arXiv subjects

Nathan Steinle

Publications and source records attributed to Nathan Steinle.

17 recordsLinked to original sources

arXiv2026

A new model for the continuum spectra of AM CVn binaries and multi-messenger inference with normalizing flows

Future electromagnetic telescopes, such as $\textit{NewAthena}$, $\textit{CASTOR}$, and an $\textit{AXIS}$-like mission, along with milli-Hz gravitational-wave (GW) detectors such as $\textit{LISA}$, are expected to unearth the population of Galactic ultra-compact binaries (UCBs). Joint multi-messenger detections will probe the uncertain formation, evolution, and observables of mass-transferring UCBs such as AM CVns, but theoretical tools need to be advanced to anticipate future data challenges. Motivated by this, we present a new forward model for the continuum emission of AM CVn binaries that connects source binary parameters to X-ray, optical, and ultraviolet observables. The model assumes GW-driven mass transfer with physically motivated prescriptions for accretion energetics, emission geometry, absorption, and instrumental response. Combining this with $\textit{LISA}$ observations and the output of binary population synthesis enables exploration of the multi-messenger properties of AM CVns. Although uncertain, our model predicts that approximately one per $7000$ AM CVn binaries will permit a joint multi-messenger detection with $\textit{LISA}$, $\textit{CASTOR}$, and $\textit{AXIS}$. We also develop a framework for inferring binary parameters from the inverse model with a convolutional neural net and normalizing flows. Testing the trained flow with our synthetic AM CVn population, we find mean absolute fractional error on the inferred accretor mass of $0.05$ M$_{\odot}$, donor mass of $0.26$ M$_{\odot}$, orbital period of $0.1$ s, and distance of $0.2$ pc, while Spearman's rank shows strongly correlated true and predicted distributions except for the donor mass. These efforts lay a foundation for follow-up studies that will explore detailed binary astrophysics and observational requirements for effective multi-messenger scientific discovery in the coming decade.

astro-ph.HE↗

arXiv2025

Simulation-calibrated Bayesian inference for progenitor properties of the microquasar SS 433

SS$\,$433 is one of the most extreme Galactic X-ray binaries, launching semi-relativistic jets and showing clear signs of super-critical accretion onto what is likely a black hole. Yet the properties of the binary system that produced it remain uncertain. To solve the inverse problem of inferring the progenitor properties of binaries that evolve into SS$\,$433-like systems, we use an iterative, simulation-based calibration framework that combines Bayesian inference with the isolated binary-evolution code COSMIC. Using six measured properties of SS$\,$433 and the dynamic nested sampler $\texttt{dynesty}$, we explore a ten-dimensional space of possible progenitor masses, orbits, mass-transfer histories, and natal-kick velocities. This approach identifies the regions of parameter space most consistent with SS$\,$433 and allows us to iteratively refine the resulting progenitor distributions. We find 90% confidence intervals for the progenitor initial primary mass of (8, 11) M$_\odot$, secondary mass of (32, 40) M$_\odot$, orbital period of (136, 2259) days, eccentricity of (0.26, 0.6), common-envelope efficiency of (0.44, 0.76), accreted fraction during stable mass transfer of (0.22, 0.6), and black-hole natal-kick magnitude of (5, 68) km/s. These results show that direct probabilistic inference of X-ray binary progenitors can yield new constraints on the formation of extreme accretion systems like SS$\,$433, which has important implications for theoretical expectations of the population of SS$\,$433-like systems in the Galaxy and their connection with cosmic ray observations.

astro-ph.HE↗

arXiv2025

Detecting regular precession using a new gravitational waveform model directly parameterized by both precession amplitude and frequency

Nearly 210 binary black hole (BBH) mergers have been observed by the LIGO-Virgo-KAGRA network during its four observing runs. Generic BBHs are spinning, and their spins are misaligned with the orbital angular momentum $\vec{L}$. These misaligned spins cause $\vec{L}$ to precess in a cone with dimensionless precession amplitude $\tilde{\theta}$ and frequency $\tilde{\Omega}$ about the nearly constant direction of the total angular momentum. This precession modulates the observed GWs. We propose a model of regularly precessing (RP) waveforms that incorporates $\tilde{\theta}$ and $\tilde{\Omega}$ directly as parameters. We investigate how these waveforms vary as functions of these precessional parameters, as well as binary orientation and sky location. We use the Lindblom criterion to estimate that precession can be detected in a RP source with signal-to-noise ratio $\rho$ when the mismatch $\epsilon$ with a non-precessing (NP) source with otherwise identical parameters exceeds $1/2\rho^2$. Precession is most detectable when $\vec{L}$ precesses through configurations we call +~nulls during the inspiral. At +~nulls, a NP source only emits +-polarization to which the GW detector is insensitive. The large mismatch between a RP source and this vanishing NP signal enhances the detectability of precession. We also explore the detectability of precession as a function of redshift $z$ for different BBH populations. We find that for BBHs with isotropically oriented maximal spins, precession is detectable in a majority of systems out to $z \approx 0.3$ for chirp masses $10 \lesssim M_c/M_\odot \lesssim 40$ and mass ratios $q \gtrsim 0.5$. Reduced spin magnitudes or greater alignment between the spins and $\vec{L}$ make it difficult to observe beyond $z \approx 0.1$. (abridged)

gr-qc↗

arXiv2025

Machine learning classification of black holes in the mass--spin diagram

We present the mass--spin diagram for classifying black holes and studying their formation pathways providing an analogue to the Hertzsprung-Russell diagram. This allows for black hole evolutionary tracks as a function of redshift, combining formation, accretion, and merger histories for the variety of black hole populations. A realistic black hole continuum constructed from initial mass and spin functions and approximate redshift evolution reveals possible black hole main sequences, such as sustained coherent accretion through cosmic time or hierarchical merger trees. In the stellar-mass regime, we use a binary population synthesis software to compare three spin prescriptions for tidal evolution of Wolf-Rayet progenitors, showing how the mass--spin diagram exposes interesting modeling differences. We then classify black hole populations by applying supervised and unsupervised machine learning clustering methods to mass--spin datasets. While bare unsupervised clustering can nearly recover canonical population boundaries (stellar-mass, intermediate-mass, and supermassive), a more sophisticated approach utilizing deep learning via variational autoencoders for latent space representation learning aids in clustering of realistic datasets with subclasses that highly overlap in mass--spin space. We find that a supervised random forest can accurately recover the correct clusters from the learned latent space representation depending on the complexity of the underlying dataset, semi-supervised methods show potential for further development, and the performance of unsupervised classifiers is a great challenge. Our findings motivate future machine learning applications and demonstrate that the mass--spin diagram can be used to connect gravitational-wave and electromagnetic observations with theoretical models.

astro-ph.HE↗

arXiv2025

Compact Binary Coalescence Sensitivity Estimates with Injection Campaigns during the LIGO-Virgo-KAGRA Collaborations' Fourth Observing Run

We describe the effort to characterize gravitational-wave searches and detector sensitivity to different types of compact binary coalescences during the LIGO-Virgo-KAGRA Collaborations' fourth observing run. We discuss the design requirements and example use cases for this data product, constructed from $> 4.33\times10^8$ injections during O4a alone. We also identify subtle effects with high confidence, like diurnal duty cycles within detectors. This paper accompanies a public data release of the curated injection set, and the appendixes give detailed examples of how to use the publicly available data.

gr-qc↗

arXiv2025

Binary Neutron Star Mergers: Multi-Messenger Systematics and Prospects with Next-Generation Facilities

Multi-messenger astronomy was galvanized by the detection of gravitational waves (GWs) from the binary neutron star (BNS) merger GW170817 and electromagnetic (EM) emission from the subsequent kilonova and short gamma ray burst. Maximizing multi-messenger constraints on these systems requires combining models of the progenitors and products of BNS mergers within a single framework. Motivated by GW170817, we create a combined model that relate the progenitor astrophysics of a BNS population with their GW observability and localizability, kilonova light curves, gamma-ray burst afterglow flux, and kilonova remnant evolution. We compute the BNS merger rate by convolving metallicity-dependent star-formation history with population-synthesis predictions, and we sample realistic populations to evaluate their GW and EM observables and joint detection rates. We find that next-generation detectors will typically observe BNS mergers with GW network signal-to-noise ratios of $\sim$ 10 to 20, 90th-percentile sky areas of order $\sim$ 10 deg$^2$, and kilonova $i$-band magnitudes spanning $\sim$ 23 to 33. The variation of the merger rate with respect to the common-envelope efficiency is shown in the GW and EM observables and the resulting multi-messenger detection yield, demonstrating how uncertainties propagate into all stages of joint GW+EM forecasting. Across the models examined, no more than $\sim$ 4% of BNS mergers are detectable simultaneously by a two-Cosmic-Explorer plus one-Einstein-Telescope network and by both Roman (in a $K$-like band) and Rubin ($i$ and $g$ bands). These results show that assumptions underlying the combination of progenitor evolution and source observables will constitute key multi-messenger modeling systematics for inference of astrophysical, nuclear, and fundamental physics from future datasets.

astro-ph.HE↗

arXiv2025

A multi-messenger window into galactic magnetic fields and black hole mergers with LISA

Large-scale (i.e., $\gtrsim {\rm kpc}$) and micro-Gauss scale magnetic fields have been observed throughout the Milky Way and nearby galaxies. These fields depend on the geometry and matter-energy composition, can display complicated behavior such as direction reversals, and are intimately related to the evolution of the source galaxy. Simultaneously, gravitational-wave astronomy offers a new probe into astrophysical systems, for example the Laser Interferometer Space Antenna (LISA) will observe the mergers of massive (i.e., $M ~> 10^6$ M$_{\odot}$) black-hole binaries and provide extraordinary constraints on the evolution of their galactic hosts. In this work, we show how galactic, large-scale magnetic fields and their electromagnetic signatures are connected with LISA gravitational-wave observations via their common dependence on the massive black-hole binary formation scenario of hierarchical galaxy mergers. Combining existing codes, we astrophysically evolve a population of massive binaries from formation to merger and find that they are detectable by LISA with signal-to-noise ratio $\sim 10^3$ which is correlated with quantities from the progenitors' phase of circumbinary disk migration such as the maximum magnetic field magnitude $|\mathbf{B}| \approx 7 \,\mu$G, polarized intensity, and Faraday rotation measure. Interesting correlations result between these observables arising from their dependencies on the black-hole binary total mass, suggesting a need for further analyses of the full parameter space. We conclude with a discussion on this new multi-messenger window into galactic magnetic fields.

astro-ph.HE↗

arXiv2024

Probing AGN jet precession with LISA

The precession of astrophysical jets produced by active-galactic nuclei is likely related to the dynamics of the accretion disks surrounding the central supermassive black holes (BHs) from which jets are launched. The two main mechanisms that can drive jet precession arise from Lense-Thirring precession and tidal torquing. These can explain direct and indirect observations of precessing jets; however, such explanations often utilize crude approximations of the disk evolution and observing jet precession can be challenging with electromagnetic facilities. Simultaneously, the Laser Interferometer Space Antenna (LISA) is expected to measure gravitational waves from the mergers of massive binary BHs with high accuracy and probe their progenitor evolution. In this paper, we connect the LISA detectability of binary BH mergers to the possible jet precession during their progenitor evolution. We make use of a semi-analytic model that self-consistently treats disk-driven BH alignment and binary inspiral and includes the possibility of disk breaking. We find that tidal torquing of the accretion disk provides a wide range of jet precession timescales depending on the binary separation and the spin direction of the BH from which the jet is launched. Efficient disk-driven BH alignment results in shorter timescales of $\sim 1$ yr which are correlated with higher LISA signal-to-noise ratios. Disk breaking results in the longest possible times of $\sim 10^7$ yrs, suggesting a deep interplay between the disk critical obliquity (i.e. where the disk breaks) and jet precession. Studies such as ours will help to reveal the cosmic population of precessing jets that are detectable with gravitational waves.

astro-ph.HE↗

arXiv2023

Implications of pulsar timing array observations for LISA detections of massive black hole binaries

Pulsar timing arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) will open complementary observational windows on massive black-hole binaries (MBHBs), i.e., with masses in the range $\sim 10^6 - 10^{10}\,$ M$_{\odot}$. While PTAs may detect a stochastic gravitational-wave background from a population of MBHBs, during operation LISA will detect individual merging MBHBs. To demonstrate the profound interplay between LISA and PTAs, we estimate the number of MBHB mergers that one can expect to observe with LISA by extrapolating direct observational constraints on the MBHB merger rate inferred from PTA data. For this, we postulate that the common signal observed by PTAs (and consistent with the increased evidence recently reported) is an astrophysical background sourced by a single MBHB population. We then constrain the LISA detection rate, $\mathcal{R}$, in the mass-redshift space by combining our Bayesian-inferred merger rate with LISA's sensitivity to spin-aligned, inspiral-merger-ringdown waveforms. Using an astrophysically-informed formation model, we predict a 95$\%$ upper limit on the detection rate of $\mathcal{R} < 134\,{\rm yr}^{-1}$ for binaries with total masses in the range $10^7 - 10^8\,$ M$_{\odot}$. For higher masses, i.e., $>10^8\,$ M$_{\odot}$, we find $\mathcal{R} < 2\,(1)\,\mathrm{yr}^{-1}$ using an astrophysically-informed (agnostic) formation model, rising to $11\,(6)\,\mathrm{yr}^{-1}$ if the LISA sensitivity bandwidth extends down to $10^{-5}$ Hz. Forecasts of LISA science potential with PTA background measurements should improve as PTAs continue their search.

astro-ph.HE↗

arXiv2023

Constraining black-hole binary spin precession and nutation with sequential prior conditioning

We investigate the detectability of sub-dominant spin effects in merging black-hole binaries using current gravitational-wave data. Using a phenomenological model that separates the spin dynamics into precession (azimuthal motion) and nutation (polar motion), we present constraints on the resulting amplitudes and frequencies. We also explore current constraints on the spin morphologies, indicating if binaries are trapped near spin-orbit resonances. We dissect such weak effects from the signals using a sequential prior conditioning approach, where parameters are progressively re-sampled from their posterior distribution. This allows us to investigate whether the data contain additional information beyond what is already provided by quantities that are better measured, namely the masses and the effective spin. For the current catalog of events, we find no significant measurements of weak spin effects such as nutation and spin-orbit locking. We synthesize a source with a high nutational amplitude and show that near-future detections will allow us to place powerful constraints, hinting that we may be at the cusp of detecting spin nutations in gravitational-wave data.

gr-qc↗

arXiv2023

Mechanisms for high spin in black-hole neutron-star binaries and kilonova emission: inheritance and accretion

A black-hole neutron-star binary merger can lead to an electromagnetic counterpart called a kilonova if the neutron star is disrupted prior to merger. The observability of a kilonova depends on the amount of neutron star ejecta, which is sensitive to the aligned component of the black hole spin. We explore the dependence of the ejected mass on two main mechanisms that provide high black hole spin in isolated stellar binaries. When the black hole inherits a high spin from a Wolf-Rayet star that was born with least $\sim$ 10% of its breakup spin under weak stellar core-envelope coupling, relevant for all formation pathways, the median of the ejected mass is $\gtrsim$ $10^{-2}$ M$_{\odot}$. Though only possible for certain formation pathways, similar ejected mass results when the black hole accretes $\gtrsim$ 20% of its companion's envelope to gain a high spin. Together, these signatures suggest that a population analysis of black-hole neutron-star binary mergers with observed kilonovae may help distinguish between mechanisms for spin and possible formation pathways. We show that these kilonovae will be difficult to detect with current capabilities, but that future facilities, such as the Vera Rubin Observatory, can do so even if the aligned dimensionless spin of the black hole is as low as $\sim$ 0.2. Our model predicts kilonovae as bright as $M_i$ $\sim$ -14.5 for an aligned black hole spin of $\sim$ 0.9 and mass ratio Q = 3.6.

astro-ph.HE↗

arXiv2023

The Bardeen-Petterson effect, disk breaking, and the spin orientations of supermassive black-hole binaries

Supermassive black-hole binaries are driven to merger by dynamical friction, loss-cone scattering of individual stars, disk migration, and gravitational-wave emission. Two main formation scenarios are expected. Binaries that form in gas-poor galactic environments do not experience disk migration and likely enter the gravitational-wave dominated phase with roughly isotropic spin orientations. Comparatively, binaries that evolve in gas-rich galactic environments might experience prominent phases of disk accretion, where the Bardeen-Petterson effect acts to align the spins of the black holes with the orbital angular momentum of the disk. However, if the accretion disk breaks alignment is expected to be strongly suppressed -- a phenomenon that was recently shown to occur in a large portion of the parameter space. In this paper, we develop a semi-analytic model of joint gas-driven migration and spin alignment of supermassive black-hole binaries taking into account the impact of disk breaking for the first time. Our model predicts the occurrence of distinct subpopulations of binaries depending on the efficiency of spin alignment. This implies that future gravitational-wave observations of merging black holes could potentially be used to (i) discriminate between gas-rich and gas-poor hosts and (ii) constrain the dynamics of warped accretion disks.

astro-ph.HE↗

arXiv2023

Pathways for producing binary black holes with large misaligned spins in the isolated formation channel

Binary black holes (BBHs) can form from the collapsed cores of isolated high-mass binary stars. The masses and spins of these BBHs are determined by the complicated interplay of phenomena such as tides, winds, accretion, common-envelope evolution (CEE), supernova natal kicks, and stellar core-envelope coupling. The gravitational waves emitted during the mergers of BBHs depend on their masses and spins and can thus constrain these phenomena. We present a simplified model of binary stellar evolution and identify regions of the parameter space that produce BBHs with large spins misaligned with their orbital angular momentum. In Scenario A (B) of our model, stable mass transfer (SMT) occurs after Roche-lobe overflow (RLOF) of the more (less) massive star, while CEE follows RLOF of the less (more) massive star. Each scenario is further divided into Pathways 1 and 2 depending on whether the core of the more massive star collapses before or after RLOF of the less massive star, respectively. If the stellar cores are coupled weakly to their envelopes, highly spinning BBHs can be produced if natal spins greater than $10\%$ of the breakup value are inherited from the stellar progenitors. BBHs can alternatively acquire large spins by tidal synchronization during the Wolf-Rayet stage in Scenario A or by accretion onto the initially more massive star during SMT in Scenario B. BBH spins can be highly misaligned if the kicks are comparable to the orbital velocity, which is more easily achieved in Pathway A1 where the kick of the more massive star precedes CEE.

astro-ph.HE↗

arXiv2023

Signatures of spin precession and nutation in isolated black-hole binaries

The spin precession of binary black holes (BBHs) that originate from isolated high-mass binary stars is determined by the interplay of phenomena such as tides, winds, accretion, common-envelope evolution, natal kicks, and stellar core-envelope coupling. In previous work, we identified regions of the parameter space that may produce BBHs with large misalignments from natal kicks and high spin magnitudes from three mechanisms - tides, accretion, or inheritance via minimal core-envelope coupling. Here, we explore the spin precession of such BBHs using five parameters that describe the amplitude and frequency with which the orbital angular momentum precesses and nutates about the total angular momentum, modulating the gravitational-wave emission. Precession is generally possible for sufficiently strong natal kicks provided at least one of the black holes is spinning. Nutation is a consequence of spin-spin coupling and depends on the three spin-up mechanisms. Tidal synchronization can leave a distinct correlation between the aligned effective spin and the nutation frequency, but does not produce large nutations. When a black hole accretes $\gtrsim 20\%$ of its companion's envelope, the precession frequency and amplitude are large. A much smaller amount of accretion, e.g., $\approx 2\%$, is needed to provide a large precession frequency and amplitude when the accretor is a Wolf-Rayet (WR) star. The inheritance of high natal WR spins ($\gtrsim 5\%$ of their maximum breakup value) via minimal core-envelope coupling is the most promising mechanism for producing nutating BBHs, implying that a measurement of nutation from gravitational-wave observations may suggest isolated-binary origin with minimal core-envelope coupling.

astro-ph.HE↗

arXiv2022

On the LISA science performance in observations of short-lived signals from massive black hole binary coalescences

The observation of massive black hole binary systems is one of the main science objectives of the Laser Interferometer Space Antenna (LISA). The instrument's design requirements have recently been revised: they set a requirement at $0.1\,\mathrm{mHz}$, with no additional explicit requirements at lower frequencies. This has implications for observations of the short-lived signals produced by the coalescence of massive and high-redshift binaries. Here we consider the most pessimistic scenario: the (unlikely) case in which LISA has no sensitivity below $0.1\,\mathrm{mHz}$. We show that the presence of higher multipoles (beyond the dominant $\ell = |m| = 2$ mode) in the gravitational radiation from these systems, which will be detectable with a total signal-to-noise ratio $\sim 10^3$, allows LISA to retain the capability to accurately measure the physical parameters, the redshift, and to constrain the sky location. To illustrate this point, we consider a few select binaries in a total (redshifted) mass range of $4 \times10^6 - 4 \times 10^7\,M_\odot$ whose ($\ell = |m| = 2$) gravitational-wave signals last between $\approx 12$ hours and $\approx 20$ days in band. We model the emitted gravitational radiation using the highly accurate (spin-aligned) waveform approximant IMRPhenomXHM and carry out a fully coherent Bayesian analysis on the LISA noise-orthogonal time-delay-interferometry channels.

gr-qc↗

arXiv2022

Which black hole formed first? Mass-ratio reversal in massive binary stars from gravitational-wave data

Population inference of gravitational-wave catalogues is a useful tool to translate observations of black-hole mergers into constraints on compact-binary formation. Different formation channels predict identifiable signatures in the astrophysical distributions of source parameters, such as masses and spins. One example within the scenario of isolated binary evolution is mass-ratio reversal: even assuming efficient core-envelope coupling in massive stars and tidal spin-up of the stellar companion by the first-born black hole, a compact binary with a lighter, non-spinning first-born black hole and a heavier, spinning second-born black hole can still form through mass transfer from the initially more to less massive progenitor. Using current LIGO/Virgo observations, we measure the fraction of sources in the underlying population with this mass-spin combination and interpret it as a constraint on the occurrence of mass-ratio reversal in massive binary stars. We modify commonly used population models by including negligible-spin subpopulations and, most crucially, non-identical component spin distributions. We do not find evidence for subpopulations of black holes with negligible spins and measure the fraction of massive binary stars undergoing mass-ratio reversal to be consistent with zero and $<32\%$ ($99\%$ confidence). The dimensionless spin peaks around $0.2\unicode{x2013}0.3$ appear robust, however, and are yet to be explained by progenitor formation scenarios.

astro-ph.HE↗

arXiv2021

A taxonomy of black-hole binary spin precession and nutation

Binary black holes with misaligned spins will generically induce both precession and nutation of the orbital angular momentum $\bf{L}$ about the total angular momentum $\bf{J}$. These phenomena modulate the phase and amplitude of the gravitational waves emitted as the binary inspirals to merger. We introduce a "taxonomy" of binary black-hole spin precession that encompasses all the known phenomenology, then present five new phenomenological parameters that describe generic precession and constitute potential building blocks for future gravitational waveform models. These are the precession amplitude $\langleθ_L\rangle$, the precession frequency $\langle Ω_L\rangle$, the nutation amplitude $Δθ_L$, the nutation frequency $ω$, and the precession-frequency variation $ΔΩ_L$. We investigate the evolution of these five parameters during the inspiral and explore their statistical properties for sources with isotropic spins. In particular, we find that nutation of $\bf{L}$ is most prominent for binaries with high spins ($χ\gtrsim 0.5$) and moderate mass ratios ($q \sim 0.6$).

gr-qc↗