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<!DOCTYPE html>
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<title>COMPAS | Science</title>
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<h1><a href="index.html" id="logo">COMPAS <em>|
Science</em></a>
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<a href="index.html">About</a>
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<li class="current">
<a href="science.html">Science</a>
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<a href=
"science.html#intro">Introduction</a>
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<!-- Left Column: Opening Paragraph & Papers -->
<div class="8u 12u(narrower)">
<div id="content">
<!-- Opening Paragraph -->
<article>
<header>
<h2 id="intro">How do binary
black holes form?</h2>
<p>Unravelling binary
physics</p>
</header>
<p>We are making progress in
understanding how two black holes
can come together and merge.</p>
<p>On the 14th September 2015,
Advanced LIGO (Laser Interferometer
Gravitational-wave Observatory)
detected gravitational waves from
the collision of a pair of black
holes, dubbed GW150914. Since then,
Advanced LIGO has been joined by
Advanced Virgo. Together, Advanced
LIGO and Virgo observed GW170817,
gravitational waves from the
inspiral and merger of a pair of
neutron stars. This event was
subsequently observed across the
electromagnetic spectrum, including
as a gamma ray burst and kilonova.
At the end of their first two
observing runs, Advanced LIGO and
Virgo had totalled up 10 binary
black hole mergers and one binary
neutron star merger. Their third
observing run finished in March
2020.</p>
<p>These observations confirmed a
major prediction of Albert
Einstein's 1915 general theory of
relativity and opened an
unprecedented new window onto the
cosmos. However, we still do not
know how such pairs of merging
black holes and neutron stars
form.</p>
<p>In order for black holes to
merge within the age of the
Universe by emitting gravitational
waves, they must start out close
together by astronomical standards,
no more than about a fifth of the
distance between the Earth and the
Sun for the heaviest LIGO sources.
However, massive stars, which are
the progenitors of the black holes
that LIGO observes, expand to be
much larger than this in the course
of their evolution. The key
challenge, then, is how to fit such
large stars within a very small
orbit. <a href=
"http://adsabs.harvard.edu/abs/2018arXiv180605820M">
Several possible scenarios</a> have
been proposed to address this.</p>
<p>We use COMPAS to investigate
massive binary evolution and
constrain it with a range of
observational data sets. Our code
is publicly available at <a href=
"https://github.com/TeamCOMPAS/COMPAS">
https://github.com/TeamCOMPAS/COMPAS</a>,
Further information can be found in
<a href=
"http://arXiv.org/abs/2109.10352">the
COMPAS methods paper</a> or in more
technical <a href=
"https://compas.science/docs">documentation</a>.
The <a href=
"https://zenodo.org/record/6346444#.YjGanxBByfU">
latest COMPAS data release</a> is
available through our <a href=
"https://zenodo.org/communities/compas/">
zenodo community.</a></p>
</article>
<!-- Papers Header -->
<header id="papers" class="major">
<h2>Selected Papers</h2>
<p>Summaries and data releases of
papers which directly use
COMPAS</p>
</header>
<!-- Complete list of papers -->
<article>
<p><strong>Note:</strong> The data
used in some of the COMPAS papers
has been made available to the
public.<br>
For access, please see <a href=
"https://zenodo.org/communities/compas/?page=1&size=20">
our Zenodo page</a>, or check the
appropriate paper below.</p>
For a complete list of COMPAS
papers, see <a href=
"https://ui.adsabs.harvard.edu/public-libraries/gzRk1qpbRUy4cP2GydR36Q">
our ADS library</a>
</article>
<br>
<br>
<!-- -->
<!-- INSERT PAPERS BELOW -->
<!-- Boesky et al. 2024 -->
<article>
<header>
<h2 id="240501630" style="margin-bottom:0.5em"> Investigating the Cosmological Rate of Compact Object Mergers from Isolated Massive Binary Stars </h2>
<h1><strong>Boesky et al. 2024</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Adam Boesky; Floor S. Broekgaarden; Edo Berger
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2405.01630.pdf">2405.01630</a></p>
<!-- Description -->
<p>
ravitational wave detectors are observing compact object mergers from increasingly far distances, revealing the redshift evolution of the binary black hole (BBH) -- and soon the black hole-neutron star (BHNS) and binary neutron star (BNS) -- merger rate. To help interpret these observations, we investigate the expected redshift evolution of the compact object merger rate from the isolated binary evolution channel. We present a publicly available catalog of compact object mergers and their accompanying cosmological merger rates from population synthesis simulations conducted with the COMPAS software. To explore the impact of uncertainties in stellar and binary evolution, our simulations use two-parameter grids of binary evolution models that vary the common-envelope efficiency with mass transfer accretion efficiency, and supernova remnant mass prescription with supernova natal kick velocity, respectively. We quantify the redshift evolution of our simulated merger rates using the local ($z\sim 0$) rate, the redshift at which the merger rate peaks, and the normalized differential rates (as a proxy for slope). We find that although the local rates span a range of $\sim 10^3$ across our model variations, their redshift-evolutions are remarkably similar for BBHs, BHNSs, and BNSs, with differentials typically within a factor $3$ and peaks of $z\approx 1.2-2.4$ across models. Furthermore, several trends in our simulated rates are correlated with the model parameters we explore. We conclude that future observations of the redshift evolution of the compact object merger rate can help constrain binary models for stellar evolution and gravitational-wave formation channels.
</p>
</div>
</article>
<!-- Song et al. 2024 -->
<article>
<header>
<h2 id="240611428" style="margin-bottom:0.5em"> Binary population synthesis of the Galactic canonical pulsar population </h2>
<h1><strong>Song et al. 2024</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Yuzhe Song; Simon Stevenson; Debatri Chattopadhyay
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2406.11428.pdf">2406.11428</a></p>
<!-- Description -->
<p>
ulsars are rapidly rotating neutron stars that emit radiation across the electromagnetic spectrum, from radio to gamma-rays. We use the rapid binary population synthesis suite COMPAS to model the Galactic population of canonical pulsars. We account for both radio and gamma-ray selection effects, as well as the motion of pulsars in the Galactic potential due to natal kicks. We compare our models to the catalogs of pulsars detected in the radio, and those detected in gamma-rays by Fermi, and find broad agreement with both populations. We reproduce the observed ratio of radio-loud to radio-quiet gamma-ray pulsars. We further examine the possibility of low spin-down luminosity (Edot) pulsars emitting weak, unpulsed gamma-ray emission and attempt to match this with recent stacking results. We demonstrate that the apparent correlation between the latitude of a pulsar and its Edot arises due to natal kicks imparted to pulsars at birth, assuming that all pulsars are born in the Galactic disk.
</p>
</div>
</article>
<!-- Rauf et al. 2024 -->
<article>
<header>
<h2 id="240611885" style="margin-bottom:0.5em"> A Trifecta of Modelling Tools: Navigating COMPAS, Shark and Bayesian Inference for Binary Black Hole Model Selection </h2>
<h1><strong>Rauf et al. 2024</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Liana Rauf; Cullan Howlett; Simon Stevenson; Jeff Riley
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2406.11885.pdf">2406.11885</a></p>
<!-- Description -->
<p>
ravitational waves (GWs) have revealed surprising properties of binary black hole (BBH) populations, but there is still mystery surrounding how these compact objects evolve. We apply Bayesian inference and an efficient method to calculate the BBH merger rates in the Shark host galaxies, to determine the combination of COMPAS parameters that outputs a population most like the GW sources from the LVK transient catalogue. For our COMPAS models, we calculate the likelihood with and without the dependence on the predicted number of BBH merger events. We find strong correlations between hyper-parameters governing the specific angular momentum (AM) of mass lost during mass transfer, the mass-loss rates of Wolf--Rayet stars via winds and the chemically homogeneous evolution (CHE) formation channel. We conclude that analysing the marginalised and unmarginalised likelihood is a good indicator of whether the population parameters distribution and number of observed events reflect the LVK data. In doing so, we see that the majority of the models preferred in terms of the population-level parameters of the BBHs greatly overpredict the number of events we should have observed to date. Looking at the smaller number of models which perform well with both likelihoods, we find that those with no CHE, AM loss occurring closer to the donor during the first mass-transfer event, and/or higher rates of mass-loss from Wolf--Rayet winds are generally preferred by current data. We find these conclusions to be robust to our choice of selection criteria.
</p>
</div>
</article>
<!-- Nathaniel et al. 2024 -->
<article>
<header>
<h2 id="240711680" style="margin-bottom:0.5em"> Population synthesis of Thorne-Żytkow objects: Rejuvenated donors and unexplored progenitors in the common envelope formation channel </h2>
<h1><strong>Nathaniel et al. 2024</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
K. Nathaniel; A. Vigna-Gómez; A. Grichener; R. Farmer; M. Renzo; R. W. Everson
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2407.11680.pdf">2407.11680</a></p>
<!-- Description -->
<p>
ontext. Common envelope evolution of a massive star and a neutron star companion has two possible outcomes: formation of a short-period binary (a potential gravitational wave source progenitor) or a merger of the massive star with the neutron star. If the binary merges, a structure with a neutron star core surrounded by a large diffuse envelope, a so-called Thorne-\.Zytkow object (T\.ZO), may form. The predicted appearance of this hypothetical class of star is very similar to red supergiants, making observational identification difficult. Aims. Our objective is to understand the properties of systems that are potential T\.ZO progenitors, e.g., binary systems that enter a common envelope phase with a neutron star companion. We also aim to distinguish those that have been through a previous stable mass transfer phase, which can rejuvenate the accretor. We estimate the number of T\.ZOs in the Milky Way and assess the impact of uncertainties in their formation. Methods. We use the rapid population synthesis code COMPAS at Solar metallicity and with common envelope efficiency parameter set to unity to determine the population demographics of T\.ZOs. We use one-dimensional evolutionary T\.ZO models from the literature to determine a fit for T\.ZO lifetime in order to estimate the current number of T\.ZOs in the Galaxy as well as to assess core disruption during the merger. Results. We explore the progenitors in the Hertzsprung-Russell diagram, calculate formation rates, and investigate kinematics of the progenitor stars. We find that the vast majority ($\approx 92\%$) of T\.ZO progenitors in our population have experienced mass transfer and become rejuvenated before their formation event. Using a constant star formation rate we estimate $\approx 2\times 10 ^{-4}$ T\.ZOs per $M_\odot$ in our Galaxy, corresponding to $\approx 5\pm 1$ T\.ZOs in the Milky Way at present.
</p>
</div>
</article>
<!-- Rauf et al. v2) -->
<article>
<header>
<h2 id="230208172" style="margin-bottom:0.5em"> Exploring binary black hole mergers and host galaxies with Shark and COMPAS </h2>
<h1><strong>Rauf et al. v2)</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Liana Rauf; Cullan Howlett; Tamara M. Davis; Claudia D. P. Lagos
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2302.08172.pdf">2302.08172</a></p>
<!-- Description -->
<p>
e explore the connection between the gravitational wave (GW) merger rates of stellar-mass binary black holes (BBH) and galaxy properties. We do this by generating populations of stars using the binary population synthesis code COMPAS and evolving them in galaxies from the semi-analytic galaxy formation model Shark, to determine the number of mergers occurring in each simulation time-step. We find that metal-rich and massive galaxies with star formation rate (SFR) greater than $1M_{\odot}/ \rm yr$ are 10 times more likely to have GW events compared to younger, less massive and metal poor galaxies. Our simulation with the default input parameters predicts a higher local merger rate density compared to the third GW transient catalogue (GWTC-3) prediction from LIGO, VIRGO and KAGRA, due to short coalescence times, low metallicities and a high SFR at low redshift in the simulation, which produces more BBHs that merge within the age of the Universe compared to observations. We identify alternate remnant mass models that more accurately reproduce the volumetric rate and provide updated fits to the merger rate as a function of redshift. We then investigate the relative fraction of GW events in our simulation that are in observable host galaxies from upcoming galaxy surveys, determining which of those are ideal for tracing host galaxies with high merger rates. The implications of this work can be utilised for constraining stellar evolution models, better informing follow-up programs, and placing informative priors on host galaxies when measuring cosmological parameters such as the Hubble constant.
</p>
</div>
</article>
<!-- Boesky et al. 2024 -->
<article>
<header>
<h2 id="240501623" style="margin-bottom:0.5em"> The Binary Black Hole Merger Rate Deviates From the Cosmic Star Formation Rate: A Tug of War Between Metallicity and Delay Times </h2>
<h1><strong>Boesky et al. 2024</strong><h1>
</header>
<button class="collapsible">Details</button>
<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Adam Boesky; Floor S. Broekgaarden; Edo Berger
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2405.01623.pdf">2405.01623</a></p>
<!-- Description -->
<p>
ravitational-wave detectors are now making it possible to investigate how the merger rate of binary black holes (BBHs) evolves with redshift. In this study, we examine whether the BBH merger rate of isolated binaries deviates from a scaled star formation rate density (SFRD) -- a frequently used model in state-of-the-art research. To address this question, we conduct population synthesis simulations using COMPAS with a grid of stellar evolution models, calculate their cosmological merger rates, and compare them to a scaled SFRD. We find that our simulated rates deviate by factors up to $3.5\times$ at $z\sim0$ and $5\times$ at $z\sim 9$ due to two main phenomena: (i) The formation efficiency of BBHs is an order of magnitude higher at low metallicities than at solar metallicity; and (ii) BBHs experience a wide range of delays (from a few Myr to many Gyr) between formation and merger. Deviations are similar when comparing to a $\textit{delayed}$ SFRD, and even larger (up to $\sim 10\times$) when comparing to SFRD-based models scaled to the local merger rate. Interestingly, our simulations find that the BBH delay time distribution is redshift-dependent, increasing the complexity of the redshift distribution of mergers. We find similar results for simulated merger rates of BHNSs and BNSs. We conclude that the rate of BBH, BHNS, and BNS mergers from the isolated channel can significantly deviate from a scaled SFRD, and that future measurements of the merger rate will provide insights into the formation pathways of gravitational-wave sources.
</p>
</div>
</article>
<!-- Willcox et al. 2023 -->
<article>
<header>
<h2 id="230806666" style="margin-bottom:0.5em"> The Impact of Angular Momentum Loss on the Outcomes of Binary Mass Transfer </h2>
<h1><strong>Willcox et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Reinhold Willcox; Morgan MacLeod; Ilya Mandel; Ryosuke Hirai
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2308.06666.pdf">2308.06666</a></p>
<!-- Description -->
<p>
e use the rapid binary population synthesis code COMPAS to investigate commonly used prescriptions for the determination of mass transfer stability in close binaries and the orbital separations after stable mass transfer. The degree of orbital tightening during non-conservative mass transfer episodes is governed by the poorly-constrained angular momentum carried away by the ejected material. Increased orbital tightening drives systems towards unstable mass transfer leading to a common envelope. We find that the fraction of interacting binaries that will undergo only stable mass transfer throughout their lives fluctuates between a few and $\sim 20\%$ due to uncertainty in the angular momentum loss alone. If mass transfer is significantly non-conservative, stability prescriptions that rely on the assumption of conservative mass transfer under-predict the number of systems which experience unstable mass transfer and stellar mergers. This may substantially impact predictions about the rates of various transients, including luminous red novae, stripped-envelope supernovae, X-ray binaries, and the progenitors of coalescing compact binaries.
</p>
</div>
</article>
<!-- Mosbech et al. v3) -->
<article>
<header>
<h2 id="220714126" style="margin-bottom:0.5em"> Gravitational-wave event rates as a new probe for dark matter microphysics </h2>
<h1><strong>Mosbech et al. v3)</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Markus R. Mosbech; Alexander C. Jenkins; Sownak Bose; Celine Boehm; Mairi Sakellariadou; Yvonne Y. Y. Wong
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2207.14126.pdf">2207.14126</a></p>
<!-- Description -->
<p>
e show that gravitational waves have the potential to unravel the microphysical properties of dark matter due to the dependence of the binary black hole merger rate on cosmic structure formation, which is itself highly dependent on the dark matter scenario. In particular, we demonstrate that suppression of small-scale structure -- such as that caused by interacting, warm, or fuzzy dark matter -- leads to a significant reduction in the rate of binary black hole mergers at redshifts $z\gtrsim5$. This shows that future gravitational-wave observations will provide a new probe of physics beyond the $\Lambda$CDM model.
</p>
</div>
</article>
<!-- Grichener et al. v2) -->
<article>
<header>
<h2 id="230206663" style="margin-bottom:0.5em"> Mergers of neutron stars and black holes with cores of giant stars: a population synthesis study </h2>
<h1><strong>Grichener et al. v2)</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Aldana Grichener
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2302.06663.pdf">2302.06663</a></p>
<!-- Description -->
<p>
e perform population synthesis of massive binaries to study the mergers of neutron stars (NSs) and black holes (BHs) with the cores of their giant secondaries during common envelope evolution (CEE). We use different values of the efficiency parameter $\alpha_{\rm CE}$ in the framework of the energy formalism for traditional CEE ($\alpha_{\rm CE} \leq 1$) and including additional energy sources to unbind the envelope ($\alpha_{\rm CE} > 1$). We constrain the possible values of $\alpha_{\rm CE}$ by comparing the results of our simulations with local rate densities of binary compact object mergers as inferred from gravitational-wave observations. We find two main evolutionary pathways of binary systems that result in NS-core mergers, while only one of them can also lead to the merger of a BH with the core of the giant star. We explore the zero age main sequence (ZAMS) statistical properties of systems that result in NS/BH-core mergers and find that the two evolutionary channels correspond to a bimodal distribution of orbital separations. We estimate the percentage of the mergers' event rates relative to core collapse supernovae (CCSNe). We include the effect of mass accreted by the NS/BH during CEE in a separate set of simulations and find it does not affect the mergers' event rates.
</p>
</div>
</article>
<!-- Agudo et al. v3) -->
<article>
<header>
<h2 id="220809000" style="margin-bottom:0.5em"> Panning for gold, but finding helium: discovery of the ultra-stripped supernova SN2019wxt from gravitational-wave follow-up observations </h2>
<h1><strong>Agudo et al. v3)</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
I. Agudo; L. Amati; T. An; F. E. Bauer; S. Benetti; M. G. Bernardini; R. Beswick; K. Bhirombhakdi; T. de Boer; M. Branchesi; S. J. Brennan; M. D. Caballero-García; E. Cappellaro; N. Castro Rodríguez; A. J. Castro-Tirado; K. C. Chambers; E. Chassande-Mottin; S. Chaty; T.-W. Chen; A. Coleiro; S. Covino; F. D'Ammando; P. D'Avanzo; V. D'Elia; A. Fiore; A. Flörs; M. Fraser; S. Frey; C. Frohmaier; L. Galbany; C. Gall; H. Gao; J. García-Rojas; G. Ghirlanda; S. Giarratana; J. H. Gillanders; M. Giroletti; B. P. Gompertz; M. Gromadzki; K. E. Heintz; Y.-D. Hu; M. E. Huber; A. Inkenhaag; L. Izzo; Z. P. Jin; P. G. Jonker; D. A. Kann; E. C. Kool; R. Kotak; G. Leloudas; A. J. Levan; C.-C. Lin; J. D. Lyman; E. A. Magnier; K. Maguire; I. Mandel; B. Marcote; D. Mata Sánchez; S. Mattila; A. Melandri; M. J. Michałowski; J. Moldon; M. Nicholl; A. Nicuesa Guelbenzu; S. R. Oates; F. Onori; M. Orienti; R. Paladino; Z. Paragi; M. Perez-Torres; E. Pian; G. Pignata; S. Piranomonte; J. Quirola-Vásquez; F. Ragosta; A. Rau; S. Ronchini; A. Rossi; R. Sánchez-Ramírez; O. S. Salafia; S. Schulze; S. J. Smartt; K. W. Smith; J. Sollerman; S. Srivastav; R. L. C. Starling; D. Steeghs; H. F. Stevance; V. Testa; M. A. P. Torres; S. D. Vergani; D. Vescovi; R. Wainscost; D. Watson; K. Wiersema; Ł. Wyrzykowski; J. Yang; S. Yang; D. R. Young
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2208.09000.pdf">2208.09000</a></p>
<!-- Description -->
<p>
e present the results from multi-wavelength observations of a transient discovered during the follow-up of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN2019wxt, a young transient in a galaxy whose sky position (in the 80\% GW contour) and distance ($\sim$150\,Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude ($M_i \sim -16.7$\,mag) and the $r-$band decline rate of $\sim 1$\,mag per 5\,days appeared suggestive of a compact binary merger. However, SN2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of $\sim 0.1\,M_\odot$, with $^{56}$Ni comprising $\sim 20\%$ of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitors that could give rise to the observed properties of SN2019wxt, and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling electromagnetic counterparts to GW events from transients such as SN2019wxt is challenging: in a bid to characterise the level of contamination, we estimated the rate of events with properties comparable to those of SN2019wxt and found that $\sim 1$ such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500\,Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
</p>
</div>
</article>
<!-- Méndez et al. 2022 -->
<article>
<header>
<h2 id="220703514" style="margin-bottom:0.5em"> Hypercritical accretion during common envelopes in triples leading to binary black holes in the pair-instability-supernova mass gap </h2>
<h1><strong>Méndez et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Enrique Moreno Méndez; Fabio De Colle; Diego López Cámara; Alejandro Vigna-Gómez
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2207.03514.pdf">2207.03514</a></p>
<!-- Description -->
<p>
ydrodynamic studies of stellar-mass compact objects (COs) in a common envelope (CE)have shown that the accretion rate onto the CO is a few orders of magnitude below the Bondi-Hoyle-Lyttleton (BHL) estimate. This is several orders of magnitude above the Eddington limit and above the limit for neutrino-cooled accretion (i.e., hypercritical accretion, or HCA). Considering that a binary system inside the CE of a third star accretes material at nearly the same rate as a single object of the same total mass, we propose stellar-evolution channels which form binary black hole (BBH) systems with its component masses within the pair-instability supernova (PISN) mass gap. Our model is based on HCA onto the BBH system engulfed into the CE of a massive tertiary star. Furthermore, we propose a mass transfer mode which allows to store mass lost by the binary onto a third star. Through the use of population synthesis simulations for the evolution of BBHs and standard binary-evolution principles for the interaction with a tertiary star, we are able to produce BBHs masses consistent with those estimated for GW190521. We also discuss the massive binary system Mk34 as a possible progenitor of BBHs in the PISN gap, as well as the spin distribution of the observed mergers in the gravitational-wave catalog.
</p>
</div>
</article>
<!-- Kobayashi et al. v2) -->
<article>
<header>
<h2 id="221104964" style="margin-bottom:0.5em"> Can neutron star mergers alone explain the r-process enrichment of the Milky Way? </h2>
<h1><strong>Kobayashi et al. v2)</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Chiaki Kobayashi; Ilya Mandel; Krzysztof Belczynski; Stephane Goriely; Thomas H. Janka; Oliver Just; Ashley J. Ruiter; Dany Van Beveren; Matthias U. Kruckow; Max M. Briel; Jan J. Eldridge; Elizabeth Stanway
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2211.04964.pdf">2211.04964</a></p>
<!-- Description -->
<p>
omparing Galactic chemical evolution models to the observed elemental abundances in the Milky Way, we show that neutron star mergers can be a leading r-process site only if at low metallicities such mergers have very short delay times and significant ejecta masses that are facilitated by the masses of the compact objects. Namely, black hole-neutron star mergers, depending on the black-hole spins, can play an important role in the early chemical enrichment of the Milky Way. We also show that none of the binary population synthesis models used in this paper, i.e., COMPAS, StarTrack, Brussels, ComBinE, and BPASS, can currently reproduce the elemental abundance observations. The predictions are problematic not only for neutron star mergers, but also for Type Ia supernovae, which may point to shortcomings in binary evolution models.
</p>
</div>
</article>
<!-- Romero-Shaw et al. 2023 -->
<article>
<header>
<h2 id="230305375" style="margin-bottom:0.5em"> Rapid population synthesis of black-hole high-mass X-ray binaries: implications for binary stellar evolution </h2>
<h1><strong>Romero-Shaw et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Isobel M. Romero-Shaw; Ryosuke Hirai; Arash Bahramian; Reinhold Willcox; Ilya Mandel
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2303.05375.pdf">2303.05375</a></p>
<!-- Description -->
<p>
We conduct a binary population synthesis study to investigate the formation of wind-fed high-mass X-ray binaries containing black holes (BH-HMXBs). We evolve multiple populations of high-mass binary stars and consider BH-HMXB formation rates, masses, spins and separations. We find that systems similar to Cygnus X-1 likely form after stable Case A mass transfer (MT) from the main sequence progenitors of black holes, provided such MT is characterised by low accretion efficiency, $\beta \lesssim 0.1$, with modest orbital angular momentum losses from the non-accreted material. Additionally, BH-HMXB formation relies on a new simple treatment for Case A MT that allows donors to retain larger core masses compared to traditional rapid population-synthesis procedures. At solar metallicity, our Preferred model yields $\mathcal{O}(1)$ observable BH-HMXBs in the Galaxy today, consistent with observations. In this simulation, $8\%$ of BH-HMXBs go on to merge as binary black holes or neutron star--black hole binaries within a Hubble time. Compact-object mergers that evolve via a BH-HMXB phase may contribute $\gtrsim20$~Gpc$^{-3}$~yr$^{-1}$ to the merger rate inferred from gravitational-wave observations. We also suggestthat MT efficiency is higher during stable Case B MT than during Case A MT.
</p>
</div>
</article>
<!-- Vigna-Gómez et al. -->
<article>
<header>
<h2 id="220308478" style="margin-bottom:0.5em"> A binary origin for the first isolated stellar-mass black hole detected with astrometric microlensing </h2>
<h1><strong>Vigna-Gómez et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Alejandro Vigna-Gómez; Enrico Ramirez-Ruiz
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2203.08478.pdf">2203.08478</a></p>
<!-- Description -->
<p>
The Milky Way is believed to host hundreds of millions of quiescentstellar-mass black holes (BHs). In the last decade, some of these objects havebeen potentially uncovered via gravitational microlensing events. All thesedetections resulted in a degeneracy between the velocity and the mass of thelens. This degeneracy has been lifted, for the first time, with the recentastrometric microlensing detection of OB110462. However, two independentstudies reported very different lens mass for this event. Sahu et al. (2022)inferred a lens mass of 7.1 $\pm$ 1.3 Msun, consistent with a BH, while Lam etal. (2022) inferred 1.6-4.2 Msun, consistent with either a neutron star or aBH. Here, we study the landscape of isolated BHs formed in the field. Inparticular, we focus on the mass and center-of-mass speed of foursub-populations: isolated BHs from single-star origin, disrupted BHs ofbinary-star origin, main-sequence stars with a compact object companion, anddouble compact object mergers. Our model predicts that most ($\gtrsim$ 70%)isolated BHs in the Milky Way are of binary origin. However, non-interactionslead to most massive BHs ($\gtrsim$ 15-20 Msun) being predominantly of singleorigin. Under the assumption that OB110462 is a free-floating compact object weconclude that it is more likely to be a BH originally belonging to a binarysystem. Our results suggest that low-mass BH microlensing events can be usefulto understand binary evolution of massive stars in the Milky Way, whilehigh-mass BH lenses can be useful to probe single stellar evolution.
</p>
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</article>
<!-- Riley et al. 2023 -->
<article>
<header>
<h2 id="230300508" style="margin-bottom:0.5em"> Surrogate Forward Models for Population Inference on Compact Binary Mergers </h2>
<h1><strong>Riley et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Jeff Riley; Ilya Mandel
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2303.00508.pdf">2303.00508</a></p>
<!-- Description -->
<p>
Rapidly growing catalogs of compact binary mergers from advanced gravitational-wave detectors allow us to explore the astrophysics of massive stellar binaries. Merger observations can constrain the uncertain parameters that describe the underlying processes in the evolution of stars and binary systems in population models. In this paper, we demonstrate that binary black hole populations - namely, detection rates, chirp masses, and redshifts - can be used to measure cosmological parameters describing the redshift-dependent star formation rate and metallicity distribution. We present a method that uses artificial neural networks to emulate binary population synthesis computer models, and construct a fast, flexible, parallelisable surrogate model that we use for inference.
</p>
</div>
</article>
<!-- Rauf et al. 2023 -->
<article>
<header>
<h2 id="230208172" style="margin-bottom:0.5em"> Exploring binary black hole mergers and host galaxies with Shark and COMPAS </h2>
<h1><strong>Rauf et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Liana Rauf; Cullan Howlett; Tamara M. Davis; Claudia D. P. Lagos
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2302.08172.pdf">2302.08172</a></p>
<!-- Description -->
<p>
In this work, we explore the connection between the gravitational wave (GW)merger rates of stellar-mass binary black holes (BBH) and galaxy properties. Wedo this by generating populations of stars using the binary synthesis codeCOMPAS and evolving them in galaxies from the semi-analytic galaxy formationmodel {\sc Shark}, to determine the number of mergers occurring in eachsimulation time-step. We find that large, metal-rich galaxies with high starformation rates are more likely to have gravitational wave (GW) events comparedto younger, more metal poor galaxies. Our simulation with the default inputparameters predicts a higher local merger rate density compared to the thirdgravitational wave transient catalogue (GWTC-3) prediction from LIGO, VIRGO andKAGRA. This is due to short coalescence times, low metallicities and an highformation rate of stars at low redshift in the galaxy simulation, whichproduces more BBHs that merge within the age of the Universe compared toobservations. We identify alternate remnant mass models that more accuratelyreproduce the observed volumetric rate and provide updated fits to the mergerrate distribution as a function of redshift. We then investigate the relativefraction of GW events in our simulation volume that are in observable hostgalaxies from different upcoming photometric and spectroscopic surveys,determining which of those are more ideal for tracing host galaxies with highmerger rates. The implications of this work can be utilised for numerousapplications, including for constraining stellar evolution models, betterinforming follow-up programs, and placing more informative priors on potentialhost galaxies when measuring cosmological parameters such as the Hubbleconstant.
</p>
</div>
</article>
<!-- Grichener et al. 2023 -->
<article>
<header>
<h2 id="230206663" style="margin-bottom:0.5em"> Mergers of neutron stars and black holes with cores of giant stars: a population synthesis study </h2>
<h1><strong>Grichener et al. 2023</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Aldana Grichener
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2302.06663.pdf">2302.06663</a></p>
<!-- Description -->
<p>
We perform population synthesis of massive binaries to study the mergers ofneutron stars (NSs) and black holes (BHs) with the cores of their giantsecondaries during common envelope evolution (CEE). We use different values ofthe efficiency parameter $\alpha_{\rm CE}$ in the framework of the energyformalism for traditional CEE ($\alpha_{\rm CE} \leq 1$) and includingadditional energy sources to unbind the envelope ($\alpha_{\rm CE} > 1$). Weconstrain the possible values of $\alpha_{\rm CE}$ by comparing the results ofour simulations with local rate densities of binary compact object mergers asinferred from gravitational waves observations. We find two primaryevolutionary pathways of binary systems that result in NS-core mergers, whileonly one of them can also lead to the merger of a BH with the core of the giantstar. We explore the zero age main sequence (ZAMS) statistical properties ofsystems that result in NS/BH-core mergers and find that the two evolutionarychannels correspond to a bimodal distribution of orbital separations. Weestimate the percentage of the mergers' event rates relative to core collapsesupernovae (CCSNe). We include the effect of mass accreted by the NS/BH duringCEE in a separate set of simulations and find it does not affect the mergers'event rates.
</p>
</div>
</article>
<!-- Sá et al. 2022 -->
<article>
<header>
<h2 id="221102714" style="margin-bottom:0.5em"> Effects of a non-universal IMF and binary parameter correlations on compact binary mergers </h2>
<h1><strong>Sá et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
L. M. de Sá; A. Bernardo; R. R. A. Bachega; L. S. Rocha; J. E. Horvath
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2211.02714.pdf">2211.02714</a></p>
<!-- Description -->
<p>
Binary population synthesis provides a direct way of studying the effects ofdifferent choices of binary evolution models and initial parameterdistributions on present-day binary compact merger populations, which can thenbe compared to empirical properties such as observed merger rates. Samples ofzero-age main sequence binaries to be evolved by such codes are typicallygenerated from an universal IMF and simple, uniform, distributions for orbitalperiod $P$, mass ratio $q$ and eccentricity $e$. More recently, however,mounting observational evidence has suggested the non-universality of the IMFand the existence of correlations between binary parameters. In this study, weimplement a metallicity- and redshift-dependent IMF alongside correlateddistributions for $P$, $q$ and $e$ in order to generate representativepopulations of binaries at varying redshifts, which are then evolved with theCOMPAS code in order to study the variations in merger rates and overallpopulation properties.
</p>
</div>
</article>
<!-- Stevenson et al. 2022 -->
<article>
<header>
<h2 id="221005040" style="margin-bottom:0.5em"> Constraints on the contributions to the observed binary black hole population from individual evolutionary pathways in isolated binary evolution </h2>
<h1><strong>Stevenson et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Simon Stevenson; Teagan Clarke
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2210.05040.pdf">2210.05040</a></p>
<!-- Description -->
<p>
Gravitational waves from merging binary black holes can be used to shed lighton poorly understood aspects of massive binary stellar evolution, such as theevolution of massive stars (including their mass-loss rates), the commonenvelope phase, and the rate at which massive stars form throughout the cosmichistory of the Universe. In this paper we explore the \emph{correlated} impactof these phases on predictions for the merger rate and chirp mass distributionof merging binary black holes, aiming to identify possible degeneracies betweenmodel parameters. In many of our models, a large fraction (more than 70% ofdetectable binary black holes) arise from the chemically homogeneous evolutionscenario; these models tend to over-predict the binary black hole merger rateand produce systems which are on average too massive. Our preferred modelsfavour enhanced mass-loss rates for helium rich Wolf--Rayet stars, in tensionwith recent theoretical and observational developments. We identifycorrelations between the impact of the mass-loss rates of Wolf--Rayet stars andthe metallicity evolution of the Universe on the rates and properties ofmerging binary black holes. Based on the observed mass distribution, we arguethat the $\sim 10\%$ of binary black holes with chirp masses greater than $40$M$_\odot$ (the maximum predicted by our models) are unlikely to have formedthrough isolated binary evolution, implying a significant contribution (> 10%)from other formation channels such as dense star clusters or active galacticnuclei. Our models will enable inference on the uncertain parameters governingbinary evolution in the near future.
</p>
</div>
</article>
<!-- Son et al. -->
<article>
<header>
<h2 id="220913609" style="margin-bottom:0.5em"> No peaks without valleys: The stable mass transfer channel for gravitational-wave sources in light of the neutron star-black hole mass gap </h2>
<h1><strong>Son et al.</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
L. A. C. van Son; S. E. de Mink; M. Renzo; S. Justham; E. Zapartas; K. Breivik; T. Callister; W. M. Farr; C. Conroy
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2209.13609.pdf">2209.13609</a></p>
<!-- Description -->
<p>
Gravitational-wave (GW) detections are starting to reveal features in themass distribution of double compact objects. The lower end of the black hole(BH) mass distribution is especially interesting as few formation channelscontribute here and because it is more robust against variations in the cosmicstar formation than the high mass end. In this work we explore the stable masstransfer channel for the formation of GW sources with a focus on the low-massend of the mass distribution. We conduct an extensive exploration of theuncertain physical processes that impact this channel. We note that, forfiducial assumptions, this channel reproduces the peak at $\sim9\mathrm{M_{\odot}}$ in the GW-observed binary BH mass distribution remarkablywell, and predicts a cutoff mass that coincides with the upper edge of thepurported neutron star BH mass gap. The peak and cutoff mass are a consequenceof unique properties of this channel, namely (1) the requirement of stabilityduring the mass transfer phases, and (2) the complex way in which the finalcompact object masses scale with the initial mass. We provide an analyticalexpression for the cutoff in the primary component mass and show that thisadequately matches our numerical results. Our results imply that selectioneffects resulting from the formation channel alone can provide an explanationfor the purported neutron star--BH mass gap in GW detections. This provides analternative to the commonly adopted view that the gap emerges during BHformation.
</p>
</div>
</article>
<!-- Broekgaarden et al. 2022-->
<article>
<header>
<h2 id="211205763" style="margin-bottom:0.5em"> Impact of Massive Binary Star and Cosmic Evolution on Gravitational Wave Observations II: Double Compact Object Rates and Properties </h2>
<h1><strong>Broekgaarden et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Floor S. Broekgaarden; Edo Berger; Simon Stevenson; Stephen Justham; Ilya Mandel; Martyna Chruślińska; Lieke A. C. van Son; Tom Wagg; Alejandro Vigna-Gómez; Selma E. de Mink; Debatri Chattopadhyay; Coenraad J. Neijssel
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2112.05763.pdf">2112.05763</a></p>
<!-- Description -->
<p>
Making the most of the rapidly increasing population of gravitational-wavedetections of black hole (BH) and neutron star (NS) mergers requires comparingobservations with population synthesis predictions. In this work we investigatethe combined impact from the key uncertainties in population synthesismodelling of the isolated binary evolution channel: the physical processes inmassive binary-star evolution and the star formation history as a function ofmetallicity, $Z$, and redshift $z, \mathcal{S}(Z,z)$. Considering theseuncertainties we create 560 different publicly available model realizations andcalculate the rate and distribution characteristics of detectable BHBH, BHNS,and NSNS mergers. We find that our stellar evolution and $\mathcal{S}(Z,z)$variations can impact the predicted intrinsic and detectable merger rates byfactors $10^2$-$10^4$. We find that BHBH rates are dominantly impacted by$\mathcal{S}(Z,z)$ variations, NSNS rates by stellar evolution variations andBHNS rates by both. We then consider the combined impact from all uncertaintiesconsidered in this work on the detectable mass distribution shapes (chirp mass,individual masses and mass ratio). We find that the BHNS mass distributions arepredominantly impacted by massive binary-star evolution changes. For BHBH andNSNS we find that both uncertainties are important. We also find that the shapeof the delay time and birth metallicity distributions are typically dominatedby the choice of $\mathcal{S}(Z,z)$ for BHBH, BHNS and NSNS. We identifyseveral examples of robust features in the mass distributions predicted by all560 models, such that we expect more than 95% of BHBH detections to contain aBH $\gtrsim 8\,\rm{M}_{\odot}$ and have mass ratios $\lesssim 4$. Our workdemonstrates that it is essential to consider a wide range of allowed models tostudy double compact object merger rates and properties.
</p>
</div>
</article>
<!-- Stevenson et al. 2022 -->
<article>
<header>
<h2 id="221005040" style="margin-bottom:0.5em"> Constraints on the contributions to the observed binary black hole population from individual evolutionary pathways in isolated binary evolution </h2>
<h1><strong>Stevenson et al. 2022</strong><h1>
</header>
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<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Simon Stevenson; Teagan Clarke
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2210.05040.pdf">2210.05040</a></p>
<!-- Description -->
<p>
Gravitational waves from merging binary black holes can be used to shed lighton poorly understood aspects of massive binary stellar evolution, such as theevolution of massive stars (including their mass-loss rates), the commonenvelope phase, and the rate at which massive stars form throughout the cosmichistory of the Universe. In this paper we explore the \emph{correlated} impactof these phases on predictions for the merger rate and chirp mass distributionof merging binary black holes, aiming to identify possible degeneracies betweenmodel parameters. In many of our models, a large fraction (more than 70% ofdetectable binary black holes) arise from the chemically homogeneous evolutionscenario; these models tend to over-predict the binary black hole merger rateand produce systems which are on average too massive. Our preferred modelsfavour enhanced mass-loss rates for helium rich Wolf--Rayet stars, in tensionwith recent theoretical and observational developments. We identifycorrelations between the impact of the mass-loss rates of Wolf--Rayet stars andthe metallicity evolution of the Universe on the rates and properties ofmerging binary black holes. Based on the observed mass distribution, we arguethat the $\sim 10\%$ of binary black holes with chirp masses greater than $40$M$_\odot$ (the maximum predicted by our models) are unlikely to have formedthrough isolated binary evolution, implying a significant contribution (> 10%)from other formation channels such as dense star clusters or active galacticnuclei. Our models will enable inference on the uncertain parameters governingbinary evolution in the near future.
</p>
</div>
</article>
<!-- Wagg et al. 2021 -->
<article>
<header>
<h2 id="211113704" style="margin-bottom:0.5em"> Gravitational wave sources in our Galactic backyard: Predictions for BHBH, BHNS and NSNS binaries detectable with LISA </h2>
<h1><strong>Wagg et al. 2021</strong><h1>
</header>
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<div class="content">
<!-- Authors -->
<p>
<strong>Authors:</strong>
Tom Wagg; Floor S. Broekgaarden; Selma E. de Mink; Lieke A. C. van Son; Neige Frankel; Stephen Justham
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2111.13704.pdf">2111.13704</a></p>
<!-- Description -->
<p>
Future searches for gravitational waves from space will be sensitive todouble compact objects (DCOs) in our Milky Way. We present new simulations ofthe populations of double black holes (BHBHs), black hole neutron stars (BHNSs)and double neutron stars (NSNSs) that will be detectable by the plannedspace-based gravitational wave detector LISA. For our estimates, we use anempirically-informed model of the metallicity dependent star formation historyof the Milky Way. We populate it using an extensive suite of binarypopulation-synthesis predictions for varying assumptions relating to masstransfer, common-envelope, supernova kicks, remnant masses and wind mass lossphysics. For a 4(10)-year LISA mission, we predict between 30-370(50-550)detections over these variations, out of which 6-154(9-238) are BHBHs,2-198(3-289) are BHNSs and 3-35(4-57) are NSNSs. We discuss how the variationsin the physics assumptions alter the distribution of properties of thedetectable systems, even when the detection rates are unchanged. In particularwe discuss the observable characteristics such as the chirp mass, eccentricityand sky localisation and how the BHBH, BHNS and NSNS populations can bedistinguished, both from each other and from the more numerous double whitedwarf population. We further discuss the possibility of multi-messengerobservations of pulsar populations with the Square Kilometre Array (SKA) andassess the benefits of extending the LISA mission.
</p>
</div>
</article>
<!-- Kapil et al. 2022 -->
<article>
<header>
<h2 id="220909252" style="margin-bottom:0.5em"> Calibration of neutron star natal kick velocities to isolated pulsar observations </h2>
<h1><strong>Kapil et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Veome Kapil; Ilya Mandel; Emanuele Berti; Bernhard Müller
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2209.09252.pdf">2209.09252</a></p>
<!-- Description -->
<p>
Current prescriptions for supernova natal kicks in rapid binary populationsynthesis simulations are based on fits of simple functions to single pulsarvelocity data. We explore a new parameterization of natal kicks received byneutron stars in isolated and binary systems developed by Mandel & M\"uller,which is based on 1D and 3D supernova simulations and accounts for the physicalcorrelations between progenitor properties, remnant mass, and the kickvelocity. We constrain two free parameters in this model using very longbaseline interferometry velocity measurements of Galactic single pulsars. Wefind that the inferred values of natal kick parameters do not differsignificantly between single and binary evolution scenarios. The best-fitvalues of these parameters are $v_{\rm ns} = 520$ km s$^{-1}$ for the scalingpre-factor for neutron star kicks, and $\sigma_{\rm ns}=0.3$ for the fractionalstochastic scatter in the kick velocities.
</p>
</div>
</article>
<!-- van Son et al. 2022 -->
<article>
<header>
<h2 id="220903385" style="margin-bottom:0.5em"> The locations of features in the mass distribution of merging binary black holes are robust against uncertainties in the metallicity-dependent cosmic star formation history </h2>
<h1><strong>van Son et al. 2022</strong><h1>
</header>
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<!-- Authors -->
<p>
<strong>Authors:</strong>
L. A. C. van Son; S. E. de Mink; M. Chruslinska; C. Conroy; R. Pakmor; L. Hernquist
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2209.03385.pdf">2209.03385</a></p>
<!-- Description -->
<p>
New observational facilities are probing astrophysical transients such asstellar explosions and gravitational wave (GW) sources at ever increasingredshifts, while also revealing new features in source property distributions.To interpret these observations, we need to compare them to predictions fromstellar population models. Such models require the metallicity-dependent cosmicstar formation history ($\mathcal{S}(Z,z)$) as an input. Large uncertaintiesremain in the shape and evolution of this function. In this work, we propose asimple analytical function for $\mathcal{S}(Z,z)$. Variations of this functioncan be easily interpreted, because the parameters link to its shape in anintuitive way. We fit our analytical function to the star-forming gas of thecosmological TNG100 simulation and find that it is able to capture the mainbehaviour well. As an example application, we investigate the effect ofsystematic variations in the $\mathcal{S}(Z,z)$ parameters on the predictedmass distribution of locally merging binary black holes (BBH). Our mainfindings are: I) the locations of features are remarkably robust againstvariations in the metallicity-dependent cosmic star formation history, and II)the low mass end is least affected by these variations. This is promising as itincreases our chances to constrain the physics that governs the formation ofthese objects.
</p>
</div>
</article>
<!-- Vigna-Gómez et al. 2022 -->
<article>
<header>
<h2 id="220308478" style="margin-bottom:0.5em"> A binary origin for the first isolated stellar-mass black hole detected with astrometric microlensing </h2>
<h1><strong>Vigna-Gómez et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Alejandro Vigna-Gómez; Enrico Ramirez-Ruiz
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2203.08478.pdf">2203.08478</a></p>
<!-- Description -->
<p>
The Milky Way is believed to host hundreds of millions of quiescentstellar-mass black holes (BHs). In the last decade, some of these objects havebeen potentially uncovered via gravitational microlensing events. All thesedetections resulted in a degeneracy between the velocity and the mass of thelens. This degeneracy has been lifted, for the first time, with the recentastrometric microlensing detection of OB110462. However, two independentstudies reported very different lens mass for this event. Sahu et al. (2022)inferred a lens mass of 7.1 $\pm$ 1.3 Msun, consistent with a BH, while Lam etal. (2022) inferred 1.6-4.2 Msun, consistent with either a neutron star or aBH. Here, we study the landscape of isolated BHs formed in the field. Inparticular, we focus on the mass and center-of-mass speed of foursub-populations: isolated BHs from single-star origin, disrupted BHs ofbinary-star origin, main-sequence stars with a compact object companion, anddouble compact object mergers. Our model predicts that most ($\gtrsim$ 50%)isolated BHs in the Milky Way are of binary origin. Moreover, the origin oflow-speed (< 50 km/s) isolated BHs depends on their mass: at least $\approx$70% of low-mass ($\lesssim$ 10 Msun) BHs are from binary origin. Under theassumption that OB110462 is a free-floating compact object, we conclude that itis more likely to be a BH originally belonging to a binary system. Our resultssuggest that low-speed BH microlensing events can be useful to understandbinary evolution of massive stars in the Milky Way.
</p>
</div>
</article>
<!-- Broekgaarden et al. 2022 -->
<article>
<header>
<h2 id="220501693" style="margin-bottom:0.5em"> Signatures of mass ratio reversal in gravitational waves from merging binary black holes </h2>
<h1><strong>Broekgaarden et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Floor S. Broekgaarden; Simon Stevenson; Eric Thrane
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2205.01693.pdf">2205.01693</a></p>
<!-- Description -->
<p>
The spins of merging binary black holes offer insights into their formationhistory. Recently it has been argued that in isolated binary evolution of twomassive stars the firstborn black hole is slowly rotating, whilst theprogenitor of the second-born black hole can be tidally spun up if the binaryis tight enough. Naively, one might therefore expect that only the less massiveblack hole in merging binaries exhibits non-negligible spin. However, if themass ratio of the binary is "reversed" (typically during the first masstransfer episode), it is possible for the tidally spun up second-born to becomethe more massive black hole. We study the properties of such mass-ratioreversed (MRR) binary black hole mergers using a large set of 560 populationsynthesis models. We find that the more massive black hole is formed second in$\gtrsim 70\%$ of binary black holes observable by LIGO, Virgo, and KAGRA formost model variations we consider, with typical total masses $\gtrsim 20$M$_{\odot}$ and mass ratios $q = m_2 / m_1 \sim 0.7$ (where $m_1 > m_2$). Theformation history of these systems typically involves only stable mass transferepisodes. The second-born black hole has non-negligible spin ($\chi > 0.05$) inup to $25\%$ of binary black holes, with among those the more (less) massiveblack hole spinning in $0\%$--$80\%$ ($20\%$--$100\%$) of cases, varyinggreatly in our models. We discuss our models in the context of several observedgravitational-wave events and the observed mass ratio - effective spincorrelation.
</p>
</div>
</article>
<!-- Stevenson et al. 2022 -->
<article>
<header>
<h2 id="220503989" style="margin-bottom:0.5em"> Wide binary pulsars from electron-capture supernovae </h2>
<h1><strong>Stevenson et al. 2022</strong><h1>
</header>
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<p>
<strong>Authors:</strong>
Simon Stevenson; Reinhold Willcox; Alejandro Vigna-Gomez; Floor Broekgaarden
<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong> <a href="https://arxiv.org/pdf/2205.03989.pdf">2205.03989</a></p>
<!-- Description -->
<p>
Neutron stars receive velocity kicks at birth in supernovae. Those formed inelectron-capture supernovae from super asymptotic giant branch stars -- thelowest mass stars to end their lives in supernovae -- may receive significantlylower kicks than typical neutron stars. Given that many massive stars aremembers of wide binaries, this suggests the existence of a population oflow-mass ($1.25 < M_\mathrm{psr} / $M$_\odot < 1.3$), wide ($P_\mathrm{orb}\gtrsim 10^{4}$\,day), eccentric ($e \sim 0.7$), unrecycled ($P_\mathrm{spin}\sim 1$\,s) binary pulsars. The formation rate of such binaries is sensitive tothe mass range of (effectively) single stars leading to electron capturesupernovae, the amount of mass lost prior to the supernova, and the magnitudeof any natal kick imparted on the neutron star. We estimate that one suchbinary pulsar should be observable in the Milky Way for every 10,000 isolatedpulsars, assuming that the width of the mass range of single stars leading toelectron-capture supernovae is $\lesssim 0.2$\,M$_\odot$, and that neutronstars formed in electron-capture supernovae receive typical kicks less than10\,km s$^{-1}$. We have searched the catalog of observed binary pulsars, butfind no convincing candidates that could be formed through this channel,consistent with this low predicted rate. Future observations with the SquareKilometre Array may detect this rare sub-class of binary pulsar and providestrong constraints on the properties of electron-capture supernovae and theirprogenitors.
</p>
</div>
</article> <!-- Chattopadhyay et al. 2022 -->
<article>
<header>
<h2 id="220305850" style=
"margin-bottom:0.5em">Modelling
the formation of the first two
neutron star-black hole
mergers, GW200105 and GW200115:
metallicity, chirp masses and
merger remnant spins</h2>
<h1><strong>Chattopadhyay et
al. 2022</strong>
</h1>
</header>
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"collapsible">Details</button>
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<!-- Authors -->
<p><strong>Authors:</strong>
Debatri Chattopadhyay; Simon
Stevenson; Floor Broekgaarden;
Fabio Antonini; Krzysztof
Belczynski<br>
<!-- <strong>Journal:</strong> <a href="website.com">JOURNAL</a><br> -->
<strong>arXiv:</strong>
<a href=
"https://arxiv.org/pdf/2203.05850.pdf">
2203.05850</a></p>
<!-- Description -->
<p>The two neutron star-black
hole mergers (GW200105 and
GW200115) observed
ingravitational waves by
advanced LIGO and Virgo, mark
the first ever discoveryof such
binaries in nature. We study
these two neutron star-black
hole systemsthrough isolated
binary evolution, using a grid
of population synthesis
models.Using both mass and spin
observations (chirp mass,
effective spin and remnantspin)
of the binaries, we probe their
different possible formation
channels indifferent
metallicity environments. Our
models only support LIGO data
whenassuming the black hole is
non spinning. Our results show
a strong preferencethat
GW200105 and GW200115 formed
from stars with sub-solar
metallicities$Z\lesssim 0.005$.
Only two metal-rich ($Z=0.02$)
models are in agreement
withGW200115. We also find that
chirp mass and remnant spins
jointly aid inconstraining the
models, whilst the effective
spin parameter does not add
anyfurther information. We also
present the observable (i.e.
post selectioneffects) median
values of spin and mass
distribution from all our
models, whichmaybe used as a
reference for future mergers.
Further, we show that the
remnantspin parameter
distribution exhibits
distinguishable features in
differentneutron star-black
hole sub-populations. We find
that non-spinning, first
bornblack holes dominate
significantly the merging
neutron star-black
holepopulation, ensuring
electromagnetic counterparts to
such mergers a rareaffair.</p>
</div>
</article>
<!-- COMPAS et al. 2021 (v3) -->
<article>
<header>
<h2 id="210910352v3" style=
"margin-bottom:0.5em">Rapid
stellar and binary population
synthesis with COMPAS</h2>
<h1><strong>COMPAS et al. 2021
(v3)</strong>
</h1>
</header>
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"collapsible">Details</button>
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<!-- Authors -->
<p><strong>Authors:</strong>
Team COMPAS; Jeff Riley; Poojan
Agrawal; Jim W. Barrett;
Kristan N. K. Boyett; Floor S.
Broekgaarden; Debatri
Chattopadhyay; Sebastian M.
Gaebel; Fabian Gittins; Ryosuke
Hirai; George Howitt; Stephen