arXiv subjects

Claire S. Ye

Publications and source records attributed to Claire S. Ye.

At least 19 recordsLinked to original sources

arXiv2026

Inferring Globular Cluster Initial Mass Function from Stellar Streams

The Gaia mission has provided precise astrometry and spectrophotometry for billions of stars in the Milky Way, enabling the identification and kinematic characterization of stellar streams. These streams, remnants of disrupted globular clusters and dwarf galaxies, have revealed the structure of the Milky Way's dark matter halo. We show that stellar streams also encode information about the initial mass function of globular clusters. We combine cold dark matter simulations that model the evolution and disruption of embedded globular clusters with observations of stellar streams and globular clusters to infer the initial cluster mass function. We find that initially more massive clusters produce more massive streams, but deposit a smaller fraction of their initial mass into those streams. Using stream mass and angular momentum measurements, we recover a declining, power-law-like initial mass function with a slope $α= 1.4\pm0.05$ for streams $\gtrsim 1000\,M_{\odot}$ (with a maximum value of $\sim 1.6$ if we strictly use lower limits of stream mass measurements). This work establishes stellar streams as a novel probe of the early mass distribution of globular clusters.

astro-ph.GA↗

arXiv2026

The diverse outcomes of binary white dwarf mergers and connections to Galactic LISA sources

In the coming decade, the millihertz gravitational wave observatory LISA will provide the best constraints yet on the tens of thousands of close white dwarf binaries in the Milky Way, yielding unprecedented insights into the most abundant class of compact object binaries. Following inspiral via gravitational wave emission, interacting white dwarf binary pairs can lead to a multitude of outcomes, including AM Canum Venaticorum (AM CVn) binaries, R Coronae Borealis stars, young, rapidly-spinning single white dwarfs, (millisecond) magnetars, and a variety of explosive transients, most notably Type Ia supernovae. Current and future electromagnetic observations of these various outcomes coupled with the forthcoming flood of data from LISA place us on the precipice of a significant advance in our understanding of the long-term fate of white dwarf binaries. In this paper, we present a suite of mock catalogs of the Milky Way's white dwarf merger history, created using the population synthesis code $\texttt{COSMIC}$ combined with a metallicity-dependent star formation history from FIRE-2 galaxy simulations. We summarize the various merger outcomes expected (based upon varying white dwarf masses and chemical compositions) and explore ways the rates of these outcomes may vary with model uncertainties pertaining to binary evolution. We publicly release these merger catalogs as a tool for facilitating connections between gravitational wave science and white dwarf binary astrophysics.

astro-ph.SR↗

arXiv2026

Red vs. Blue: How metallicity shapes black hole dynamics and mergers in dense star clusters

Dense star clusters are a well-established environment for the formation of gravitational wave sources through dynamical interactions. Recent LIGO-Virgo-KAGRA (LVK) events such as GW241011 and GW241110 provide some of the best evidence yet for a dynamical origin. However, their relatively low component masses are in tension with predictions from low-metallicity globular cluster models (which typically produce more massive black holes), hinting that these events may have originated in higher-metallicity environments. Here we present a new set of Monte Carlo star cluster simulations with refined coverage in metallicity, focusing specifically on clusters with [Fe/H] $\geq-1$, similar to the ''red'' globular cluster subpopulation observed in most galaxies. We show that metallicity has a significant effect on the mass function of black holes and black hole mergers, the total number of black hole mergers per cluster, black hole retention from natal kicks, the mass segregation time for black-hole-driven cluster dynamics, and the merger delay time distribution. We also show that high-metallicity cluster models produce low-mass hierarchical mergers consistent with the mass ratios and component masses of GW241011 and GW241110, motivating the importance of high-metallicity clusters in the astrophysical interpretation of future LVK catalogs.

astro-ph.GA↗

arXiv2026

The Contribution of Disrupted Dense Star Clusters to Gaia's Compact Object Binaries

We present the first model of the Milky Way's detectable compact object--luminous star binary population from disrupted dense star clusters. We bridge large-scale cosmological star cluster formation with high-resolution dynamical evolution of compact object binaries by mapping the predicted star clusters from the EMP-Pathfinder simulations to $N$-body Cluster Monte Carlo models. We predict that approximately $3\times10^5$ white dwarfs (WDs), $1.5\times10^5$ black holes (BHs), and $1\times10^3$ neutron stars (NSs) in binaries with luminous companions are released to the Galaxy from now-disrupted dense star clusters throughout the history of the Milky Way. Synthetic observations modeled with the gaiamock pipeline reveal that the modeled Gaia DR3 yields are sparse ($\approx 2$ WDs, 0 NS, 0 BHs at 90% credibility), with the majority lying beyond the detection horizon. Gaia DR4 is expected to increase the observational yield of these systems only marginally, as the benefits of an expanded search volume are largely offset by the diminished astrometric and photometric precision of more distant sources ($\approx 14$ WDs, 0 NS, 0 BHs). While the underlying BH binary population is similar to that of WDs, they are detected far less frequently; they tend to pair with lower-mass, dimmer companions and have less temporal coverage of their long orbital periods. For NSs, we suggest that the observed over-representation of metal-poor, halo systems is inconsistent with an origin in disrupted dense star clusters. Instead, the observed Gaia NS population could reflect the accretion history of metal-poor, dwarf galaxies into the Milky Way, isolated binary star evolution, or supernova physics.

astro-ph.GA↗

arXiv2026

Black hole mergers from dense star clusters with realistic binary populations

We present a suite of 24 full-lifetime simulations of dense star clusters with the Cluster Monte Carlo (CMC) code, featuring updated input physics and a realistic distribution of initial binary systems. The latter encompasses a mass-dependent binary fraction, period distribution, and eccentricity distribution based on observations of well-studied stellar populations in the Solar neighborhood and nearby star-forming regions. We predict the cosmic rate, masses, and spins of binary black hole (BBH) mergers formed through dynamical assembly, primordial binary evolution, and hierarchical mergers within dense clusters. As with previous model grids with fewer binaries, dynamically assembled first-generation (1G) mergers dominate the rate of cluster-derived mergers, and the total merger rate is consistent with that inferred from LIGO-Virgo-KAGRA observations as of GWTC-5.0. Our models naturally reproduce key features of the inferred BBH population, including the broken-power-law behavior of the primary BH mass spectrum for $m_1 \gtrsim 20 M_\odot$, the shallower (steeper) slope of the secondary mass spectrum relative to the primary for $m_2 \lesssim 10 M_\odot$ ($m_2 \gtrsim 30 M_\odot$), and the shape of the mass-ratio distribution in the low- and high-mass domains. We predict broad distributions of the spin parameters $χ_{\mathrm{eff}}$ and $χ_{\mathrm{p}}$, consistent with previous studies of dynamical assembly in clusters. The merger rate from primordial binary systems within clusters is a small fraction of the total; however, their merger products are frequently involved in subsequent hierarchical mergers, with the result that the hierarchical merger rate evolves more steeply than the 1G dynamical merger rate with redshift.

astro-ph.GA↗

arXiv2026

Mass Distribution of Binary Black Hole Mergers from Young and Old Dense Star Clusters

Dense star clusters are thought to contribute significantly to the merger rates of stellar-mass binary black holes (BBHs) detected by the LIGO-Virgo-KAGRA collaboration. We combine $N$-body dynamic models of realistic dense star clusters with cluster formation histories to estimate the merger rate distribution as a function of primary mass for merging BBHs formed in these environments. It has been argued that dense star clusters -- most notably old globular clusters -- predominantly produce BBH mergers with primary masses $M_p\approx30\,M_{\odot}$. We show that dense star clusters forming at lower redshifts -- and thus having higher metallicities -- naturally produce lower-mass BBH mergers. We find that cluster BBH mergers span a wide range of primary mass, from about $6\,M_{\odot}$ to above $100\,M_{\odot}$, with a peak near $8\,M_{\odot}$, reproducing the overall merger rate distribution inferred from gravitational wave detections. Our results show that most low-mass BBH mergers (about $95\%$ with $M_p\lesssim 20\,M_{\odot}$) originate in metal-rich ($Z \sim Z_{\odot}$) dense star clusters, while more massive BBH mergers form predominately in metal-poor globular clusters. We also discuss the role of hierarchical mergers in shaping the BBH mass distribution. Gravitational wave detection of dynamically-formed low-mass BBH mergers -- potentially identifiable by features such as isotropic spin distributions -- may serve as probes of cluster formation histories in metal-rich environments at low redshifts.

astro-ph.HE↗

arXiv2026

Is GW231123 a hierarchical merger?

The binary black hole merger GW231123 is both the most massive gravitational-wave event observed and has the highest component spins measured to date. The dimensionless spins of the more massive (primary) and less massive (secondary) black holes are measured to be $χ_1 = 0.90^{+0.10}_{-0.19}$ and $χ_2 = 0.80^{+0.20}_{-0.51}$ ($90\%$ credible intervals), respectively. Its large mass and extremal spins are challenging to explain through standard binary stellar physics, though a flurry of hypothetical scenarios have been proposed. Hierarchical assembly - i.e., mergers of black holes that are themselves formed from previous generations of mergers - is generally a promising way to explain massive and rapidly spinning black holes. Here, we investigate the possibility that GW231123 was assembled hierarchically in a dense star cluster as the merger of two second-generation black holes. Taking the inferred spin values at face value, we find that it is possible ($p\approx 5\%$) that a compact binary with component spins like GW231123 could form in a cluster from hierarchical assembly.

astro-ph.HE↗

arXiv2026

Fast Radio Bursts from White Dwarf Binary Mergers: Isolated and Triple-Induced Channels

The detection of fast radio bursts (FRBs) in both young and old stellar populations suggests multiple formation pathways, beyond just young magnetars from core-collapse supernovae. A promising delayed channel involves the formation of FRB-emitting neutron stars through merger- or accretion-induced collapse of a massive white dwarf (WD). By simulating a realistic stellar population with both binaries and triples, we identify pathways to WD collapse that could produce FRB candidates. We find that (i) triple dynamics open new merger channels inaccessible to isolated binaries, significantly enhancing the overall merger rate; (ii) triple-induced mergers broaden the delay-time distribution, producing long-delay ($\gtrsim1$-8~Gyr) events largely independent of metallicity, alongside a shorter-delay population ($\lesssim100$~Myr) of rapid mergers; (iii) these long delays naturally yield FRBs in older environments such as quiescent host galaxies and galactic halos; (iv) when convolved with the cosmic star-formation history, binary channels track the star-formation rate ($z_{\rm peak} \sim 2$), while triple channels peak later ($z_{\rm peak} \sim 1$), giving a combined local source rate of $R_0 \approx 2\times10^4~{\rm Gpc^{-3}~yr^{-1}}$, consistent with observations; and (v) applying the same framework to Type~Ia supernovae, we find that triples extend the delay-time tail and roughly double the Ia efficiency relative to binaries, yielding rates and redshift evolution in good agreement with observations. If FRBs originate from the collapse of WDs, our results establish triples, alongside binaries, as a crucial and previously overlooked formation pathway whose predicted rates, host demographics, and redshift evolution offer clear tests for upcoming surveys.

astro-ph.HE↗

arXiv2025

Very Massive Stars and High N/O: A Tale of the Nitrogen-enriched Super Star Cluster in the Sunburst Arc

The lensed Sunburst Arc ($z = 2.369$) hosts a young ($\sim2$--$4\,\rm Myr$), massive ($M_\star \sim 10^7\,M_\odot$), compact ($R_{\rm eff} \sim 8\,\rm pc$) Lyman-continuum (LyC) leaking super star cluster, which powers a compact ($< 10\,\rm pc$), high-pressure nebula at sub-solar metallicity $\sim0.2\,Z_\odot$ and with an anomalously elevated nitrogen-to-oxygen ratio $\log({\rm N/O}) \sim -0.2$. We present semi-analytic models and 3D magnetohydrodynamic simulations with radiative feedback in an attempt to reproduce this system. The results indicate that the progenitor giant molecular cloud (GMC) may have $M_{\rm cloud} \gtrsim 3 \times 10^7\,M_\odot$ and $R_{\rm cloud} \sim 70\,\rm pc$, corresponding to a surface density $\sim10^3$--$10^4\,M_\odot\,{\rm pc}^{-2}$. Incorporating feedback from individual Very Massive Stars (VMSs; $\ge 100\,M_\odot$) sampled from the Kroupa initial mass function, we find that their winds rapidly enrich $\sim 10^4\,M_\odot$ of nearby gas with nitrogen ($\sim 1\,$dex) and helium ($\sim 0.1$--$0.2\,$dex). In the first $1$--$3\,$Myr, some cold gas falls to the system center where a central cluster builds up from sub-cluster mergers. There, the gas is photoionized, pressurized, and chemically enriched by the newly formed VMSs, before being radiatively expelled in the next $\sim1\,\rm Myr$. We find that both VMS feedback and a high-surface-density progenitor GMC are necessary to reproduce the observed nebular properties, such as high N/O, high pressure, and stellar proximity. Low metallicity ($Z \le 0.004$) may be essential to avoid overproduction of carbon from WC stars. Such enrichment processes localized to compact starburst events may have caused strong nitrogen emission from dense ionized gas as observed in high-redshift galaxies such as GN-z11 and GS_3073.

astro-ph.GA↗

arXiv2025

Connecting Cores and Black Hole Dynamics Across Scales: From Globular Clusters to Massive Ellipticals

The centers of massive elliptical galaxies exhibit a wide range in density profiles, from central cusps to resolved cores with order kiloparsec sizes. The cored ellipticals have been linked to the presence of supermassive black hole binaries that excavate their hosts' central stellar populations through three-body encounters. This connection between cores and black holes similarly operates in globular clusters, which also exhibit a bimodality in cored and core-collapsed architectures, respectively rich and depleted in stellar black holes. We report new estimates of the total black hole mass in 25 Galactic globular clusters based on a suite of roughly 150 Monte Carlo $N$-body simulations that fit observed surface brightness and velocity dispersion profiles. We show that both globular clusters and massive elliptical galaxies individually exhibit strong correlations between total black hole mass ($M_\bullet$) and core radius ($r_c$), and that these individual relations share a common power-law exponent to within $1σ$ statistical precision: $M_\bullet \sim r_c^{1.3}$. The individual relations appear to be offset, suggesting swarms of stellar black holes scour globular cluster cores more efficiently than lone supermassive black holes scour the cores of massive ellipticals. Yet the shared basis of core scouring via black hole binaries hints at a unified $M_{\bullet}-r_c$ connection across over 10 orders of magnitude in $M_\bullet$. Our findings imply core radius measurements may offer a powerful observational constraint on black hole merger rates, from kilohertz sources detectable by LIGO/Virgo/KAGRA formed in globular clusters to millihertz and nanohertz sources formed in massive elliptical galaxies.

astro-ph.GA↗

arXiv2025

The ejection and detectability of high- and hyper-velocity stars by compact object binaries in globular clusters

The dense cores of Milky Way globular clusters (GCs) play host to a variety of dynamical encounters between stellar objects, which can accelerate stars to velocities high enough to escape the GC. The most extreme examples of these encounters are interactions between single GC stars and binaries including at least one compact object. These interactions can result in ejection velocities of up to several hundred $\mathrm{km \ s^{-1}}$, approaching or even exceeding the escape velocity of the Galaxy itself. In order to study whether these interactions contribute to the Galactic population of hypervelocity stars (stars moving faster than the Galactic escape speed), we combine Monte Carlo $N$-body GC simulations, observations of Galactic GCs, and a particle spray code to generate realistic populations of stars which have escaped from Milky Way GCs following star + compact object binary (S+COB) interactions. We find that over the last 500 Myr, S+COB interactions have likely ejected $\sim$6300 stars from Galactic GCs, of which $839_{-67}^{+70}$ have present-day velocities exceeding $500 \; \mathrm{km \ s^{-1}}$. Using mock photometric observations, we find that $290_{-23}^{+28}$ ejected stars are detectable in Gaia Data Release 3, however, only $1_{-1}^{+2}$ stars faster than $500 \; \mathrm{km \ s^{-1}}$ are detectable. Even so, we show that observational prospects in the upcoming Legacy Survey of Space and Time are more optimistic, and future detected fast extratidal GC stars will serve as a useful probe of GC cores.

astro-ph.GA↗

arXiv2025

Can slow pulsars in Milky Way globular clusters form via partial recycling?

Alongside the population of several hundred radio millisecond pulsars currently known in Milky Way globular clusters, a subset of six slowly spinning pulsars (spin periods $0.3-4\,$s) are also observed. With inferred magnetic fields $\gtrsim 10^{11}\,$G and characteristic ages $\lesssim10^8\,$yr, explaining the formation of these apparently young pulsars in old stellar populations poses a major challenge. One popular explanation is that these objects are not actually young but instead have been partially spun up via accretion from a binary companion. In this scenario, accretion in a typical low-mass X-ray binary is interrupted by a dynamical encounter with a neighboring object in the cluster. Instead of complete spin up to millisecond spin periods, the accretion is halted prematurely, leaving behind a ''partially recycled'' neutron star. In this Letter, we use a combination of analytic arguments motivated by low-mass X-ray binary evolution and $N$-body simulations to show that this partial-recycling mechanism is not viable. Realistic globular clusters are not sufficiently dense to interrupt mass transfer on the short timescales required to achieve such slow spin periods. We argue that collapse of massive white dwarfs and/or neutron star collisions are more promising ways to form slow pulsars in old globular clusters.

astro-ph.SR↗

arXiv2025

Gravitational-wave kicks impact spins of black holes from hierarchical mergers

One proposed black hole formation channel involves hierarchical mergers, where black holes form through repeated binary mergers. Previous studies have shown that such black holes follow a near-universal spin distribution centered around 0.7. However, gravitational-wave kicks can eject remnants from their host environments, meaning only retained black holes can participate in subsequent mergers. We calculate the spin distribution of retained black holes in typical globular clusters, accounting for remnant kick velocities. Since the kick magnitude depends on the binary's mass ratio and spin orientations, certain configurations are more likely to be retained than others. This preferentially selects certain remnant spin magnitudes, skewing the spin distribution of second-generation black holes away from the universal distribution. In low escape velocity environments, the distribution can become bimodal, as remnants with spins of 0.7 typically receive larger kicks than other configurations. Regarding higher-generation black holes, their spin distribution does not converge to a unique form, and can span a broad range of spins, $a_f \in (0.4,1)$, depending on their merger history, birth spins and the escape velocity. Additionally, we find that the presence of a small fraction of binaries with near-aligned spins can produce a second, more dominant peak, whose position depends on the birth spin magnitude. Our findings identify observable features of hierarchical merger black holes, which is essential for understanding their contribution to the gravitational-wave population. Moreover, the dependence of the spin distribution on astrophysical parameters means that precise spin measurements could provide insights into their formation environments.

astro-ph.HE↗

arXiv2025

Predicting the rate of fast radio bursts in globular clusters from binary black hole observations

The repeating fast radio burst (FRB) source in an old globular cluster (GC) in M81 proves that FRBs, which are typically associated with young magnetars, can also occur in old stellar populations. A potential explanation is super-Chandrasekhar binary white dwarf (BWD) coalescences, which may produce FRB-emitting neutron stars. GCs can also give rise to binary black hole (BBH) mergers detectable with gravitational waves, and the BWD coalescence rate from GCs is correlated with their BBH merger rate. For the first time, we combine independent observations of gravitational waves and FRBs to infer the origins of FRB sources. We use GC formation histories inferred from BBH observations to predict the rate of super-Chandrasekhar BWD coalescences originating from GCs as a function of redshift. We explore mass-loss and mass-conserved scenarios for BWD coalescences and find that the coalescence rates evolve differently across redshift in these two cases. In the mass-loss scenario, the BWD coalescence rates decrease with increasing redshift, similar to some recent measurements of the FRB rate as a function of redshift. We show that GCs could contribute $\lesssim 1\%$ to the total FRB source formation rates in the local Universe. Our multi-messenger approach also offers a novel method to better constrain the GC population using both FRB and gravitational wave observations.

astro-ph.HE↗

arXiv2025

Investigating cannibalistic millisecond pulsar binaries using MESA: New constraints from pulsar spin and mass evolution

Compact binary millisecond pulsars (MSPs) with orbital periods $\lesssim1$d are key to understanding binary evolution involving massive neutron stars (NSs). Due to the ablation of the companion by the rapidly spinning pulsar, these systems are also known as spiders and categorized into two main branches: redbacks (RBs; companion mass in the range of 0.1 to 0.5\,\Msun) and black widows (BWs; companion mass $\lesssim$\,0.1\,\Msun). We present models of low- and intermediate-mass X-ray binaries and compare them with observations of Galactic spiders (including the presence or absence of hydrogen lines in their optical spectra), and we constrain and quantify the interaction between the pulsar and the companion. Using MESA, we created the allowed initial parameter space. For the first time in MESA, we also included the detailed evolution of the pulsar spin and modeled the irradiation of the companion by the pulsar wind. Efficient mass accretion onto the NS (at least $70\%$ of the mass transferred is accreted) with an X-ray irradiated disk followed by strong irradiation of the companion can explain most of the properties of the observed spiders. Our RB evolutionary tracks continue to the BW regime, connecting the two branches of spiders. Our models explain the lack of hydrogen in some observed BWs with ultra-light companions. During accretion induced spin up, the mass required to spin up an NS to sub-milliseconds is high enough to collapse it into a black hole. Finally, after analyzing the formation of RB-like spiders with giant companions and orbital periods of several days (huntsmen), we conclude that they are unlikely to produce super-massive NSs (maximum accreted mass $\lesssim$0.5M$_{\odot}$). Cannibalistic MSP binary formation depends heavily on the interplay between accretion onto the pulsar and pulsar wind irradiation.

astro-ph.HE↗

arXiv2024

Binary properties of the globular cluster 47 Tuc (NGC 104). A dearth of short-period binaries

Spectroscopic observations of binary stars in globular clusters are essential to shed light on the poorly constrained period, eccentricity, and mass ratio distributions and to develop an understanding of the formation of peculiar stellar objects. 47 Tuc (NGC 104) is one of the most massive Galactic globular clusters, with a large population of blue stragglers and with many predicted but as-yet elusive stellar-mass black holes. This makes it an exciting candidate for binary searches. We present a multi-epoch spectroscopic survey of 47 Tuc with the VLT/MUSE integral field spectrograph to determine radial velocity variations for 21,699 stars. We find a total binary fraction in the cluster of $(2.4\pm1.0)\%$, consistent with previous photometric estimates, and an increased binary fraction among blue straggler stars, approximately three times higher than the cluster average. We find very few binaries with periods below three days, and none with massive dark companions. A comparison with predictions from state-of-the-art models shows that the absence of such short-period binaries and of binaries with massive companions is surprising, highlighting the need to improve our understanding of stellar and dynamical evolution in binary systems.

astro-ph.SR↗

arXiv2024

Lower-mass-gap Black Holes in Dense Star Clusters

The existence of compact stellar remnants in the mass range $2-5\,M_{\odot}$ has long been debated. This so-called lower mass gap was initially suggested by the lack of low-mass X-ray binary observations with accretors about $2-5\,M_{\odot}$, but it has recently been called into question following newer observations, including a lower-mass-gap candidate with a millisecond pulsar companion in the dense globular cluster NGC 1851. Here we model NGC 1851 with a grid of similar dense star clusters utilizing the state-of-the-art Monte Carlo $N$-body code \texttt{CMC}, and we specifically study the formation of lower-mass-gap black holes. We demonstrate that both massive star evolution and dynamical interactions can contribute to forming lower-mass-gap black holes. In general, the collapse of massive remnants formed through mergers of neutron stars or massive white dwarfs produces the largest number of lower-mass-gap black holes among all formation channels. However, in more massive clusters, supernova core collapse can contribute comparable numbers. Our NGC 1851-like models can reproduce millisecond pulsar -- lower-mass-gap black hole binaries similar to the observed system. Additionally, the lower-mass-gap black holes can also become components of dynamically assembled binaries, and some will be in merging black hole - neutron star systems similar to the recently detected gravitational wave source GW230529. However, the corresponding merger rate is probably $\lesssim 1~{\rm Gpc^{-3}\,yr^{-1}}$.

astro-ph.HE↗

arXiv2024

The Redshift Evolution of the Binary Black Hole Mass Distribution from Dense Star Clusters

Gravitational-wave detectors are unveiling a population of binary black hole (BBH) mergers out to redshifts $z \approx 1$, and are starting to constrain how the BBH population evolves with redshift. We present predictions for the redshift evolution of the BBH mass and spin distributions for systems originating from dense star clusters. Utilizing a grid of 144 state-of-the-art dynamical models for globular clusters, we demonstrate that BBH merger rates peak at higher redshifts for larger black hole primary masses $M_1$. Specifically, for $M_1\gtrsim40\,M_{\odot}$, the BBH merger rate reaches its peak at redshift $z\approx2.1$, while for $M_1\lesssim20\,M_{\odot}$, the peak occurs at $z\approx1.1$, assuming that the cluster formation rate peaks at $z=2.2$. The average BBH primary mass also increases from $\sim 10\,M_{\odot}$ at $z=0$ to $\sim 30\,M_{\odot}$ at $z=10$. We show that $\sim 20\%$ BBHs contain massive remnants from next-generation mergers, with this fraction increasing (decreasing) for larger (smaller) primary masses. This difference is not large enough to significantly alter the effective spins of the BBH population originating from globular clusters, and we find that their effective spin distribution does not evolve across cosmic time. These findings can be used to distinguish BBHs from dense star clusters by future gravitational wave observations.

astro-ph.HE↗