arXiv subjects

Manuel Arca Sedda

Publications and source records attributed to Manuel Arca Sedda.

At least 19 recordsLinked to original sources

arXiv2026

Assessing the Impact of Instrumental Requirements on the Scientific Performance of the Einstein Telescope

We investigate the relationship between instrumental requirements and the scientific performance of the Einstein Telescope (ET), a third-generation (3G) gravitational-wave (GW) observatory. Different technical design choices result in distinct noise budgets, ultimately shaping the detector's scientific capabilities. To systematically assess and compare their impact, we define a comprehensive set of performance metrics spanning compact binary coalescence (CBC) detection and parameter estimation, as well as other sources, including stochastic GW backgrounds, isolated spinning neutron stars, and core-collapse supernovae (CCSNe). We build a comparative reference framework that links degradations in specific noise contributions and frequency bands to losses in scientific capabilities. We consider a representative selection of technical parameters, such as coating and suspension temperatures, the filter cavity length in the low-frequency instrument, and the beam size in the high-frequency instrument. We evaluate how sensitivity variations across specific frequency bands affect different scientific objectives. We quantify how the sensitivity below 30 Hz impacts the detectability of massive and/or high-redshift sources and the reconstruction of long-duration CBC signals, affecting early warning and sky localization for binary neutron stars (BNSs). Sensitivity in the 30-450 Hz range governs most CBC parameter-estimation metrics, while high-frequency sensitivity above ~450 Hz predominantly impacts BNS post-merger studies and CCSN detectability, with modest effects on detection rates. Even with the most significant degradations considered, the ET science case remains robust overall. Our results provide a comprehensive benchmark linking scientific objectives to instrumental requirements, particularly important as the final design and infrastructure of 3G observatories are being defined.

astro-ph.IM↗

arXiv2026

Pebbles to Gems: Intermediate-mass black holes in the first star clusters

The rapid assembly of supermassive black holes (SMBHs) observed at $z\gtrsim7$ requires efficient seeding mechanisms in the early Universe. Population III (Pop. III) star clusters have recently emerged as a promising pathway that may bridge the gap between traditional light- and heavy-seed scenarios by producing intermediate-mass black holes (IMBHs) with masses up to $\sim10^4\,\rm M_{\odot}$. We investigate the properties and number densities of IMBHs forming in Pop. III star clusters with masses $M_{\rm cl}\sim10^3-4\times10^5\,\rm M_{\odot}$, and hosted in isolated dark matter minihalos, using a suite of direct $N$-body simulations. We adopt cosmologically motivated initial conditions and explore different stellar evolution prescriptions, binary orbital parameter distributions, and cluster dynamical configurations. By $z\sim19$, the IMBH mass function consistently peaks at $m_{\rm IMBH}\sim200\,\rm M_{\odot}$, with number densities of $n_{\rm IMBH}\sim0.2-5\,\rm cMpc^{-3}$. In sufficiently dense and massive clusters, IMBHs with masses $>10^3\,\rm M_{\odot}$ can already form by $z\sim19$, reaching number densities of $n_{\rm IMBH}\sim10^{-4}-10^{-2}\,\rm cMpc^{-3}$. The most massive IMBHs in our models reach $\sim6200\,\rm M_{\odot}$ through the collapse of very massive stars assembled by repeated stellar collisions, a process enhanced in fractal clusters. Lower-mass IMBHs form instead predominantly through single and binary stellar evolution and binary stellar mergers. We find that models combining large stellar radii and tight binaries produce the highest IMBH abundances relative to isolated Pop. III evolution. Owing to the high retention fraction of IMBHs ($\gtrsim88\%$), massive dense Pop. III star clusters can act as efficient incubators of both light and heavy SMBH seeds, even if only a fraction of Pop. III stars formed in such environments.

astro-ph.GA↗

arXiv2026

The impact of stellar binaries and star cluster dynamics on pair-instability supernovae

Pair-instability supernovae (PISNe) are among the most luminous transients in the Universe. However, they have never been confidently observed. Solving this puzzle would have key implications for several astrophysical topics, including galaxy chemical enrichment, the interpretation of gravitational waves from binary black hole mergers, and the nature of red dropout sources seen by JWST. With this aim, we present the first in-depth study of PISN occurrence in binary stars, both in isolation and in dense star clusters. We employ the SEVN code, with PARSEC stellar tracks, to evolve a suite of 35 synthetic binary populations, including variations on formation channels, cluster properties, and upper limit of the stellar initial mass function. We find that binary interactions can boost the PISN rate by up to threefold, relative to single stars, whereas binary hardening can either enhance or suppress PISN production, depending on whether the progenitors are primordial or dynamically formed. Moreover, we showcase how our comprehensive framework for the cosmic PISN rate can be used to constrain uncertain aspects of stellar and galaxy evolution models, via comparison with observations, including the recipes for stellar-wind mass loss in very-massive stars, and the galaxy metallicity distribution throughout the Universe.

astro-ph.HE↗

arXiv2026

Intermediate-mass black hole seeding in galactic nuclei from star cluster migration

Nuclear star clusters are one of the most favorable sites to host hierarchical black hole (BH) mergers, potentially bridging the gap from stellar-mass to massive BHs. However, their assembly and the evolution of their BH populations remain poorly constrained. We investigate the process of intermediate-mass BH (IMBH) seeding in galactic nuclei from star cluster migration. We introduce inSpyral, a new semi-analytic model that draws star cluster populations from a galaxy formation model (L-Galaxies 2020),and integrates their evolution across a wide range of spatial scales, from BH core dynamics to the orbital motion in the host galaxy. We find that dynamical friction drives the inspiral of the most massive clusters in galaxies with $M_{\mathrm{\star, gal}} \lesssim 5 \times 10^{10} \,\mathrm{M_\odot}$, seeding their nuclei with IMBHs as early as $z \sim 6$. The BH mass distribution from BH mergers in migrating clusters extends to $\sim 300 \, \mathrm{M_\odot}$, a factor of five above the upper limit from in-situ formation. If clusters form with sub-parsec scale radii ($\lesssim 0.5 \, \mathrm{pc}$), hierarchical mergers significantly enhance BH mass growth before migration, and seed galactic nuclei with IMBHs above $10^4 \, \mathrm{M_\odot}$. The most massive and highly spinning gravitational-wave events are well reproduced by BH mergers involving second-generation remnants that experienced relatively small relativistic kicks ($\lesssim 100 \, \mathrm{km \, s^{-1}}$). GW231123 is consistent with BH mergers between a third-generation primary and a second-generation secondary, which occur in star clusters with mass $> 2 \times 10^{6} \, \mathrm{M_\odot}$.

astro-ph.GA↗

arXiv2026

Gravitational Waves from the Cosmic Dawn: Tracing Cosmic Black Hole Binaries with ET, LGWA and LISA

Next generation detectors, such as LISA, LGWA, and ET will, for the first time, probe the high redshift Universe, offering unique insight into the birth, growth, and dynamics of the first black holes (BHs) during their earliest stages formation. We aim to predict merger rates and gravitational wave (GW) signatures of "cosmic" binary BHs, forming as a result of galaxy mergers, at z>=4. We investigate how BH seeding, accretion physics and dynamical delays affect their properties and detectability across cosmic epochs. We use the semi-analytic model Cosmic Archaeology Tool (CAT) to trace the evolution and delayed-mergers, driven by dynamical friction, of BH binaries formed from light, medium-weight and heavy seeds, under Eddington-limited (EL) and super-Eddington (SE) accretion prescriptions. We employ the GWFish package to evaluate their GW signals and detectability by LISA, LGWA and ET. Our results show the impact of BH accretion and seeding prescriptions on the properties and distribution of detectable sources. In the EL model, the detected populations are dominated by nearly equal-mass binaries. In contrast, SE growth leads to lower mass ratios for LISA detections and medium ratios for ET and LGWA. We present the total detection rates predicted under the two accretion scenarios. The SE model allows BHs to grow faster, transferring a significant fraction of detectable systems from the ET band to the LISA band, compared to the EL model. As a result, the predicted LISA detection rate increases from ~32 yr^-1 in the EL case to ~64 yr^-1 in the SE scenario, and the ET detection rate reduces from ~64 yr^-1 in the EL model to only ~4 yr^-1 in the SE scenario. LGWA yields comparable detection rates in both scenarios (~21 yr^-1 in EL and ~12 yr^-1 in SE). The combined information encoded in mass ratios, redshift evolution and merger rates emerge as a promising diagnostic of early BH growth.

astro-ph.GA↗

arXiv2026

Direct N-body simulations of rotating and extremely massive Population III star clusters

Aims. We present eight direct N-body simulations with NBODY6++GPU of extremely massive, initially rotating Population III star clusters with 1.01 x 10^5 stars. Methods. Our models include primordial binaries, a continuous initial mass function, differential rotation, tidal mass loss, updated fitting formulae for extremely massive metal-poor Population III stars, and general-relativistic merger recoil kicks. We assess their impact on cluster dynamics. Results. All runs form black holes below, within, and above the pair-instability gap, with multi-generation growth. Faster-rotating clusters core-collapse earlier; post-collapse clusters host a rotating, axisymmetric subsystem of intermediate-mass black holes (IMBHs) at the centre and an expanding halo of lower-mass objects. Pair-instability supernovae and compact-object formation at ~2-3 Myr sharply reduce total mass and a large fraction of the cluster's angular momentum. All Population III clusters in our simulations have the gravothermal-gravogyro catastrophe phase. Conclusions. We confirm two of the hypothesized formation channels of galactic nucleus seed black holes: gravitational runaway mergers of black holes and of Population III stars, which core-collapse into IMBHs thereafter. A higher initial star cluster bulk rotation correlates with earlier core collapse and, in the event counts reported here, with more coalescences and collisions, as well as lower retained (compact) binary abundances. Initial bulk rotation is a primary control parameter of cluster evolution: faster rotation accelerates early angular-momentum transport, gravothermal collapse, mass segregation, and amplifies post-collapse expansion, which also favours the formation of a compact central IMBH subsystem.

astro-ph.GA↗

arXiv2026

Comparing astrophysical models to gravitational-wave data in the observable space

Comparing population-synthesis models to the results of hierarchical Bayesian inference in gravitational-wave astronomy requires a careful understanding of the domain of validity of the models fitted to data. This comparison is usually done using the inferred astrophysical distribution: from the data that were collected, one deconvolves selection effects to reconstruct the generating population distribution. In this paper, we demonstrate the benefits of instead comparing observable populations directly. In this approach, the domain of validity of the models is trivially respected, such that only the relevant parameter space regions as predicted by the astrophysical models of interest contribute to the comparison. With this in mind, it can be useful to fit the observed population directly, rather than effectively deconvolving the selection effects only to fold them back in when reconstructing the observable population. We clarify that unbiased inference of the observable compact-binary population is indeed possible. Crucially, this approach still requires incorporating selection effects, but in a manner that differs from the standard implementation. We apply our observable-space reconstruction to LIGO-Virgo-KAGRA data from their third observing run and illustrate its potential by comparing the results to the predictions of a fiducial population-synthesis model.

gr-qc↗

arXiv2026

Isolated or Dynamical? Tracing Black Hole Binary Formation through the Population of Gravitational-Wave Sources

The population of binary black hole (BBH) mergers observed by the LIGO-Virgo-KAGRA (LVK) collaboration offers a window into the cosmic evolution of compact binaries and their formation. We employ the semi-analytic population-synthesis code B-POP to model BBHs assembled through isolated binary evolution and dynamical interactions in young, globular, and nuclear star clusters. Our framework incorporates star formation history, metallicity evolution, and single and binary stellar evolution to quantify their impact on the observable properties of the BBH population and on the relative contribution of distinct formation channels. Our models are characterized by a merger rate, $\mathcal{R} = 17.5-24.1\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$, broadly consistent with LVK constraints. Moreover, the predicted distributions of primary mass, mass ratio, and effective inspiral spin parameter are compatible with those inferred from current LVK observations. Our primary-mass distribution is dominated by isolated binaries at $m_1 < 20$ M$_\odot$, while dynamically assembled first- and higher-generation mergers dominate at larger masses. As a consequence, the sub-population of mergers with $m_1 > 45$ M$_\odot$ exhibits a nearly flat mass-ratio distribution and distinctive spin properties. We leverage our models to explore how: (i) the fraction of stars in isolated binaries and the fraction of stellar mass bound in clusters regulate the merger rate; (ii) common-envelope physics shapes the primary-mass distribution and its redshift evolution; (iii) the inclusion of stellar-collision products enhances the formation of higher-generation mergers; and (iv) the natal spin distribution influences the effective spin. Using our models to assess possible origins of selected GW events, we illustrate how the complexity of the underlying astrophysical processes can hinder the possibility to draw definitive conclusions.

astro-ph.GA↗

arXiv2026

Teen TITANS simulations -- I. Inefficient intermediate-mass black hole seeding via stellar collisions in young massive clusters

Young massive clusters (YMCs) provide favorable environments for frequent stellar collisions, potentially leading to the formation of very massive stars (VMSs) and seeds of intermediate-mass black holes (IMBHs). We investigate the role of repeated stellar collisions in YMCs using TITANS, a new suite of 18 direct $N$-body simulations. Our models span cluster masses $10^5 - 10^6\,\rm M_\odot$, half-mass densities $ρ_{\rm h}=100 - 10^5\,\rm M_\odot\,pc^{-3}$, and include high primordial binary fractions, consistent with observations of massive stars in young clusters. Overall, our simulations assume cluster properties that are typical of YMCs in the low-redshift Universe. We find that repeated stellar collisions are efficient only in the densest clusters with short relaxation times and are absent in systems with $ρ_{\rm h}<500\,\rm M_\odot\,pc^{-3}$ and $t_{\rm rh}>1.3\,\rm Gyr$. Rapid mass segregation allows massive stars to sink to the cluster center, merge, and undergo subsequent collisions, even in clusters with long core-collapse times. However, collision chains are typically triggered by primordial binary mergers and usually involve only two collisions. In our simulations, only three VMSs form through repeated collisions and reach $m_*>330\,\rm M_\odot$, while most VMSs have $m_*<300\,\rm M_\odot$ and form through primordial binary mergers. None constitute viable IMBH seeds, as their helium cores fall in the (pulsational) pair-instability regime. We form five IMBHs from stellar collisions involving stars at different evolutionary stages, while the dominant channel is the merger of stellar-mass black holes, producing twelve IMBHs. For properties typical of local YMCs, stellar collision chains are therefore inefficient in producing IMBHs more massive than $140\,\rm M_\odot$, as most collisionally formed VMSs attain masses that fall in the pair-instability regime.

astro-ph.GA↗

arXiv2025

Rapid formation of a very massive star >50000 $M_\odot$ and subsequently an IMBH from runaway collisions. Direct N-body and Monte Carlo simulations of dense star clusters

Context. We present simulations of a massive young star cluster using \textsc{Nbody6++GPU} and \textsc{MOCCA}. The cluster is initially more compact than previously published models, with one million stars, a total mass of $5.86 \times 10^5~\mathrm{M}_{\odot}$, and a half-mass radius of $0.1~\mathrm{pc}$. Aims. We analyse the formation and growth of a very massive star (VMS) through successive stellar collisions and investigate the subsequent formation of an intermediate-mass black hole (IMBH) in the core of a dense star cluster. Methods. We use both direct \textit{N}-body and Monte Carlo simulations, incorporating updated stellar evolution prescriptions (SSE/BSE) tailored to massive stars and VMSs. These include revised treatments of stellar radii, rejuvenation, and mass loss during collisions. While the prescriptions represent reasonable extrapolations into the VMS regime, the internal structure and thermal state of VMSs formed through stellar collisions remain uncertain, and future work may require further refinement. Results. We find that runaway stellar collisions in the cluster core produce a VMS exceeding $5 \times 10^4~\mathrm{M}_{\odot}$ within 5 Myr, which subsequently collapses into an IMBH. Conclusions. Our model suggests that dense stellar environments may enable the formation of very massive stars and massive black hole seeds through runaway stellar collisions. These results provide a potential pathway for early black hole growth in star clusters and offer theoretical context for interpreting recent JWST observations of young, compact clusters at high redshift.

astro-ph.GA↗

arXiv2025

Black Hole - Neutron Star and Binary Neutron Star Mergers from Population III and II stars

Population III (Pop.$~$III) stars are expected to be massive and to undergo minimal mass loss due to their lack of metals, making them ideal progenitors of black holes and neutron stars. Here, we investigate the formation and properties of binary neutron star (BNS) and black hole-neutron star (BHNS) mergers originating from Pop.$~$III stars, and compare them to their metal-enriched Population II (Pop.$~$II) counterparts, focusing on their merger rate densities (MRDs), primary masses and delay times. We find that, despite the high merger efficiency of Pop.$~$III BNSs and BHNSs, their low star formation rate results in a MRD at least one order of magnitude lower than that of Pop.$~$II stars. The MRD of Pop.$~$III BNSs peaks at redshift $z\sim15$, attaining a value $\mathcal{R}_{\rm BNS}(z\sim15) \sim 15\,\rm Gpc^{-3}\,yr^{-1}$, while the MRD of Pop.$~$III BHNSs is maximum at $z\sim13$, reaching a value $\mathcal{R}_{\rm BHNS}(z\sim13) \sim 2\,\rm Gpc^{-3}\,yr^{-1}$. Finally, we observe that the black hole masses of Pop.$~$III BHNS mergers have a nearly flat distribution with a peak at $\sim 20\,\rm M_{\odot}$ and extending up to $\sim 50\,\rm M_{\odot}$. Black holes in Pop.$~$II BHNS mergers show instead a peak at $\lesssim 15\,\rm M_{\odot}$. We consider these predictions in light of recent gravitational-wave observations in the local Universe, finding that a Pop.$~$III origin is preferred relative to Pop.$~$II for some events.

astro-ph.GA↗

arXiv2025

Fast and accurate parameter estimation of high-redshift sources with the Einstein Telescope

The Einstein Telescope (ET), along with other third-generation gravitational wave (GW) detectors, will be a key instrument for detecting GWs in the coming decades. However, analyzing the data and estimating source parameters will be challenging, especially given the large number of expected detections-on the order of $10^5$ per year-which makes current methods based on stochastic sampling impractical. In this work, we use Dingo-IS to perform neural posterior estimation (NPE) of high-redshift events detectable with ET in its triangular configuration. NPE is a likelihood-free inference technique that leverages normalizing flows to approximate posterior distributions. After training, inference is fast, requiring only a few minutes per source, and accurate, as corrected through importance sampling and validated against standard Bayesian inference methods. To confirm previous findings on the ability to estimate parameters for high-redshift sources with ET, we compare NPE results with predictions from the Fisher information matrix (FIM) approximation. We find that NPE correctly recovers the eight degenerate sky modes induced by the triangular detector geometry, missed by the FIM analysis, resulting in an underestimation of sky localization uncertainties for most sources. FIM also overestimates the uncertainty in luminosity distance by a factor of $\sim 3$ on average when the injected luminosity distance is $d^{\mathrm{inj}}_{\mathrm{L}} > 10^5~$Mpc, further confirming that ET will be particularly well suited for studying the early Universe.

astro-ph.HE↗

arXiv2025

Seeds to success: growing heavy black holes in dense star clusters

The observational dearth of black holes (BHs) with masses between $\sim$100 and 100,000 $M_\odot$ raises questions about the nature of intermediate-mass black holes (IMBHs). Proposed formation channels for IMBHs include runaway stellar collisions and repeated binary BH (BBH) mergers driven by dynamical interactions in stellar clusters, but the formation efficiency of these processes and the associated IMBH occupation fraction are largely unconstrained. In this work, we study IMBH formation via both mechanisms in young, globular, and nuclear star clusters. We carry out a comprehensive investigation of IMBH formation efficiency by exploring the impact of different seeding models and star cluster formation histories. We employ a new version of the B-POP population synthesis code, able to model several seeding mechanisms as well as hierarchical BBH mergers. We quantify the efficiency of IMBH production across different cluster families, and estimate the fraction of BBH mergers involving an IMBH primary. Comparison with low-redshift IMBH candidates suggests that, depending on the seeding mechanism, stellar collisions can play a pivotal role in explaining potential IMBHs in local globular clusters. Our simulations highlight stellar collisions as the primary IMBH formation channel across a wide range of cluster types. They further suggest that wandering IMBHs may populate Milky Way-like galaxies and that correlations between cluster and IMBH masses can help distinguish the origins of Galactic globular clusters.

astro-ph.GA↗

arXiv2025

Assembling GW231123 in star clusters through the combination of stellar binary evolution and hierarchical mergers

GW231123 is the most massive binary black hole (BBH) merger detected to date by the LIGO-Virgo-KAGRA collaboration. With at least one black hole (BH) in the upper-mass gap and both BHs exhibiting high spins ($χ_{1,2} \gtrsim 0.8$), this event challenges standard isolated binary evolution models. A compelling alternative is a dynamical origin in star clusters, where stellar binaries and hierarchical mergers may both contribute to the formation of similar BBHs. In this work, we investigate the formation of GW231123-like events in different cluster environments using the B-POP semi-analytic population synthesis code. We find that low-metallicity environments ($Z \lesssim 0.002$) are ideal for producing BBH mergers similar to GW231123. In young and globular clusters, these BBHs have components formed in stellar binaries, whilst in nuclear clusters there is also a significant contribution from BHs built-up via hierarchical mergers. Natal spins of BHs formed in stellar binaries are crucial to find GW231123 analogs. In particular, our models suggest that BHs from stellar binaries are likely characterized by high-spins. Simulated GW231123-like systems exhibit short delay times, $t_\mathrm{del} \sim 0.1 - 1$ Gyr, which suggests their progenitors formed close to the inferred merger redshift ($z = 0.39^{+0.27}_{-0.24}$). We argue that star clusters in metal-poor dwarf galaxies or Milky Way-like galaxies are ideal nurseries, inferring an upper limit to the local merger rate of $\mathcal{R} \sim 1.6\times10^{-3} - 0.16$ yr$^{-1}$ Gpc$^{-3}$ for nuclear clusters, $\sim 0.036 - 0.72$ yr$^{-1}$ Gpc$^{-3}$ for globular clusters, and $4\times10^{-4}-0.041$ yr$^{-1}$ Gpc$^{-3}$ for young clusters.

astro-ph.GA↗

arXiv2025

The Science of the Einstein Telescope

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

gr-qc↗

arXiv2024

The Lunar Gravitational-wave Antenna: Mission Studies and Science Case

The Lunar Gravitational-wave Antenna (LGWA) is a proposed array of next-generation inertial sensors to monitor the response of the Moon to gravitational waves (GWs). Given the size of the Moon and the expected noise produced by the lunar seismic background, the LGWA would be able to observe GWs from about 1 mHz to 1 Hz. This would make the LGWA the missing link between space-borne detectors like LISA with peak sensitivities around a few millihertz and proposed future terrestrial detectors like Einstein Telescope or Cosmic Explorer. In this article, we provide a first comprehensive analysis of the LGWA science case including its multi-messenger aspects and lunar science with LGWA data. We also describe the scientific analyses of the Moon required to plan the LGWA mission.

gr-qc↗

arXiv2024

The boring history of Gaia BH3 from isolated binary evolution

Gaia BH3 is the first observed dormant black hole (BH) with a mass of $\approx{30}$ M$_\odot$ and represents the first confirmation that such massive BHs are associated with metal-poor stars. Here, we explore the isolated binary formation channel for Gaia BH3 focusing on the old and metal-poor stellar population of the Milky Way halo. We use the MIST stellar models and our open-source population synthesis code SEVN to evolve $5.6 \times 10^8$ binaries exploring 20 sets of parameters. We find that systems like Gaia BH3 form preferentially from binaries initially composed of a massive star ($40-60$ M$_\odot$) and a low mass companion ($<1$ M$_\odot$) in a wide ($P>10^3$ days) and eccentric orbit ($e>0.6$). Such progenitor binary stars do not undergo any Roche-lobe overflow episode during their entire evolution, so that the final orbital properties of the BH-star system are determined at the core collapse of the primary star. Low natal kicks ($\lesssim$ 10~km/s) significantly favour the formation of Gaia BH3-like systems, but high velocity kicks up to $\approx 220$ km/s are also allowed. We estimate the formation efficiency for Gaia BH3-like systems in old ($t>10$ Gyr) and metal-poor ($Z<0.01$) populations to be $\sim 4 \times 10^{-8}$ M$_\odot^{-1}$ (for our fiducial model), representing $\sim 3\%$ of the whole simulated BH-star population. We expect up to $\approx 4000$ BH-star systems in the Galactic halo formed through isolated evolution, of which $\approx 100$ are compatible with Gaia BH3-like. Given the density profile of the Galactic halo we do not expect more than one at the observed distance of Gaia BH3. Our models show that, even if it was born inside a stellar cluster, Gaia BH3 is compatible with a primordial binary star that escaped from its parent cluster without experiencing significant dynamical interactions.

astro-ph.GA↗

arXiv2024

GWnext 2024: Meeting Summary

GWnext 2024 was a meeting held in the Kavli Institute for Astronomy and Astrophysics at Peking University in March $4^\text{th} - 8^\text{th}$, 2024. In the meeting researchers at different career stages -- with a particular focus on early career scientists -- working on the different aspects of gravitational wave (GW) astronomy gathered to discuss the current status as well as prospects of the field. The meeting was divided into three core sessions: Astrophysics, GW Theory, and Detection. Each session consisted of introductory talks and extended discussion sessions. Moreover, there was a poster session where students could present their results. In this paper, we summarize the results presented during the meeting and present the most important outcomes.

astro-ph.HE↗