We show how LIGO is expected to detect coalescing binary black holes at z>1 that are lensed by the intervening galaxy population. Gravitational magnification, μ, strengthens gravitational-wave ...signals by μ without altering their frequencies, which if unrecognized leads to an underestimate of the event redshift and hence an overestimate of the binary mass. High magnifications can be reached for coalescing binaries, because the region of intense gravitational-wave emission during coalescence is so small (∼100 km), permitting very close projections between lensing caustics and gravitational-wave events. Our simulations use the current LIGO event-based mass function and incorporate accurate waveforms convolved with the LIGO power spectral density. Importantly, we include the detection dependence on sky position and orbital orientation, which for the LIGO configuration translates into a wide spread in observed redshifts and chirp masses. Currently, we estimate a detectable rate of lensed events 0.06−0.02+0.02 yr−1 that rises to 5−3+5 yr−1 at LIGO design sensitivity limit, depending on the high redshift rate of black hole coalescence.
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Clouds of ultralight bosons-such as axions-can form around a rapidly spinning black hole, if the black hole radius is comparable to the bosons' wavelength. The cloud rapidly extracts angular momentum ...from the black hole, and reduces it to a characteristic value that depends on the boson's mass as well as on the black hole mass and spin. Therefore, a measurement of a black hole mass and spin can be used to reveal or exclude the existence of such bosons. Using the black holes released by LIGO and Virgo in their GWTC-2, we perform a simultaneous measurement of the black hole spin distribution at formation and the mass of the scalar boson. We find that the data strongly disfavor the existence of scalar bosons in the mass range between 1.3×10^{-13} and 2.7×10^{-13} eV. Our mass constraint is valid for bosons with negligible self-interaction, that is, with a decay constant f_{a}≳10^{14} GeV. The statistical evidence is mostly driven by the two binary black holes systems GW190412 and GW190517, which host rapidly spinning black holes. The region where bosons are excluded narrows down if these two systems merged shortly (∼10^{5} yr) after the black holes formed.
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Gravitational waves may be one of the few direct observables produced by ultralight bosons, conjectured dark matter candidates that could be the key to several problems in particle theory, ...high-energy physics and cosmology. These axionlike particles could spontaneously form "clouds" around astrophysical black holes, leading to potent emission of continuous gravitational waves that could be detected by instruments on the ground and in space. Although this scenario has been thoroughly studied, it has not been yet appreciated that both types of detector may be used in tandem (a practice known as "multibanding"). In this paper, we show that future gravitational-wave detectors on the ground and in space will be able to work together to detect ultralight bosons with masses 25 ≲ μ/(10−15 eV) ≲ 500. In detecting binary-black-hole inspirals, the LISA space mission will provide crucial information enabling future ground-based detectors, like Cosmic Explorer or Einstein Telescope, to search for signals from boson clouds around the individual black holes in the observed binaries. We lay out the detection strategy and, focusing on scalar bosons, chart the suitable parameter space. We study the impact of ignorance about the system's history, including cloud age and black hole spin. We also consider the tidal resonances that may destroy the boson cloud before its gravitational signal becomes detectable by a ground-based follow-up. Finally, we show how to take all of these factors into account, together with uncertainties in the LISA measurement, to obtain boson mass constraints from the ground-based observation facilitated by LISA.
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Gravitational waves emitted by coalescing compact objects carry information about the spin of the individual bodies. However, with present detectors only the mass-weighted combination of the ...components of the spin along the orbital angular momentum can be measured accurately. This quantity, the effective spin ?eff, is conserved up to at least the second post-Newtonian order. The measured distribution of ?eff values from a population of detected binaries, and in particular whether this distribution is symmetric about zero, encodes valuable information about the underlying compact-binary formation channels. In this paper we focus on two important complications of using the effective spin to study astrophysical population properties: (i) an astrophysical distribution for ?eff values which is symmetric does not necessarily lead to a symmetric distribution for the detected effective spin values, leading to a selection bias; and (ii) the posterior distribution of ?eff for individual events is asymmetric and it cannot usually be treated as a Gaussian. We find that the posterior distributions for ?eff systematically show fatter tails toward larger positive values, unless the total mass is large or the mass ratio m2/m1 is smaller than ?1/2. Finally we show that uncertainties in the measurement of ?eff are systematically larger when the true value is negative than when it is positive. All these factors can bias astrophysical inference about the population when we have more than ?100 events and should be taken into account when using gravitational-wave measurements to characterize astrophysical populations.
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Ultralight bosons can form clouds around rotating black holes if their Compton wavelength is comparable to the black hole size. The boson cloud spins down the black hole through a process called ...superradiance, lowering the black hole spin to a characteristic spin determined by the boson mass and the black hole mass. It has been suggested that spin measurements of the black holes detected by ground-based gravitational-wave detectors can be used to constrain the mass of ultralight bosons. Unfortunately, a measurement of the individual black hole spins is often uncertain, resulting in inconclusive results. Instead, we use hierarchical Bayesian inference to combine information from multiple gravitational-wave sources and to obtain stronger constraints. We show that hundreds of high signal-to-noise ratio gravitational-wave detections are enough to exclude (confirm) the existence of noninteracting bosons in the mass range 10−13,3×10−12 eV (10−13,10−12 eV). The precise number depends on the distribution of black hole spins at formation and the mass of the boson.
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Abstract
Third-generation (3G) gravitational-wave detectors will be able to observe binary black hole mergers (BBHs) up to a redshift of ∼30. This gives unprecedented access to the formation and ...evolution of BBHs throughout cosmic history. In this paper, we consider three subpopulations of BBHs originating from the different evolutionary channels: isolated formation in galactic fields, dynamical formation in globular clusters, and mergers of black holes formed from Population III (Pop III) stars at very high redshift. Using input from population synthesis analyses, we create 2 months of simulated data of a network of 3G detectors made of two Cosmic Explorers and one Einstein Telescope consisting of ∼16,000 field and cluster BBHs, as well as ∼400 Pop III BBHs. First, we show how one can use a nonparametric model to infer the existence and characteristics of a primary and secondary peak in the merger rate distribution as a function of redshift. In particular, the location and height of the secondary peak around
z
≈ 12, arising from the merger of Pop III remnants, can be constrained at the
level (95% credible interval). Then we perform a modeled analysis using phenomenological templates for the merger rates of the three subpopulations and extract the branching ratios and characteristic parameters of the merger rate densities of the individual formation channels. With this modeled method, the uncertainty on the measurement of the fraction of Pop III BBHs can be improved to ≲10%, while the ratio between field and cluster BBHs can be measured with an uncertainty of ∼100%.
A measurement of the history of cosmic star formation is central to understanding the origin and evolution of galaxies. The measurement is extremely challenging using electromagnetic radiation: ...significant modeling is required to convert luminosity to mass, and to properly account for dust attenuation, for example. Here we show how detections of gravitational waves from inspiraling binary black holes made by proposed third-generation detectors can be used to measure the star formation rate (SFR) of massive stars with high precision up to redshifts of ∼10. Depending on the time-delay model, the predicted detection rates ranges from ∼2310 to ∼56,740 per month with the current measurement of local merger rate density. With 30,000 detections, parameters describing the volumetric SFR can be constrained at the few percent level, and the volumetric merger rate can be directly measured to 3% at z ∼ 2. Given a parameterized SFR, the characteristic delay time between binary formation and merger can be measured to ∼60%.
Abstract
The possible existence of primordial black holes in the stellar-mass window has received considerable attention because their mergers may contribute to current and future gravitational-wave ...detections. Primordial black hole mergers, together with mergers of black holes originating from Population III stars, are expected to dominate at high redshifts (
z
≳ 10). However, the primordial black hole merger rate density is expected to rise monotonically with redshift, while Population III mergers can only occur after the birth of the first stars. Next-generation gravitational-wave detectors such as the Cosmic Explorer (CE) and Einstein Telescope (ET) can access this distinctive feature in the merger rates as functions of redshift, allowing for direct measurement of the abundance of the two populations and hence for robust constraints on the abundance of primordial black holes. We simulate four months’ worth of data observed by a CE-ET detector network and perform hierarchical Bayesian analysis to recover the merger rate densities. We find that if the universe has no primordial black holes with masses of
(
10
M
⊙
)
, the projected upper limit on their abundance
f
PBH
as a fraction of dark matter energy density may be as low as
f
PBH
∼
(
10
−
5
)
, about two orders of magnitude lower than the current upper limits in this mass range. If instead
f
PBH
≳ 10
−4
, future gravitational-wave observations would exclude
f
PBH
= 0 at the 95% credible interval.
Advanced LIGO and Virgo have so far detected gravitational waves from 10 binary black hole mergers (BBH) and 1 binary neutron star merger (BNS). In the future, we expect the detection of many more ...marginal sources, since compact binary coalescences detectable by advanced ground-based instruments are roughly distributed uniformly in comoving volume. In this paper we simulate weak signals from compact binary coalescences of various morphologies and optimal network signal-to-noise ratios (henceforth SNRs), and analyze if and to which extent their parameters can be measured by advanced LIGO and Virgo in their third observing run. We show that subthreshold binary neutron stars, with SNRs below 12 (10) yield uncertainties in their sky position larger than 400 (700) deg2 (90% credible interval). The luminosity distance, which could be used to measure the Hubble constant with standard sirens, has relative uncertainties larger than 40% for BNSs and neutron star black hole mergers. For sources with SNRs below 8, it is not uncommon that the extrinsic parameters, sky position and distance, cannot be measured. Next, we look at the intrinsic parameters, masses and spins. We show that the detector-frame chirp mass can sometimes be measured with uncertainties below 1% even for sources at SNRs of 6, although multimodality is not uncommon and can significantly broaden the posteriors. The effective inspiral spin is best measured for neutron star black hole mergers, for which the uncertainties can be as low as ∼ 0.08 ( ∼ 0.2 ) at SNR 12 (8). The uncertainty is higher for systems with comparable component masses or lack of spin precession.
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Abstract
Hierarchical analysis of binary black hole (BBH) detections by the Advanced LIGO and Virgo detectors has offered an increasingly clear picture of their mass, spin, and redshift ...distributions. Fully understanding the formation and evolution of BBH mergers will require not just the characterization of these marginal distributions, but the discovery of any correlations that exist between the properties of BBHs. Here, we hierarchically analyze the ensemble of BBHs discovered by LIGO and Virgo with a model that allows for intrinsic correlations between their mass ratios
q
and effective inspiral spins
χ
eff
. At 98.7% credibility, we find that the mean of the
χ
eff
distribution varies as a function of
q
, such that more unequal-mass BBHs exhibit systematically larger
χ
eff
. We find a Bayesian odds ratio of 10.5 in favor of a model that allows for such a correlation over one that does not. Finally, we use simulated signals to verify that our results are robust against degeneracies in the measurements of
q
and
χ
eff
for individual events. While many proposed astrophysical formation channels predict some degree correlation between spins and mass ratio, these predicted correlations typically act in an opposite sense to the trend we observationally identify in the data.
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