arXiv subjects

Fotios Fronimos Pouliasis

Publications and source records attributed to Fotios Fronimos Pouliasis.

4 recordsLinked to original sources

arXiv2026

Fast Dynamical Modelling of Milky Way Globular Clusters -- II. Impacts of Black Hole Prescriptions

The populations of stellar-mass black holes (BHs) in globular clusters (GCs) play a key role in their dynamical evolution, however the mechanisms surrounding their formation and retention are uncertain. In this work, we extend the analysis of Paper I by fitting coupled rapid cluster evolution and multimass equilibrium models to a large sample of Milky Way GCs, under a variety of prescriptions for stellar evolution, BH formation and supernovae (SN) natal kicks. We explore the impacts of adopting SSE or PARSEC (through SEVN) prescriptions for BH initial-final mass relations, the rapid or delayed SN fallback mechanisms, and an ad hoc grid of kick strengths ejecting between 40 and 80 per cent of all BHs formed. All models reproduce the same present-day conditions despite starting from notably different initial BH populations, due to the correlation found between the initial cluster densities and initial BH mass fractions. A linear relationship is found between the (log) initial half-mass density and the initial BH mass fraction, with the SEVN models resulting in median densities ($ρ_{h,0} \sim 10^{7.2\pm1.1}\,{M_\odot pc^{-3}}$) nearly an order of magnitude higher than those of SSE ($ρ_{h,0} \sim 10^{6.4\pm0.9}\,{M_\odot pc^{-3}}$). We also find that both the bottom-light initial mass functions and the present-day BH mass fractions previously inferred are relatively robust against the stellar evolution models and natal kick prescriptions assumed. Finally, we discuss the implications of these results on the expected numbers and properties of dynamical binary-BH mergers, and the growth of intermediate-mass BHs.

astro-ph.GA↗

arXiv2026

Fast Dynamical Modelling of Milky Way Globular Clusters -- I. Implications for Initial Cluster Densities

We infer the initial conditions of Milky Way (MW) globular clusters (GCs) from present-day observations, through the coupling of recently updated rapid cluster evolution models with multimass equilibrium models. This novel method is validated by fitting to simulated observations of a large grid of star-by-star Monte Carlo models, demonstrating that we are able to recover cluster properties like the total mass, half-mass radius/density and black hole (BH) mass fraction, both initially and at the present day, across a large region of parameter space. We apply this framework to a sample of 40 MW GCs, fitting to a suite of observed radial profiles of number densities, proper motions, line-of-sight velocities and stellar mass functions. From these fits we infer a distribution of initial half-mass densities with a median and $1σ$ width, across our sample, of $ρ_{h,0} = 10^{6.4\pm0.9}\,{M_\odot pc^{-3}}$, higher than what is found for young massive clusters in the Local Universe and in line with young clusters at high redshift. We also find stellar initial mass functions that are bottom-light in comparison to canonical prescriptions, and relatively small present-day BH mass fractions ($\lesssim 1.5\%$). We discuss the implications of these initial cluster densities for observations of high-redshift proto-GCs, binary BH merger rates and intermediate-mass BHs (IMBHs) in GCs. Finally, we quantify how these densities may depend on assumptions typically made surrounding BH formation and natal kicks.

astro-ph.GA↗

arXiv2026

cBHBd: A fast code for the evolution of tidally limited star clusters and their binary black hole mergers

The evolution of star clusters is driven by stellar mass loss, two-body relaxation, and evaporation in the Galactic tidal field. Fast modeling tools are crucial for exploring diverse initial conditions and predicting cluster populations and their contribution to gravitational wave (GW) sources over cosmic timescales. We present an improved version of the clusterBHBdynamics (cBHBd) code, designed to evolve star clusters containing stars and stellar-mass black holes (BHs). We improve the treatment of evaporation in the Galactic tidal field and include the effects of metallicity and stellar mass functions. We also introduce new prescriptions for GW captures during BBH-BBH interactions and between resonant interactions due to distant encounters that increase BBH eccentricities. The updated cBHBd is validated against Cluster Monte Carlo (CMC) models and $N$-body simulations spanning a range of cluster properties. Seven model parameters are fitted to the CMC results with nested sampling. With the best-fit values, the evolution of the cluster mass, half-mass radius, and BH population over 13 Gyr is reproduced to within $\sim10\%$. The new GW capture prescriptions allow cBHBd to reproduce BBH merger rates from CMC models of massive clusters ($\gtrsim10^5,M_\odot$) and direct $N$-body models of lower-mass clusters ($\lesssim10^5,M_\odot$) to within $\sim20\%$. The improved cBHBd provides a fast and flexible tool for large-scale star cluster studies. With a runtime of about one second per cluster, it enables applications such as searches for globular cluster initial conditions, stellar stream modeling, and GW population synthesis.

astro-ph.GA↗

arXiv2026

Repopulating the pair-instability mass gap without sustained growth to massive IMBHs: the case of 47\,Tuc

We model the formation and retention of the most massive black hole (BH) in 47~Tuc using the semi-analytical code \texttt{cBHBd}, coupling cluster evolution with binary BH dynamics and computing merger-remnant masses, spins, and gravitational-wave recoil kicks via numerical-relativity surrogate prescriptions. We evolve 80\,000 cluster realisations spanning initial masses, densities, IMFs, and metallicities, in both a baseline scenario ($m_{\rm max} = 130\,\mathrm{M}_{\odot}$) and an extended-IMF scenario with ${\sim}\,50-110$ primordial BH seeds above the pair-instability gap ($M_{\rm BH} \sim 130-700\,\mathrm{M}_{\odot}$). Selecting models reproducing 47~Tuc's present-day mass and half-mass radius, we find hierarchical mergers alone yield a most massive retained BH of $M_{\rm BH} \sim 45-70\,\mathrm{M}_{\odot}$ with spin $χ_{\rm BH} \sim 0.65$, limited to ${\sim}\,1-3$ mergers, as second-generation remnants acquire spin $χ\sim 0.7$ that amplifies recoil kicks in subsequent generations. When primordial seeds are included, the retained-mass distribution becomes bimodal -- in ${\sim}\,90\%$ of realisations all seeds are ejected, but in ${\sim}\,10\%$ a massive seed ($M_{\rm BH} \gtrsim 450\,\mathrm{M}_{\odot}$) survives -- while the joint mass-spin distribution is trimodal; seeds surviving via stellar-mass BH mergers retain low spin ($χ\lesssim 0.3$), whereas seed-seed mergers produce high-mass, high-spin remnants ($χ\sim 0.65-0.7$), yielding 90th-percentile retained masses of ${\sim}\,500-1100\,\mathrm{M}_{\odot}$. Both scenarios are consistent with the $3σ$ dynamical upper limit of $578\,\mathrm{M}_{\odot}$. Our results favour a dark-remnant subsystem over a single massive IMBH and provide a spin-mass diagnostic testable with LIGO-Virgo-KAGRA, the Einstein Telescope, Cosmic Explorer, and LISA.

astro-ph.HE↗