arXiv subjects

Matthew Benacquista

Publications and source records attributed to Matthew Benacquista.

13 recordsLinked to original sources

arXiv2023

Isolated and dynamical black hole mergers with \texttt{B-POP}: the role of star formation and dynamics, star cluster evolution, natal kicks, mass and spins, and hierarchical mergers

The current interpretation of LIGO--Virgo--KAGRA data suggests that the primary mass function of merging binary black holes (BBHs) at redshift $z\lesssim 1$ contains multiple structures, while spins are relatively low. Theoretical models of BBH formation in different environments can provide a key to interpreting the population of observed mergers, but they require the simultaneous treatment of stellar evolution and dynamics, galaxy evolution, and general relativity. We present \texttt{B-POP}, a population synthesis tool to model BBH mergers formed in the field or via dynamical interactions in young, globular, and nuclear clusters. Using \texttt{B-POP}, we explore how BH formation channels, star cluster evolution, hierarchical mergers, and natal BH properties affect the population of BBH mergers. We find that the primary mass distribution of BBH mergers extends beyond $M_1 \simeq 200\,{}$ M$_\odot$, and the effective spin parameter distribution hints at different natal spins for single and binary BHs. Observed BBHs can be interpreted as members of a mixed population comprised of $\sim 34\% \,{}(66\%)$ isolated (dynamical) BBHs, with the latter likely dominating at redshift $z>1$. Hierarchical mergers constitute the $4.6-7.9\%$ of all mergers in the reference model, dominating the primary mass distribution beyond $M_1 > 65\,{}$ M$_\odot$. The inclusion of cluster mass-loss and expansion causes an abrupt decrease in the probability for mergers beyond the third generation to occur. Considering observational biases, we find that $2.7-7.5\%$ of mock mergers involve intermediate-mass black hole (IMBH) seeds formed via stellar collisions. Comparing this percentage to observed values will possibly help us to constrain IMBH formation mechanisms.

astro-ph.GA↗

arXiv2020

Fingerprints of binary black hole formation channels encoded in the mass and spin of merger remnants

Binary black holes (BBHs) are thought to form in different environments, including the galactic field and (globular, nuclear, young and open) star clusters. Here, we propose a method to estimate the fingerprints of the main BBH formation channels associated with these different environments. We show that the metallicity distribution of galaxies in the local Universe along with the relative amount of mergers forming in the field or in star clusters determine the main properties of the BBH population. Our fiducial model predicts that the heaviest merger to date, GW170729, originated from a progenitor that underwent 2--3 merger events in a dense star cluster, possibly a galactic nucleus. The model predicts that at least one merger remnant out of 100 BBH mergers in the local Universe has mass $90 < M_{\rm rem}/ {\rm ~M}_\odot \leq{} 110$, and one in a thousand can reach a mass as large as $M_{\rm rem} \gtrsim 250$ M$_\odot$. Such massive black holes would bridge the gap between stellar-mass and intermediate-mass black holes. The relative number of low- and high-mass BBHs can help us unravelling the fingerprints of different formation channels. Based on the assumptions of our model, we expect that isolated binaries are the main channel of BBH merger formation if $\sim 70\%$ of the whole BBH population has remnants masses $<50$ M$_\odot$, whereas $\gtrsim{}6$\% of remnants with masses $>75$ M$_\odot$ point to a significant sub-population of dynamically formed BBH binaries.

astro-ph.GA↗

arXiv2018

Using final black hole spins and masses to infer the formation history of the observed population of gravitational wave sources

In this paper we propose a novel technique to constrain the progenitor binary black hole (BBH) formation history using the remnant masses and spins of merged black holes (BHs). Exploring different models, we found that dynamically formed BBHs are distributed differently in the mass-spin plane than those that have formed in isolation. Stellar evolution recipes crucially affect the remnant mass distribution, suggesting that future efforts should be devoted to finding a common way of modelling the evolutionary phases of single and binary stars. Our simple approach has allowed us to place weak constraints on the origin of the presently observed population of merged BHs, although with high uncertainties. Our results show that the fingerprints of different BBH formation channels will emerge as soon as LIGO detects more than $\sim 10^2$ merger events. This work provides a way of thinking that can be easily used both by people working on isolated and on dynamical BBH formation and evolution.

astro-ph.GA↗

arXiv2017

Double neutron stars: merger rates revisited

We revisit double neutron star (DNS) formation in the classical binary evolution scenario in light of the recent LIGO/Virgo DNS detection (GW170817). The observationally estimated Galactic DNS merger rate of $R_{\rm MW}=21^{+28}_{-14}$ Myr$^{-1}$, based on 3 Galactic DNS systems, fully supports our standard input physics model with $R_{\rm MW} =24$ Myr$^{-1}$. This estimate for the Galaxy translates in a non-trivial way (due to cosmological evolution of progenitor stars in chemically evolving Universe) into a local ($z\approx0$) DNS merger rate density of $R_{\rm local}=48$ Gpc$^{-3}$yr$^{-1}$, which {\em is not} consistent with the current LIGO/Virgo DNS merger rate estimate ($1540^{+3200}_{-1220}$ Gpc$^{-3}$yr$^{-1}$). Within our study of the parameter space we find solutions that allow for DNS merger rates as high as $R_{\rm local} \approx 600^{+600}_{-300}$ Gpc$^{-3}$yr$^{-1}$ which are thus consistent with the LIGO/Virgo estimate. However, our corresponding BH-BH merger rates for the models with high DNS merger rates exceed the current LIGO/Virgo estimate of local BH-BH merger rate ($12$-$213$ Gpc$^{-3}$yr$^{-1}$). Apart from being particularly sensitive to the common envelope treatment, DNS merger rates are rather robust against variations of several of the key factors probed in our study (e.g. mass transfer, angular momentum loss, natal kicks). This might suggest that either common envelope development/survival works differently for DNS ($\sim$ 10-20 Msun stars) than for BH-BH ($\sim$ 40-100 Msun stars) progenitors, or high BH natal kicks are needed to meet observational constraints for both types of binaries. Note that our conclusion is based on a limited number of (21) evolutionary models and is valid only within this particular DNS and BH-BH isolated binary formation scenario.

astro-ph.HE↗

arXiv2016

GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaboration

We present the results of the optical follow-up conducted by the TOROS collaboration of the first gravitational-wave event GW150914. We conducted unfiltered CCD observations (0.35-1 micron) with the 1.5-m telescope at Bosque Alegre starting ~2.5 days after the alarm. Given our limited field of view (~100 square arcmin), we targeted 14 nearby galaxies that were observable from the site and were located within the area of higher localization probability. We analyzed the observations using two independent implementations of difference-imaging algorithms, followed by a Random-Forest-based algorithm to discriminate between real and bogus transients. We did not find any bona fide transient event in the surveyed area down to a 5-sigma limiting magnitude of r=21.7 mag (AB). Our result is consistent with the LIGO detection of a binary black hole merger, for which no electromagnetic counterparts are expected, and with the expected rates of other astrophysical transients.

astro-ph.HE↗

arXiv2014

Prospects for Detection of Extragalactic Stellar Black Hole Binaries in the Nearby Universe

Stellar mass black hole binaries have individual masses between 10-80 solar masses. These systems may emit gravitational waves at frequencies detectable at Megaparsec distances by space-based gravitational wave observatories. In a previous study, we determined the selection effects of observing these systems with detectors similar to the Laser Interferometer Space Antenna by using a generated population of binary black holes that covered a reasonable parameter space and calculating their signal-to-noise ratio. We further our study by populating the galaxies in our nearby (less than 30 Mpc) universe with binary black hole systems drawn from a distribution found in the Synthetic Universe to ultimately investigate the likely event rate of detectable binaries from galaxies in the nearby universe.

gr-qc↗

arXiv2011

Detecting Double Degenerate Progenitors of SNe Ia with LISA

The Galactic population of close white dwarf binaries is expected to provide the largest number of gravitational wave sources for low frequency detectors such as the Laser Interferometer Space Antenna (LISA). Current data analysis techniques have demonstrated the capability of resolving on the order of $10^4$ white dwarf binaries from a 2 year observation. Resolved binaries are either at high frequencies or large amplitudes. Such systems are more likely to be high-mass binaries, a subset of which will be progenitors of SNe Ia in the double degenerate scenario. We report on results of a study of the properties of resolved binaries using a population synthesis model of the Galactic white dwarf binaries and a LISA data analysis algorithm using Mock LISA Data Challenge tools.

astro-ph.SR↗

arXiv2011

Tidal Perturbations to the Gravitational Inspiral of J0651+2844

The recently discovered J0651+2844 is a detached, eclipsing white dwarf binary with an orbital period of 765 s. We investigate the prospects for the detection of gravitational radiation from this system and estimate the effect of the tidal deformation of the low-mass component on the period evolution of the system. Because of the high inclination of the system, the amplitude of the gravitational waves at Earth will be as much as a factor of two lower than that from an optimally oriented system. The dominant contribution of tidal corrections to the period evolution comes from the increase in rotational energy of the components as they spin up to remain tied to the orbital period. This contribution results in an advance of the timing of the eclipses by an additional 0.3 s after one year.

astro-ph.SR↗

arXiv2010

Double Compact Objects as Low-frequency Gravitational Wave Sources

We study the Galactic field population of double compact objects (NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with LISA at low gravitational-wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contribution from the disk, bulge and halo. Although the Galaxy hosts 10^5 double compact object binaries emitting low-frequency gravitational waves, only a handful of these objects in the disk will be detectable with LISA, but none from the halo or bulge. This is because the bulk of these binaries are NS-NS systems with high eccentricities and long orbital periods (weeks/months) causing inefficient signal accumulation (small number of signal bursts at periastron passage in 1 yr of LISA observations) rendering them undetectable in the majority of these cases. We adopt two evolutionary models that differ in their treatment of the common envelope phase that is a major (and still mostly unknown) process in the formation of close double compact objects. Depending on the adopted evolutionary model, our calculations indicate the likely detection of about 4 NS-NS binaries and 2 BH-BH systems (model A; likely survival of progenitors through CE) or only a couple of NS-NS binaries (model B; suppression of the double compact object formation due to CE mergers).

astro-ph↗

arXiv2009

Triplets of supermassive black holes: Astrophysics, Gravitational Waves and Detection

Supermassive black holes (SMBHs) found in the centers of many galaxies have been recognized to play a fundamental active role in the cosmological structure formation process. In hierarchical formation scenarios, SMBHs are expected to form binaries following the merger of their host galaxies. If these binaries do not coalesce before the merger with a third galaxy, the formation of a black hole triple system is possible. Numerical simulations of the dynamics of triples within galaxy cores exhibit phases of very high eccentricity (as high as $e \sim 0.99$). During these phases, intense bursts of gravitational radiation can be emitted at orbital periapsis. This produces a gravitational wave signal at frequencies substantially higher than the orbital frequency. The likelihood of detection of these bursts with pulsar timing and the Laser Interferometer Space Antenna ({\it LISA}) is estimated using several population models of SMBHs with masses $\gtrsim 10^7 {\rm M_\odot}$. Assuming a fraction of binaries $\ge 0.1$ in triple system, we find that few to few dozens of these bursts will produce residuals $>1$ ns, within the sensitivity range of forthcoming pulsar timing arrays (PTAs). However, most of such bursts will be washed out in the underlying confusion noise produced by all the other 'standard' SMBH binaries emitting in the same frequency window. A detailed data analysis study would be required to assess resolvability of such sources. Implementing a basic resolvability criterion, we find that the chance of catching a resolvable burst at a one nanosecond precision level is 2-50%, depending on the adopted SMBH evolution model. On the other hand, the probability of detecting bursts produced by massive binaries (masses $\gtrsim 10^7\msun$) with {\it LISA} is negligible.

astro-ph.CO↗

arXiv2008

Contribution of Compact Mass Transferring Systems to the Galactic Gravitational Wave Background

Compact object binaries, mostly double with dwarfs, are believed to be a potential source of confusion-limited noise for the Laser Interferometer Space Antenna (LISA). In a specific frequency range, this noise may rise above the instrumental noise sources and hence hinder detection of other types of signals, e.g. extreme mass ratio inspirals of stellar mass objects into supermassive black holes. In most previous studies only detached populations of compact object binaries have been considered. Here, we investigate the influence of Galactic populations of compact mass transferring binaries on the shape and strength of the LISA signal and compare our results with the signal for detached binaries only. Our population synthesis includes all binary systems containing two compact remnants. It is found that 99.5% of these systems are double white dwarfs, and therefore we consider only binaries consisting of two white dwarfs when calculating the LISA signal. We find that the mass transferring binaries contributing to the confusion limited noise dominate the population of LISA systems by number (60%), due to their long lifetimes (few Gyrs). However, due to the very specific physical properties of mass transferring systems, it is found that their contribution to the noise is negligible at low frequencies and detached systems will set the magnitude of the confusion-limited signal in this range. However, the mass transferring systems begin to dominate the signal at higher frequencies (f>6 mHz). The transition frequency at which the confusion limited regime becomes important is found at 4 mHz. The addition of mass transferring systems tends to slightly increase the transition frequency (from 3.5 to 4 mHz).

astro-ph↗

arXiv2008

The Contribution of Halo White Dwarf Binaries to the LISA Signal

Galactic double white dwarfs were postulated as a source of confusion limited noise for LISA, the future space-based gravitational wave observatory. Until very recently, the Galactic population consisted of a relatively well studied disk population, a somewhat studied smaller bulge population and a mostly unknown, but potentially large halo population. It has been argued that the halo population may produce a signal that is much stronger (factor of ~5 in spectral amplitude) than the disk population. However, this surprising result was not based on an actual calculation of a halo white dwarf population but was derived on (i) the assumption that one can extrapolate the halo population properties from those of the disk population and (ii) the postulated (unrealistically) high number of white dwarfs in the halo. We perform the first calculation of a halo white dwarf population using population synthesis models. Our comparison with the signal arising from double white dwarfs in the Galactic disk+bulge clearly shows that it is impossible for the double white dwarf halo signal to exceed that of the rest of the Galaxy. Using microlensing results to give an upper limit on the content of white dwarfs in the halo (~30 % baryonic mass in white dwarfs), our predicted halo signal is a factor of 10 lower than the disk+bulge signal. Even in the implausible case where all of the baryonic halo mass is found in white dwarfs, the halo signal does not become comparable to that of the disk+bulge, and thus would still have a negligible effect on the detection of other LISA sources.

astro-ph↗

arXiv2006

Relativistic Binaries in Globular Clusters

The galactic population of globular clusters are old, dense star systems, with a typical cluster containing $10^4 - 10^6$ stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct $N$-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

astro-ph↗