocity dispersions measured could be compatible with a virial state just if their total mass is very large respect to the luminous mass. This led to the consideration that they are the most dark matter (DM) dominated stellar systems in...
As a graduate student I had the privilege to learn from Daiichiro Sugimoto (then Visiting Gauss professor at Uni Goettingen) and Erich Bettwieser. A gaseous or moment model of star clusters was designed. Gravothermal oscillations were detected using this model, which inspired star cluster dynamics for many years, if not decades. I could contribute a little to the model by adjusting the heat...
Stripped stars, also known as naked helium stars, are the helium cores of stars that have lost their hydrogen-rich outer layer. The recent discoveries of stripped stars have provided valuable insights into massive star evolution, as well as the evolution of stellar binaries. In my talk, I will present results from the rapid stellar evolution code METISSE, used within the binary population...
Pair-instability supernovae (PISNe) are explosions developing in the core of massive stars due to a thermonuclear, runaway process, ultimately leading to the total disruption of the progenitor.
They are expected to be the endpoint of the evolution of low-metallicity stars in the mass range between ~ 140 and 260 solar masses, and responsible for the existence of the upper mass gap in the black...
Canonical stellar evolution models from both population synthesis and detailed evolutionary codes may predict Very Massive Stars (VMS, defined as $M_{\rm ZAMS}$ > 100 M$_\odot$) to become red supergiants and expand sometimes even more than 10,000 R$_\odot$. At those masses we now know that the luminosity levels are high enough for stellar envelopes to eject mass through winds at...
Binaries are key objects in Globular Clusters and they influence their structure and dynamics. Especially interesting are pairs of stellar remnants as potential sources of gravitational wave events. Spectroscopic observations of binary stars in Globular Clusters allow to shed light on the poorly constrained period, eccentricity and mass ratio distributions, to develop an understanding of the...
We investigate the impact of massive black holes (MBHs) in merging star clusters of $M_{\star} = 5.3 \cdot 10^4 M_{\odot}$ on the escaping population of high-velocity stars and compact objects (COs) incorporating relativistic effects (up to 3.5PN order) , utilizing the GPU-accelerated N-Body code BIFROST. If the merging clusters host central MBHs of $M_{\bullet} = 10^3 M_{\odot}$ , a fraction...
In dense star clusters close encounters between stars and stellar mass black holes can have a wide variety of outcomes ranging from disruption of stars to the formation of bound quiescent binary systems as those recently discovered thanks to Gaia. The former are transients addressed as “micro-Tidal Disruption Events” (TDEs). To date, micro-TDEs have not yet been observed but they are promising...
Close binary systems are the progenitors to a variety of compact object mergers producing Type Ia supernovae and gravitational waves. While most short-period binaries are believed to have evolved through at least one common envelope (CE) phase, our understanding of CE evolution is limited due to the lack of observational benchmarks that connect the post-CE parameters with the pre-CE initial...
We explore three-body binary formation (3BBF), the formation of a bound system via gravitational scattering of three initially unbound bodies (3UB), using direct numerical integrations. For the first time, we consider systems with unequal masses, as well as finite-size and post-Newtonian effects. Our analytically derived encounter rates and numerical scattering results reproduce the 3BBF rate...
Blue straggler stars (BSS) are anomalous core hydrogen-burning stars that have undergone a rejuvenation by acquiring mass either in a direct stellar collision or through mass transfer in binaries or mergers. We have been surveying the BSS of open clusters and Galactic fields using the Ultraviolet Imaging Telescope onboard the AstroSat telescope. Together in five open clusters (NGC 7789, NGC...
Millisecond pulsars (MSPs) are neutron stars with rotational periods as low as a few milliseconds. They are formed via angular momentum transfer from accreted materials from a companion star. In the high density environment of globular clusters (GCs), MSPs are likely to form through dynamically formed interacting binaries. In fact, over 300 MSPs are detected in GCs, more than half of the known...
This study examines how the dynamical interactions in globular clusters (GCs) influence the formation and evolution of binary sources like cataclysmic variables (CVs), focusing on their X-ray luminosity distributions. Using the MOCCA simulation tool, we classify simulated GCs into three evolutionary stages (Classes I, II, and III) and observe significant differences in CV X-ray luminosities...
In the talk I would like to show the results of MOCCA simulations of globular star clusters, which show clear signs of excess of number of blue stragglers stars (BSSs) due to core collapse. The excess of BSSs happens for the core collapses happening for different times (starting from 1-2 Gyr, and up to Hubble time) and for star clusters with different parameters. This feature seems to be...
Runaway stars are thought to have been ejected from star clusters with high velocities relative to the cluster centre-of-mass motion. There are two competing mechanisms for their production: supernova-based ejections in binaries, where one companion explodes leaving no remnant and launching the other companion at the instantaneous orbital velocity, and the disintegration of triples (or...
Gaia mission offers opportunities to search for compact binaries not involved in binary interactions (hereafter inert compact binaries), and results in the discoveries of binaries containing one black hole (BH) or one neutron star (NS), called "Gaia BHs" and "Gaia NSs", respectively. Tanikawa et al. (2024, MNRAS, 527, 4031) have first pointed out that Gaia BHs can be formed much more...
In dense stellar environments, stars can collide physically. Stellar collisions are known to play a key role in shaping the stellar population in the center of stellar clusters and galactic nuclei, as well as in creating exotic stars, such as blue stragglers, and electromagnetic transients. Previous studies on stellar collisions have mostly focused on the hydrodynamical effects on the...
The exceptionally high stellar densities in the cores of globular clusters (GCs) makes them remarkable hosts for an exotic pulsar population. In this talk, I will discuss the results from the radio timing analysis of a couple of massive binary pulsars in the dense globular cluster NGC 1851, observed with the MeerKAT as a part of the TRAPUM (TRAnsients and Pulsars with MeerKAT) GC Survey. Both...
It is well-established that young stellar clusters in Magellanic Clouds (MCs) host stellar populations that are not simple. Features such as the split main sequence (MS) and the extended main sequence turn-off (eMSTO) are characteristics easily visible in all clusters younger than 2 Gyrs. Initially, these features were explained with prolonged or multiple star formation episodes, suggesting...
Despite the potential of GAIA DR3 to reveal a large population of black holes (BHs), only a few BHs have been discovered to date in orbit with luminous stars without an X-ray counterpart. It has recently been shown that black holes in orbit with main sequence companions seldom form accretion disks, from where observable X-ray flux is conventionally thought to be produced. Yet, even without...
For decades, it has been believed that globular clusters (GCs) are efficient environments for producing cataclysmic variables (CVs) due to the significant number of stellar interactions among their members. However, models in the last years have cast doubt on the validity of this scenario. In this study, I present the results of the first analysis of detectable CVs in core-collapsed and...
In collisional system simulations such as globular clusters, stable criteria for hierarchical triple systems are essential. SDAR (Wang et al. 2020) is a method capable of rapidly computing binaries, particularly hierarchical triple systems, but its efficiency depends on the accuracy of the stability criteria for these systems. Traditional criterion is expressed by the parameter $Q =...
Ultra-Luminous X-ray Sources (ULXs), which emit more X-rays than typical accreting black holes, remain enigmatic objects in astrophysics. With only around 20 ULXs potentially residing in Globular Clusters (GCs), they pose challenging targets for study. Previous research predominantly focused on ULXs in the field, yet in the dense environment of GCs, where stars are densely packed, dynamics...
Stars do not form in isolation but together with other stars, often in a clustered environment. During the dynamical evolution of these environments, stars will interact with each other. These encounters will affect any planetary systems that are in the process of forming around them. Many typical fly-by simulations focus on a single fly-by event's effect on a planetary system. However, during...
Discoveries of Milky Way stars with velocities in excess of the Galactic escape speed (~500 km/s at the Solar position) have been reported with increasing frequency in the era of large Galactic surveys. These 'hyper-velocity stars' serve as a fascinating probe of the extreme dynamical and astrophysical phenomena which produce them, such dynamical interactions with Sgr A* or supernovae within...
In the first part of the presentation, I shall recapitulate my recent endeavours in investigating the role of dynamical interactions in moderate mass star clusters in producing stellar-mass binary black hole (BBH) mergers over cosmic time. Dynamical BBH mergers are obtained from long-term direct N-body evolutionary models of ~10^4 M_sun, pc-scale young massive clusters evolving into...
One of the great challenges for gravitational-wave astrophysics is disentangling different formation channels of binary black-hole (BBH) mergers. Achieving this requires in-depth understanding of BBH formation pathways and robust predictions for observable channel characteristics. We tackle this challenge for binary evolution scenarios by systematically modeling mass transfer evolution in...
Repeated stellar collisions and hierarchical mergers in dense and massive star clusters are among the most straightforward mechanisms to produce intermediate-mass black holes (IMBHs).
In my talk, I will investigate the formation channels of IMBHs in globular clusters up to $10^6\,\rm{M_{\odot}}$. To do this, I will rely on an extensive set of accurate N-body models run with the...
Intermediate mass black holes (IMBHs) serve as a crucial link between stellar-mass black holes, resulting from the death of massive stars, and supermassive black holes residing at the center of galaxies. Yet, we do not fully understand the necessary conditions for IMBH production, raising questions about whether they could constitute a completely distinct category of black holes.
Star...
The intermediate mass black hole (IMBH) regime is still poorly constrained with few detections between 150 and 10$^5$ M$_\odot$.
An IMBH in ω Centauri, the Milky Way’s most massive globular cluster, has been suspected for almost two decades, but all previous detections have been questioned due to their assumptions and the possible mass contribution of a central cluster of stellar mass black...
Globular clusters (GCs) are thought to harbor the long-sought population of intermediate-mass black holes (IMBHs). We present a systematic search for a putative IMBH in 81 Milky Way GCs, based on archival {\it Chandra} X-ray observations. We find in only six GCs a significant X-ray source positionally coincident with the cluster center, which have 0.5--8 keV luminosities between $\sim1\times...
We present the results of direct N-body simulations focusing on stellar discs interacting with a central supermassive black hole (SMBH) and an off-plane intermediate mass black hole (IMBH) embedded within a spherical star cluster. For models with a high-mass IMBH ($m_{\bullet} \simeq M_{\rm d}$) on a retrograde orbit with respect to the stellar disc, we find that the IMBH tends to anti-align...
Next-generation (XG) ground-based gravitational wave observatories are expected to be sensitive to mergers of intermediate-mass black holes (IMBHs) with a total source-frame mass in the hundreds out to a high redshift. Runaway tidal encounters lead to the formation of IMBHs in the cores of dense stellar clusters. I will discuss how single IMBH–IMBH merger events, occurring after the...
Supermassive black holes (SMBHs) are found to co-exist with a nuclear star cluster (NSC) in the nuclei of most galaxies. The work presented in this talk builds on the idea that the NSC forms before the SMBH through the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC, and form an SMBH. To check the...
There are indications that stellar-origin black holes (BHs) are efficiently paired up in binary black holes (BBHs) in Active Galactic Nuclei (AGN) disc environments, which can undergo interactions with single BHs in the disc. Such binary-single interactions can potentially lead to an exceptionally high fraction of gravitational-wave mergers with measurable eccentricity in LIGO/Virgo/KAGRA. We...
Estimating the spin of SgrA∗ is one of the current challenges we face in understanding the center of our Galaxy. In the present work, we show that detecting the gravitational waves (GWs) emitted by a brown dwarf inspiraling around SgrA∗ will allow us to measure the mass and the spin of SgrA∗ with unprecedented accuracy. Such systems are known as extremely large mass-ratio inspirals (XMRIs) and...
It is well established that massive black holes reside in the central regions of virtually all types of known galaxies. Recent observational and numerical studies however challenge this picture, suggesting that intermediate-mass black holes in dwarf galaxies may be found on orbits far from the center. In this talk, I will present my recent work on the dynamics of off-center black holes in...
LIGO/VIRGO/KAGRA collaboration announced over 90 gravitational waves detections from double compact objects (DCOs) mergers, however, the origin and evolution scenario of their progenitors remains elusive.
One of the promising candidates for DCOs progenitors are the X-ray binaries (XRBs) where X-ray emission arises from the accretion of matter transferred from the companion star onto a black...
With nearly 200 hundred gravitational-wave detection candidates reported by the LIGO-Virgo-KAGRA Collaboration over the past decade, we are now entering an era where the statistical analysis of the properties of double compact objects provides us with a better understanding of the physical processes behind these extreme objects. However, the question of the astrophysical origin of merging...
Dense stellar clusters are prime environments for the formation and evolution of bound binary black hole (BBH) systems, leading to eventual mergers. These BBHs can form through direct interactions among stellar objects or evolve from primordial binaries — binaries that originated within the cluster. Importantly, the dynamical interactions within these clusters have the potential to...
Isolated evolution of massive stars is expected to leave a “gap" in the mass spectrum of black holes (BHs) at birth between ~40-120 Msun due to (pulsational) pair-instability supernovae ((P)PISN). Recent detections of gravitational waves (GWs) from mergers of BHs with pre-merger source-frame individual masses in this so-called upper mass-gap, have created immense interest in a detailed...
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...
A number of different hypotheses about the origin of Supermassive black holes (SMBHs) in the galactic centres was proposed. One formation channel that we investigate in our project is the gravitational runaway scenario, that suggests an SMBH seed to form by runaway collisions in dense star systems like globular clusters (GCs). We focused on two promising candidates that can host such a massive...
Although great progress has been made the last years on the shape of
the Stellar Mass Function and the dynamics of stellar clusters in more
evolved clusters, less is known on the earliest stages of star
formation. Here we present recent JWST observations in conjunction
with previous HST and VLT observations of a still forming star
cluster, identified by a large molecular infall. The...
Tidal disruptions of stars by massive black holes (MBHs) in dense stellar clusters may be an important channel for MBH growth. While full tidal disruption events (FTDEs) have been studied extensively, recently the focus has shifted to understanding the impact of partial tidal disruption events (PTDEs). We study MBH growth in dense star clusters through full and partial tidal disruption events...
Over a third of all observed millisecond pulsars appear in Galactic globular clusters, which collectively account for less than 0.05% of the total number of stars in the Milky Way. Recently, there have been radio observations (with MeerKAT) of a possible millisecond pulsar-black hole (mass gap) eccentric binary in the globular cluster NGC 1851. On the other hand, the current generation of...
