arXiv subjects

Aryanna Schiebelbein-Zwack

Publications and source records attributed to Aryanna Schiebelbein-Zwack.

5 recordsLinked to original sources

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

Regression on Regression: Mapping Data-Driven Binary Black Hole Merger Rate Fits to Progenitor Histories

The binary black hole (BBH) merger rate is governed by the progenitor formation rate and the distribution of delay-times between formation and merger, but these functions remain poorly constrained. We introduce a framework that maps the parameters of physics-driven models directly onto existing data-driven fits of the BBH merger rate. This ``regression on regression'' approach enables physical interpretation of flexible population models without the computational burden of reanalyzing the underlying gravitational-wave event data. Applying this method to the \textsc{B-Spline} merger-rate posteriors from the Fourth Gravitational-Wave Transient Catalog, we fit the minimum delay time ($τ_{\text{min}}$), delay-time power-law index ($α$), and progenitor formation parameters controlling the normalization ($\mathcal{A}$), early-time growth ($γ$), and late-time decay ($δ$). Increasing the number of anchoring redshift points from two to four reduces the median sum-squared error (SSE) by a factor of $\approx 4.5$. However, residuals reveal that the physical model does not pass through all four anchors, exposing model misspecification and demonstrating a key strength of the framework: unlike standard inference methods, which preferentially weight compatible curves and mask underlying tensions, our approach exposes BBH posteriors irreconcilable with the model. Despite uncertainties at $z\gtrsim1$, the shape of the progenitor formation rate at low-$z$ is robust and evolves more steeply than the global star formation rate (SFR), supporting a preference for low metallicity environments. Specifically, the log-space slope of the progenitor rate is $\approx 5.3$ times steeper than the SFR between $z=0.1$ and $z=1.0$. Ultimately, a more complex phenomenological model is required to match the \textsc{B-Spline} merger rates.

astro-ph.HE↗

arXiv2026

Forbidden Formation Histories: The Binary Black Hole Merger Rate Disfavors Long Delay Times

The redshift evolution of the binary black hole (BBH) merger rate can be expressed as the convolution of the progenitor formation rate with the distribution of time delays between formation and merger. We show that starting with data-driven fits to the BBH merger rate as a function of redshift, deconvolving the inferred BBH merger rate into a delay time distribution and progenitor formation rate exposes physically incompatible delay time distributions. For a given evolution of the merger rate, certain delay time distributions are forbidden because their long-delay tails overpredict low redshift mergers independently of any assumption about the progenitor formation rate. Using delay-time distributions derived from the COMPAS population synthesis code in combination with the BBH merger rate inferred from GWTC-4.0, we reconstruct the physically permitted progenitor formation histories and find a steeper decline toward low redshift than the global star formation rate. We also find that the GWTC-4.0 data are in tension with formation channels that predict shallow power-law delay-time distributions ($α\gtrsim -0.7$), such as stable mass transfer. Conversely, imposing the COMPAS predictions for the delay time distribution as a prior reduces the median merger rate inferred in GWTC-4.0 by 10% at $z=1.5$, favoring a shallower merger rate evolution than the standard GWTC-4.0 inference. Additionally, we demonstrate that our method can constrain binary evolution physics by directly evaluating the compatibility of population synthesis parameters with gravitational wave observations. Our framework provides a model-independent avenue for ruling out regions of binary evolution and merger rate parameter space.

astro-ph.HE↗

arXiv2025

Surprisingly Similar: The Mass Function of Gaia Neutron Stars and First-Born Double Neutron Stars

The mass distribution of neutron stars encodes information about their formation and binary evolution. We compare the masses of two distinct populations: I) the recently identified Gaia neutron stars in wide orbits with solar-like companions and, II) the assumed first-born recycled pulsar in Galactic double neutron star systems. Naively, one would expect their masses to differ due to both the presumed differences in their evolutionary histories, as well as astrophysical selection effects that can filter out configurations that would merge or be disrupted. Yet, we find that their mass distributions are strikingly similar. Using a two-component Gaussian model, we find that both populations exhibit a narrow component centred near $1.3 \text{ M}_\odot$, accompanied by a broader, higher-mass component that extends the distribution toward larger masses. The highest density regions of their fitted parameter posteriors coincide by over 91.6%. Statistical tests further confirm the agreement between these distributions with a Jensen-Shannon divergence $JS < 0.08$ and an earth mover's distance of $W <0.063 \text{ M}_\odot$ at 90% credibility. This finding seems to imply that both mass functions reflect the natal mass distribution of first-born neutron stars in binary systems, supporting the hypothesis that neutron stars can be born with high masses. Consequently and perhaps surprisingly, binary evolutionary processes need not impart features on the NS mass distribution.

astro-ph.SR↗

arXiv2024

The Mass Density of Merging Binary Black Holes Over Cosmic Time

The connection between the binary black hole (BBH) mergers observed by LIGO-Virgo-KAGRA (LVK) and their stellar progenitors remains uncertain. Specifically, the fraction $ε$ of stellar mass that ends up in BBH mergers and the delay time $τ$ between star formation and BBH merger carry information about the astrophysical processes that give rise to merging BBHs. We model the BBH merger rate in terms of the cosmic star formation history, coupled with a metallicity-dependent efficiency $ε$ and a distribution of delay times $τ$, and infer these parameters with data from the Third Gravitational-Wave Transient Catalog (GWTC-3). We find that the progenitors to merging BBHs preferentially form in low metallicity environments with a low metallicity efficiency of $\log_{10}ε_{ 10\,M_\odot$) progenitors. However, because massive stars are so short-lived, there may be more mass in merging BBHs than in living massive stars as early as $\sim 2.5$ Gyr ago. We also compare to the mass in supermassive BHs, finding that the mass densities were comparable $\sim 12.5$ Gyr ago, but the mass density in SMBHs quickly increased to $\sim 75$ times the mass density in merging stellar mass BBHs by $z\sim 1$.

astro-ph.HE↗