arXiv subjects

Irina Dvorkin

Publications and source records attributed to Irina Dvorkin.

At least 19 recordsLinked to original sources

arXiv2026

Binary neutron star populations across cosmic time: the impact of binary stellar evolution uncertainties

We investigate the impact of uncertainties in binary stellar evolution on the formation efficiency and cosmological merger rate of BNS systems. In particular, we aim to determine whether robust signatures of binary evolution can be identified across a broad range of metallicities. We perform a systematic exploration of 72 binary evolution models using the population synthesis code COSMIC. We vary four key parameters controlling the onset and efficiency of common-envelope evolution, the natal kick prescription, and the treatment of kicks during the common envelope phase. For each model, we compute the BNS formation efficiency and cosmological merger rate using several prescriptions for the cosmic metallicity-redshift relation. We identify characteristic features in the metallicity dependence of the BNS formation efficiency that arise from specific evolutionary processes. These include the onset of first-giant-branch skipping at low metallicity and a non-monotonic evolution between $Z=10^{-3}$ and $7.5\times 10^{-3}$. All models also predict a bimodal distribution of BNS progenitor masses associated with two distinct formation channels. The common envelope ejection efficiency and natal kick prescription remain the dominant sources of uncertainty, producing variations of several orders of magnitude in both the BNS formation efficiency and the cosmological merger rate. Finally, we show that different combinations of binary-evolution parameters can produce similar merger-rate histories, highlighting significant degeneracies among population-synthesis models. Current gravitational-wave observations can rule out only the least efficient formation scenarios. Breaking these degeneracies will require larger samples of BNS mergers expected from future third-generation gravitational-wave observatories, and improved observational constraints on the evolution of metallicity across cosmic time.

astro-ph.HE↗

arXiv2026

Probing the redshift evolution and sub-populations of binary neutron stars with the Einstein Telescope

The formation channels of binary neutron stars (BNSs) currently remain uncertain, but important information can be gathered by observing their mergers with gravitational-wave detectors. The processes that lead to BNS coalescence are encoded in the time-delay distribution between stellar binary formation and BNS coalescence, and therefore in the BNS merger rate. Moreover, the detection of GW190425 by LIGO/Virgo/KAGRA (LVK) suggests a sub-population of massive BNSs, possibly formed through unstable 'case BB' mass transfer with short merger delays. We investigate whether next-generation detectors can constrain the time-delay distribution of BNSs and identify such sub-populations. Using the latest LVK constraints, we generated mock catalogues that contain a mixture of light and heavy sub-populations. We modelled the redshift distribution of each sub-population as the convolution of the cosmic star formation rate with a time-delay distribution. We first considered a scenario where the time-delay distribution is common to all BNSs. In the second scenario, heavy BNSs have fixed short delays, while light BNSs follow power-law delays. Hierarchical Bayesian analyses were then performed on catalogues of 100-5000 events. With thousands of events, we should be able to accurately characterise the time-delay distribution for moderate time-delay indices. We find that with hundreds of detections, we will be able to establish that the total mass distribution is bimodal. A few thousand events are sufficient to disentangle the redshift distributions of the two sub-populations for moderate time-delay indices. For steeper indices, the differences are more subtle and require larger catalogues, which was beyond what we could explore given our computational resources.

astro-ph.HE↗

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↗

arXiv2025

Postmerger: a new and dominant contribution to the gravitational-wave background from binary neutron stars

The stochastic gravitational-wave background (SGWB) generated by the inspiral and merger of binary neutron stars is traditionally modelled assuming that the inspiral is promptly followed by the collapse of the merger remnant to a rotating black hole. While this is reasonable for the most massive binaries, it is not what is expected in general, as the remnant may survive for up to hundreds of milliseconds and radiate an amount of energy that is significantly larger than that lost during the whole inspiral. To account for this additional contribution to the SGWB, we consider a waveform model that includes both the inspiral and the postmerger emission. We show for the first time that for a large set of parameterized equations of state (EOSs) compatible with observational constraints, there is considerable spectral power in the $1-2\,{\rm kHz}$ range, distinct from that associated with the inspiral and leading to a dimensionless GW energy density $Ω_{\rm GW} \simeq 10^{-10}-10^{-9}$. We discuss the enhanced detectability of the SGWB by third-generation detectors such as the Einstein Telescope and Cosmic Explorer, and show how it depends on the signal-to-noise ratio of foreground binaries and on the remnant lifetime. Interestingly, even a non-detection of the high-frequency part of the SGWB could provide valuable constraints on the remnant lifetime, offering novel insights into the postmerger dynamics and the EOS of nuclear matter.

astro-ph.HE↗

arXiv2024

Evolutionary tracks of binary neutron star progenitors across cosmic times

Recent discoveries of gravitational wave sources have advanced our knowledge about the formation of compact object binaries. At present, many questions about the stellar origins of binary neutron stars remain open. We explore the evolution of binary neutron star progenitors with the population synthesis code COSMIC. We identify three dominant evolutionary tracks to form neutron star binaries that merge within the age of the Universe: a scenario that includes a common envelope phase between the first neutron star and its companion, a scenario with almost equal-mass progenitors that evolve quasi-simultaneously and which features a double-core common envelope, and a scenario involving the accretion-induced collapse of an oxygen-neon white dwarf into a neutron star. We show that the distribution of time delays between stellar formation and binary neutron star merger at a given progenitor metallicity does not follow a power-law, but instead features a complex structure that reflects the progenitor properties and the relative contribution of each evolutionary track. We also explore the evolution of the merger rate density with redshift and show that the scenario involving the accretion-induced collapse could be dominant at high redshifts. These results can have important implications for the study of the chemical enrichment of galaxies in r-process elements produced in kilonovae; and of short gamma-ray bursts offsets in their host galaxies.

astro-ph.HE↗

arXiv2024

Gravitational waves from mergers of Population III binary black holes: roles played by two evolution channels

The gravitational wave (GW) signal from binary black hole (BBH) mergers is a promising probe of Population III (Pop III) stars. To fully unleash the power of the GW probe, one important step is to understand the relative importance and features of different BBH evolution channels. We model two channels, isolated binary stellar evolution (IBSE) and nuclear star cluster-dynamical hardening (NSC-DH), in one theoretical framework based on the semi-analytical code A-SLOTH, under various assumptions on Pop III initial mass function (IMF), initial binary statistics and high-$z$ nuclear star clusters (NSCs). The NSC-DH channel contributes $\sim 8-95\%$ of Pop III BBH mergers across cosmic history, with higher contributions achieved by initially wider binary stars, more top-heavy IMFs, and more abundant high-$z$ NSCs. The dimensionless stochastic GW background (SGWB) produced by Pop III BBH mergers has peak values $Ω^{\rm peak}_{\rm GW}\sim 10^{-11}-8\times 10^{-11}$ around observer-frame frequencies $ν\sim 10-100\ \rm Hz$. The Pop III contribution can be a non-negligible ($\sim 2-32\%$) component in the total SGWB at $ν\lesssim 10\ \rm Hz$. The estimated detection rates of Pop III BBH mergers by the Einstein Telescope are $\sim 6-230\ \rm yr^{-1}$ and $\sim 30-1230\ \rm yr^{-1}$ for the NSC-DH and IBSE channels, respectively. Pop III BBH mergers in NSCs are more massive than those from IBSE, so they dominate the Pop III SGWB below $20$ Hz in most cases. Besides, the detection rate of Pop III BBH mergers involving at least one intermediate-mass BH above $100\ \rm M_\odot$ by the Einstein Telescope is $\sim 0.5-200\ \rm yr^{-1}$ in NSCs but remains below $0.1\ \rm yr^{-1}$ for IBSE.

astro-ph.GA↗

arXiv2023

Astrophysical Uncertainties in the Gravitational-Wave Background from Stellar-Mass Compact Binary Mergers

We investigate the Stochastic Gravitational Wave Background (SGWB) produced by merging binary black holes (BBHs) and binary neutron stars (BNSs) in the frequency ranges of LIGO/Virgo/Kagra and LISA. We develop three analytical models, that are calibrated to the measured local merger rates, and complement them with three population synthesis models based on the COSMIC code. We discuss the uncertainties, focusing on the impact of the BBH mass distribution, the effect of the metallicity of the progenitor stars and the time delay distribution between star formation and compact binary merger. We also explore the effect of uncertainties in binary stellar evolution on the background. For BBHs, our analytical models predict $Ω_{GW}$ in the range $[4.10^{-10}-1.10^{-9}]$ (25 Hz) and $[1.10^{-12}-4.10^{-12}]$ (3 mHz), and between $[2.10^{-10}-2.10^{-9}]$ (25 Hz) and $[7.10^{-13}- 7.10^{-12}]$ (3 mHz) for our population synthesis models. This background is unlikely to be detected during the LIGO/Virgo/Kagra O4 run, but could be detectable with LISA. We predict about 10 BBH and no BNS mergers that could be individually detectable by LISA for a period of observation of 4 years. Our study provides new insights into the population of compact binaries and the main sources of uncertainty in the astrophysical SGWB.

astro-ph.HE↗

arXiv2023

Astrophysics with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultracompact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

gr-qc↗

arXiv2023

pygwb: Python-based library for gravitational-wave background searches

The collection of gravitational waves (GWs) that are either too weak or too numerous to be individually resolved is commonly referred to as the gravitational-wave background (GWB). A confident detection and model-driven characterization of such a signal will provide invaluable information about the evolution of the Universe and the population of GW sources within it. We present a new, user-friendly Python--based package for gravitational-wave data analysis to search for an isotropic GWB in ground--based interferometer data. We employ cross-correlation spectra of GW detector pairs to construct an optimal estimator of the Gaussian and isotropic GWB, and Bayesian parameter estimation to constrain GWB models. The modularity and clarity of the code allow for both a shallow learning curve and flexibility in adjusting the analysis to one's own needs. We describe the individual modules which make up {\tt pygwb}, following the traditional steps of stochastic analyses carried out within the LIGO, Virgo, and KAGRA Collaboration. We then describe the built-in pipeline which combines the different modules and validate it with both mock data and real GW data from the O3 Advanced LIGO and Virgo observing run. We successfully recover all mock data injections and reproduce published results.

gr-qc↗

arXiv2022

The Effect of Mission Duration on LISA Science Objectives

The science objectives of the LISA mission have been defined under the implicit assumption of a 4 yr continuous data stream. Based on the performance of LISA Pathfinder, it is now expected that LISA will have a duty cycle of $\approx 0.75$, which would reduce the effective span of usable data to 3 yr. This paper reports the results of a study by the LISA Science Group, which was charged with assessing the additional science return of increasing the mission lifetime. We explore various observational scenarios to assess the impact of mission duration on the main science objectives of the mission. We find that the science investigations most affected by mission duration concern the search for seed black holes at cosmic dawn, as well as the study of stellar-origin black holes and of their formation channels via multi-band and multi-messenger observations. We conclude that an extension to 6 yr of mission operations is recommended.

astro-ph.IM↗

arXiv2021

The impact of turbulent mixing on the galactic r-process enrichment by binary neutron star mergers

We study the enrichment of the interstellar medium with rapid neutron capture (r-process) elements produced in binary neutron star (BNS) mergers. We use a semi-analytic model to describe galactic evolution, with merger rates and time delay distributions of BNS mergers consistent with the latest population synthesis models. In order to study the dispersion of the relative abundances of r-process elements and iron, we applied a turbulent mixing scheme, where the freshly synthesized elements are gradually dispersed in the interstellar medium. We show that within our model the abundances observed in Milky-Way stars, in particular the scatter at low metallicities, can be entirely explained by BNS mergers. Our results suggest that binary neutron star mergers could be the dominant source of r-process elements in the Galaxy.

astro-ph.HE↗

arXiv2020

Massive black hole merger rates: the effect of kpc separation wandering and supernova feedback

We revisit the predictions for the merger rate of massive black hole binaries detectable by the Laser Interferometer Space Antenna (LISA) and their background signal for pulsar-timing arrays. We focus on the effect of the delays between the merger of galaxies and the final coalescence of black hole binaries, and on supernova feedback on the black hole growth. By utilizing a semi-analytic galaxy formation model, not only do we account for the driving the evolution of binaries at separations $\lesssim 1$ pc (gas-driven migration, stellar hardening and triple/quadruple massive black hole systems), but we also improve on previous studies by accounting for the time spent by black hole pairs from kpc down to pc separation. We also include the effect of supernova feedback, which may eject gas from the nuclear region of low-mass galaxies, thus hampering the growth of black holes via accretion and suppressing their orbital migration in circumbinary disks. Despite including these novel physical effects, we predict that the LISA detection rate should still be $\gtrsim 2 \mbox{yr}^{-1}$, irrespective of the model for the black hole seeds at high redshifts. Scenarios where black holes form from $\sim100 M_\odot$ seeds are more significantly impacted by supernova feedback. We also find that for detectable events, the merging black holes typically have mass ratios between $\sim 0.1$ and $1$. Predictions for the stochastic background in the band of pulsar-timing array experiments are instead rather robust, and show only a mild dependence on the model.

astro-ph.GA↗

arXiv2020

Strong and weak lensing of Gravitational Waves: a semi-analytical approach

In this paper we study gravitational lensing of gravitational wave events. The main point of the present work is to introduce a semi-analytic approach so that each ingredient can be varied and tested individually. Our analytic model for the source population is motivated by a numerical study and we compare semi-analytical and numerical results. We determine the expected magnification for events seen at a given observed luminosity distance. We find that while the probability of significant magnification of the observed LIGO-Virgo events is very small, the probability distribution of the magnification has a significant tail to high $μ$ such that e.g. the variance of the magnification is very large and even diverges in the geometric optics approximation. For the 10 binary black hole mergers observed by LIGO-Virgo in the O1+O2 observation campaigns, the probability that one of them has been magnified with magnification of 5 or bigger is $\mathcal{P}_{\text{obs}}(>5)\sim 0.01$ while the probability of magnification by 50 or bigger is $\mathcal{P}_{\text{obs}}(>50)\sim 0.005$.

astro-ph.CO↗

arXiv2019

Stochastic gravitational wave background anisotropies in the mHz band: astrophysical dependencies

We show that the anisotropies of the astrophysical stochastic gravitational wave background in the mHz band have a strong dependence on the modelling of galactic and sub-galactic physics. We explore a wide range of self-consistent astrophysical models for stellar evolution and for the distribution of orbital parameters, all calibrated such that they predict the same number of resolved mergers to fit the number of detections during LIGO/Virgo O1+O2 observations runs. We show that different physical choices for the process of black hole collapse and cut-off in the black hole mass distribution give fractional differences in the angular power spectrum of anisotropies up to 50\% on all angular scales. We also point out that the astrophysical information which can be extracted from anisotropies is complementary to the isotropic background and individual mergers. These results underline the interest in the anisotropies of the stochastic gravitational wave background as a new and potentially rich field of research, at the cross-road between astrophysics and cosmology.

astro-ph.CO↗

arXiv2019

High angular resolution gravitational wave astronomy

Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy to obtain for observations in the electromagnetic spectrum, the positional accuracy of current and near future gravitational wave detectors is limited to between tens and hundreds of square degrees, which makes it extremely challenging to identify the host galaxies of gravitational wave events or to confidently detect any electromagnetic counterparts. Gravitational wave observations provide information on source properties and distances that is complementary to the information in any associated electromagnetic emission and that is very hard to obtain in any other way. Observing systems with multiple messengers thus has scientific potential much greater than the sum of its parts. A gravitational wave detector with higher angular resolution would significantly increase the prospects for finding the hosts of gravitational wave sources and triggering a multi-messenger follow-up campaign. An observatory with arcminute precision or better could be realised within the Voyage 2050 programme by creating a large baseline interferometer array in space and would have transformative scientific potential. Precise positional information of standard sirens would enable precision measurements of cosmological parameters and offer new insights on structure formation; a high angular resolution gravitational wave observatory would allow the detection of a stochastic background and resolution of the anisotropies within it; it would also allow the study of accretion processes around black holes; and it would have tremendous potential for tests of modified gravity and the discovery of physics beyond the Standard Model.

astro-ph.HE↗

arXiv2019

Properties of the stochastic astrophysical gravitational wave background: astrophysical sources dependencies

This article explores the properties (amplitude and shape) of the angular power spectrum of the anisotropies of the astrophysical gravitational wave background (AGWB) focusing on the signatures of the astrophysical models describing sub-galactic physics. It demonstrates that while some parameters have negligible impact others, and in particular the stellar evolution models, the metallicity and the merger time delay distribution can result in relative differences of order 40% in the angular power spectrum of anisotropies in both the LIGO/Virgo and LISA frequency bands. It is also shown that the monopole and the anisotropic components of the AGWB are complementary and sensitive to different astrophysical parameters. It follows that AGWB anisotropies are a new observable with the potential to provide new astrophysical information that can not be accessed otherwise.

astro-ph.CO↗

arXiv2018

Comment on the article "Anisotropies in the astrophysical gravitational-wave background: The impact of black hole distributions" by A.C. Jenkins et al. [arXiv:1810.13435]

We investigate the discrepancy pointed out by Jenkins et al. in Ref. [1] between the predictions of anisotropies of the astrophysical gravitational wave (GW) background, derived using different methods in Cusin et al. [2] and in Jenkins et al. [3]. We show that this discrepancy is not due to our treatment of galaxy clustering, contrary to the claim made in Ref. [1] and we show that our modeling of clustering gives results in very good agreement with observations. Furthermore we show that the power law spectrum used in Refs. [1] and [3] to describe galaxy clustering is incorrect on large scales and leads to a different scaling of the multipoles $C_\ell$. Moreover, we also explain that the analytic derivation of the gravitational wave background correlation function in Refs. [1] and [3] is mathematically ill-defined and predicts an amplitude of the angular power spectrum which depends on the (arbitrary) choice of a non-physical cut-off.

astro-ph.CO↗

arXiv2018

The stochastic gravitational-wave background in the absence of horizons

Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein's theory: the existence of black holes. A plethora of ultracompact, horizonless objects have been proposed to arise in models inspired by quantum gravity. These objects may solve Hawking's information-loss paradox and the singularity problem associated with black holes, while mimicking almost all of their classical properties. They are, however, generically unstable on relatively short timescales. Here, we show that this "ergoregion instability" leads to a strong stochastic background of gravitational waves, at a level detectable by current and future gravitational-wave detectors. The absence of such background in the first observation run of Advanced LIGO already imposes the most stringent limits to date on black-hole alternatives, showing that certain models of "quantum-dressed" stellar black holes can be at most a small percentage of the total population. The future LISA mission will allow for similar constraints on supermassive black-hole mimickers.

gr-qc↗