arXiv subjects

Cailin Plunkett

Publications and source records attributed to Cailin Plunkett.

6 recordsLinked to original sources

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

Measurement prospects for the pair-instability mass cutoff with gravitational waves

Pair-instability supernovae leave behind no compact remnants, resulting in a predicted gap in the distribution of stellar black-hole masses. Gravitational waves from binary black-hole mergers probe the relevant mass range and analyses of the LIGO-Virgo-KAGRA catalog (GWTC-4) indicate a possible mass cutoff at $40$-$50\,M_\odot$. However, the robustness of this result remains unclear. To this end, using full Bayesian parameter estimation, we simulate gravitational-wave catalogs with and without such a mass cutoff, then test whether its presence or absence is correctly inferred with parametric population models. For catalogs similar to GWTC-4, confident identification of a cutoff is not guaranteed, but the best constraints among our simulations are compatible with results from GWTC-4 when the model includes a cutoff. Conversely, spurious identification of a cutoff is unlikely. For catalogs expected by the end of the O4 observing run, uncertainty in the cutoff mass is reduced by $\gtrsim20\,\%$, but a cutoff at 40-50$M_\odot$ yields only a lower bound on the $^{12}\mathrm{C}(\alpha,\gamma)^{16}\mathrm{O}$ reaction rate, our most stringent constraints on the S-factor at $300\,\mathrm{keV}$ being $S_{300}\gtrsim125\,\mathrm{keV}\,\mathrm{b}$ at $90\,\%$ credibility. Relative uncertainties on the Hubble parameter $H_0$ from gravitational-wave data alone can still be up to $100\,\%$. We also analyze GWTC-4 with the nonparametric PixelPop population model, finding that some mass features are more prominent than in parametric models but a sharp cutoff is not required. However, the parametric model passes a likelihood-based predictive test in GWTC-4 and the PixelPop results are consistent with those from our simulated catalogs with a cutoff. Such tests are necessary to make astrophysical claims from gravitational-wave catalogs.

astro-ph.HE↗

arXiv2026

Signatures of a subpopulation of hierarchical mergers in the GWTC-4 gravitational-wave dataset

Repeated black-hole mergers in dense stellar clusters are a plausible mechanism to populate the predicted gap in black hole masses due to the pair-instability supernova process. These hierarchical mergers carry distinct spin characteristics relative to first-generation black holes. We introduce an astrophysically motivated model in the joint space of effective inspiral and precessing spins, which captures the dominant spin dynamics expected for hierarchical mergers. We find decisive evidence for a transition at $m_1 = 46.2_{-7.2}^{+12.6} M_\odot$, above which the population is nearly entirely hierarchical, a location consistent with the anticipated onset of the pair-instability gap. We also infer a global peak in the hierarchical merger rate at $m_1 = 15.7_{-1.1}^{+3.2} M_\odot$. The existence of low- and high-mass subpopulations of higher-generation black holes suggests the contribution of both near-solar-metallicity and metal-poor star clusters to the hierarchical merger population. Our results reinforce the growing evidence for detailed, mass-dependent substructure in the spin distribution of the binary black hole population.

gr-qc↗

arXiv2025

Constraining Population III stellar demographics with next-generation gravitational-wave observatories

Next-generation gravitational-wave observatories will reach farther into the universe than currently possible, revealing black-hole mergers from early stellar binary systems such as Population III stars, whose properties are currently poorly constrained. We develop a method to infer the properties of their progenitor populations from gravitational-wave catalogs. Using Bayesian deep learning, we train an emulator for population-synthesis predictions of black-hole merger properties across redshift as a function of the initial stellar mass function, crucially accounting for systematic uncertainty due to the finite number of training simulations. Combined with a nonparametric model for star formation history, we analyze catalogs containing both Population I/II and III sources simulated with full Bayesian parameter estimation for a detector network of Cosmic Explorer and Einstein Telescope with one year of observing time. We demonstrate our ability to separate these two populations at high redshifts where both make comparable contributions to the black-hole merger rate, excluding a Population III merger rate of zero at nearly 100% credibility. Moreover, we can place meaningful constraints on the Population III progenitor distributions; in particular, we constrain the spectral index of the initial mass function to within roughly +/-0.5 of the true value and the log of the star formation rate density to within ~25% over redshifts 10 to 20. By leveraging astrophysics-informed and astrophysics-agnostic models, we demonstrate the discriminative power of our combined inference approach and highlight the potential of next-generation gravitational-wave observatories to uncover the details of high-redshift stellar populations.

gr-qc↗

arXiv2025

Occurrence rates of accreting companions from a new method for computing emission-line survey sensitivity: application to the H-alpha Giant Accreting Protoplanet Survey

A key scientific goal of exoplanet surveys is to characterize the underlying population of planets in the local galaxy. In particular, the properties of accreting protoplanets can inform the rates and physical processes of planet formation. We develop a novel method to compute sensitivity to protoplanets in emission-line direct-imaging surveys, enabling estimates of protoplanet population properties under various planetary accretion and formation theories. In this work, we specialize to the case of H-alpha and investigate three formation models governing the planetary-mass-to-mass-accretion-rate power law, and two accretion models that describe the scaling between total accretion luminosity and observable H-alphaline luminosity. We apply our method to the results of the Magellan Giant Accreting Protoplanet Survey (GAPlanetS) to place the first constraints on accreting companion occurrence rates in systems with transitional circumstellar disks. We compute the posterior probability for transitional disk systems to host an accreting companion (-7 < log MMdot <-3) within 2 arcseconds (~200 au). Using our two accretion models, we find consistent protoplanet rates, with median and 68% credible intervals of 0.16 (+0.19, -0.10) and 0.22 (+0.26, -0.14) accreting companions per star, respectively. Our technique enables studying protoplanet populations under flexible assumptions about planet formation. This formalism provides the statistical underpinning necessary for protoplanet surveys to discriminate among formation and accretion theories for planets and brown dwarfs.

astro-ph.EP↗

arXiv2022

Concurrent estimation of noise and compact-binary signal parameters in gravitational-wave data

Gravitational-wave parameter estimation for compact binary signals typically relies on sequential estimation of the properties of the detector Gaussian noise and of the binary parameters. This procedure assumes that the noise variance, expressed through its power spectral density, is perfectly known in advance. We assess the impact of this approximation on the estimated parameters by means of an analysis that simultaneously estimates the noise and compact binary parameters, thus allowing us to marginalize over uncertainty in the noise properties. We compare the traditional sequential estimation method and the new full marginalization method using events from the GWTC-3 catalog. We find that the recovered signals and inferred parameters agree to within their statistical measurement uncertainty. At current detector sensitivities, uncertainty about the noise power spectral density is a subdominant effect compared to other sources of uncertainty.

gr-qc↗