arXiv subjects

Daniel E. Holz

Publications and source records attributed to Daniel E. Holz.

At least 55 records · Page 3Linked to original sources

arXiv2021

Distance measures in gravitational-wave astrophysics and cosmology

We present quantities which characterize the sensitivity of gravitational-wave observatories to sources at cosmological distances. In particular, we introduce and generalize the horizon, range, response, and reach distances. These quantities incorporate a number of important effects, including cosmologically well-defined distances and volumes, cosmological redshift, cosmological time dilation, and rate density evolution. In addition, these quantities incorporate unique aspects of gravitational wave detectors, such as the variable sky sensitivity of the detectors and the scaling of the sensitivity with inverse distance. An online calculator (https://users.rcc.uchicago.edu/~dholz/gwc/) and python notebook (https://github.com/hsinyuc/distancetool) to determine GW distances are available. We provide answers to the question: "How far can gravitational-wave detectors hear?"

astro-ph.CO↗

arXiv2020

Direct Astrophysical Tests of Chiral Effective Field Theory at Supranuclear Densities

Recent observations of neutron stars with gravitational waves and X-ray timing provide unprecedented access to the equation of state (EoS) of cold dense matter at densities difficult to realize in terrestrial experiments. At the same time, predictions for the EoS with reliable uncertainty estimates from chiral effective field theory ($χ$EFT) bound our theoretical ignorance. In this work, we analyze astrophysical data using a nonparametric representation of the neutron-star EoS conditioned on $χ$EFT to directly constrain the underlying physical properties of the compact objects. We discuss how the data alone constrain the EoS at high densities when we condition on $χ$EFT at low densities. We also demonstrate how to exploit astrophysical data to directly test the predictions of $χ$EFT for the EoS up to twice nuclear saturation density, and estimate the density at which these predictions might break down. We find that the existence of massive pulsars, gravitational waves from GW170817, and NICER observations of PSR J0030+0451 favor $χ$EFT predictions for the EoS up to nuclear saturation density over a more agnostic analysis by as much as a factor of 7 for the quantum Monte Carlo (QMC) calculations used in this work. While $χ$EFT predictions using QMC are fully consistent with gravitational-wave data up to twice nuclear saturation density, NICER observations suggest that the EoS stiffens relative to these predictions at nuclear saturation density. Additionally, we marginalize over the uncertainty in the density at which $χ$EFT begins to break down, constraining the radius of a $1.4\,M_\odot$ neutron star to $R_{1.4}=11.40^{+1.38}_{-1.04}$ ($12.54^{+0.71}_{-0.63}$) km and the pressure at twice nuclear saturation density to $p(2n_\mathrm{sat})=14.2^{+18.1}_{-8.4}$ ($28.7^{+15.3}_{-15.0}$) MeV/fm$^3$ with massive pulsar and gravitational-wave (and NICER) data.

astro-ph.HE↗

arXiv2020

Minding the gap: GW190521 as a straddling binary

Models for black hole (BH) formation from stellar evolution robustly predict the existence of a pair-instability supernova (PISN) mass gap in the range $\sim50$ to $\sim120$ solar masses. This theoretical prediction is supported by the binary black holes (BBHs) of LIGO/Virgo's first two observing runs, whose component masses are well-fit by a power law with a maximum mass cutoff at $m_\mathrm{max}=40.8^{+11.8}_{-4.4}\,M_\odot$. Meanwhile, the BBH event GW190521 has a reported primary mass of $m_1=85^{+21}_{-14}\,M_\odot$, firmly above the inferred $m_\mathrm{max}$, and secondary mass $m_2=66^{+17}_{-18}\,M_\odot$. Rather than concluding that both components of GW190521 belong to a new population of mass-gap BHs, we explore the conservative scenario in which GW190521's secondary mass belongs to the previously-observed population of BHs. We replace the default priors on $m_1$ and $m_2$, which assume that BH detector-frame masses are uniformly distributed, with this population-informed prior on $m_2$, finding $m_2<48\,M_\odot$ at 90\% credibility. Moreover, because the total mass of the system is better constrained than the individual masses, the population prior on $m_2$ automatically increases the inferred $m_1$ to sit \emph{above} the gap (39\% for $m_1 > 120\,M_\odot$, or 25\% probability for $m_1>130\,M_\odot$). As long as the prior odds for a double-mass-gap BBH are smaller than $\sim 1:15$, it is more likely that GW190521 straddles the pair-instability gap. We argue that GW190521 may be the first example of a straddling binary black hole, composed of a conventional stellar mass BH and a BH from the ``far side' of the PISN mass gap.

astro-ph.HE↗

arXiv2020

Does Matter Matter? Using the mass distribution to distinguish neutron stars and black holes

Gravitational-wave detectors have opened a new window through which we can observe black holes (BHs) and neutron stars (NSs). Analyzing the 11 detections from LIGO/Virgo's first gravitational-wave catalog, GWTC-1, we investigate whether the power-law fit to the BH mass spectrum can also accommodate the binary neutron star (BNS) event GW170817, or whether we require an additional feature, such as a mass gap, in between the NS and BH populations. We find that with respect to the power-law fit to binary black hole (BBH) masses, GW170817 is an outlier at the 0.13\% level, suggesting a distinction between NS and BH masses. A single power-law fit across the entire mass range is in mild tension with: (a) the detection of one source in the BNS mass range ($\sim 1$--$2.5 \,M_\odot$), (b) the absence of detections in the "mass-gap" range ($\sim 2.5$--$5 \,M_\odot$), and (c) the detection of 10 sources in the BBH mass range ($\gtrsim 5 \,M_\odot$). Instead, the data favor models with a feature between NS and BH masses, including a mass gap (Bayes factor of 4.6) and a break in the power law, with a steeper slope at NS masses compared to BH masses (91\% credibility). We estimate the merger rates of compact binaries based on our fit to the global mass distribution, finding $\mathcal{R}_\mathrm{BNS} = 871^{+3015}_{-805} \ \mathrm{Gpc}^{-3} \ \mathrm{yr}^{-1}$ and $\mathcal{R}_\mathrm{BBH} = 47.5^{+57.9}_{-28.8} \ \mathrm{Gpc}^{-3} \ \mathrm{yr}^{-1}$. We conclude that, even in the absence of any prior knowledge of the difference between NSs and BHs, the gravitational-wave data alone already suggest two distinct populations of compact objects.

astro-ph.HE↗

arXiv2020

Cosmological Inference using Gravitational Wave Standard Sirens: A Mock Data Challenge

The observation of binary neutron star merger GW170817, along with its optical counterpart, provided the first constraint on the Hubble constant $H_0$ using gravitational wave standard sirens. When no counterpart is identified, a galaxy catalog can be used to provide the necessary redshift information. However, the true host might not be contained in a catalog which is not complete out to the limit of gravitational-wave detectability. These electromagnetic and gravitational-wave selection effects must be accounted for. We describe and implement a method to estimate $H_0$ using both the counterpart and the galaxy catalog standard siren methods. We perform a series of mock data analyses using binary neutron star mergers to confirm our ability to recover an unbiased estimate of $H_0$. Our simulations used a simplified universe with no redshift uncertainties or galaxy clustering, but with different magnitude-limited catalogs and assumed host galaxy properties, to test our treatment of both selection effects. We explore how the incompleteness of catalogs affects the final measurement of $H_0$, as well as the effect of weighting each galaxy's likelihood of being a host by its luminosity. In our most realistic simulation, where the simulated catalog is about three times denser than the density of galaxies in the local universe, we find that a 4.4\% measurement precision can be reached using galaxy catalogs with 50\% completeness and $\sim 250$ binary neutron star detections with sensitivity similar to that of Advanced LIGO's second observing run.

gr-qc↗

arXiv2020

Black Hole Coagulation: Modeling Hierarchical Mergers in Black Hole Populations

Data from the LIGO and Virgo detectors has confirmed that stellar-mass black holes can merge within a Hubble time, leaving behind massive remnant black holes. In some astrophysical environments such as globular clusters and AGN disks, it may be possible for these remnants to take part in further compact-object mergers, producing a population of hierarchically formed black holes. In this work, we present a parameterized framework for describing the population of binary black hole mergers, while self-consistently accounting for hierarchical mergers. The framework casts black holes as particles in a box which can collide based on an effective cross-section, but allows inputs from more detailed astrophysical simulations. Our approach is relevant to any population which is comprised of second or higher generation black holes, such as primordial black holes or dense cluster environments. We describe some possible inputs to this generic model and their effects on the black hole merger populations, and use the model to perform Bayesian inference on the catalog of black holes from LIGO and Virgo's first two observing runs. We find that models with a high rate of hierarchical mergers are disfavored, consistent with previous population analyses. Future gravitational-wave events will further constrain the inputs to this generic hierarchical merger model, enabling a deeper look into the formation environments of binary black holes.

astro-ph.HE↗

arXiv2020

Picky Partners: The Pairing of Component Masses in Binary Black Hole Mergers

We examine the relationship between individual black hole (BH) masses in merging binary black hole (BBH) systems. Analyzing the ten BBH detections from LIGO/Virgo's first two observing runs, we find that the masses of the component BHs comprising each binary are unlikely to be randomly drawn from the same underlying distribution. Instead, the two BHs of a given binary prefer to be of comparable mass. We show that it is $\sim 5$ times more likely that the component BHs in a given binary are always equal (to within 5\%) than that they are randomly paired. If we assume that the probability of a merger between two BHs scales with the mass ratio $q$ as $q^β$, so that $β=0$ corresponds to random pairings, we find $β>0$ is favored at credibility 0.987. By modeling the mass distribution, we find that the median mass ratio is $q_{50\%} = 0.91^{+0.05}_{-0.17}$ at 90\% credibility. While the pairing between BHs depends on their mass ratio, we find no evidence that it depends on the total mass of the system: it is $\sim 6$ times more likely that the pairing depends purely on the mass ratio than on the total mass. We predict that 99\% of BBHs detected by LIGO/Virgo will have mass ratios $q > 0.5$. We conclude that merging black holes do not form random pairings; instead they are selective about their partners, preferring to mate with black holes of a similar mass. The details of these selective pairings provide insight into the underlying formation channels of merging binaries.

astro-ph.HE↗

arXiv2020

The binary-host connection: astrophysics of gravitational wave binaries from their host galaxy properties

Gravitational waves produced from the merger of binary neutron stars (BNSs) are accompanied by electromagnetic counterparts, making it possible to identify the associated host galaxy. We explore how properties of the host galaxies relate to the astrophysical processes leading to the mergers. It is thought that the BNS merger rate within a galaxy at a given epoch depends primarily on the galaxy's star-formation history as well as the underlying merger time-delay distribution of the binary systems. The stellar history of a galaxy, meanwhile, depends on the cosmological evolution of the galaxy through time, and is tied to the growth of structure in the Universe. We study the hosts of BNS mergers in the context of structure formation by populating the Universe Machine simulations with gravitational-wave events~ according to a simple time-delay model. We find that different time-delay distributions predict different properties of the associated host galaxies, including the distributions of stellar mass, star-formation rate, halo mass, and local and large-scale clustering of hosts. BNSs that merge today with short delay times prefer to be in hosts that have high star-formation rates, while those with long delay times live in dense regions within massive halos that have low star formation. We show that with ${\mathcal O}(10)$ events from current gravitational-wave detector networks, it is possible to make preliminary distinctions between formation channels which trace stellar mass, halo mass, or star-formation rate. We also find that strategies to follow up gravitational-wave events with electromagnetic telescopes can be significantly optimized using the clustering properties of their hosts.

astro-ph.GA↗

arXiv2019

Counting on Short Gamma-Ray Bursts: Gravitational-Wave Constraints of Jet Geometry

The detection of GW170817 in gravitational waves and gamma rays revealed that short gamma-ray bursts are associated with the merger of neutron-stars. Gamma rays are thought to result from the formation of collimated jets, but the details of this process continue to elude us. One fundamental observable is the emission profile of the jet as a function of viewing angle. We present two methods to measure the effective angular width, $θ_B$, of short gamma-ray burst (sGRB) jets using gravitational wave and gamma-ray data, assuming all sGRBs have the same angular dependence for their luminosities. The first is a counting experiment, where we combine the known detection thresholds of the LIGO/Virgo and Fermi Gamma Ray Burst Monitor detectors to infer parameters of systems that are detected in gravitational waves. This method requires minimal knowledge about each event, beyond whether or not they were detected in gamma-rays. The second method uses additional information from the gravitational-wave and electromagnetic data to estimate parameters of the source, and thereby improve constraints on jet properties. Applying our methods to GW170817, we find only weak constraints on the sGRB luminosity profile, with statistical uncertainty dominating differences between models. We also analyze simulated events from future observing runs, and find that with 5 and 100 BNS detections, the counting method constrains the relative uncertainty in $θ_B$ to within 51% and 12%, respectively. Incorporating gravitational-wave parameter estimation would further tighten these constraints to 43% and 9.6%. In the limit of many detections, incorporating parameter estimation achieves only marginal improvements; we conclude that the majority of the information about jet structure comes from the relative sensitivities of gravitational-wave and gamma-ray detectors as encoded in simple counting experiments.

astro-ph.HE↗

arXiv2019

The Most Massive Binary Black Hole Detections and the Identification of Population Outliers

Advanced LIGO and Virgo detected ten binary black holes (BBHs) in their first two observing runs (O1 and O2). Analysis of these events found strong evidence for a dearth of BBHs with component masses greater than $\sim45 \ M_\odot$, as would be expected from a pair-instability mass gap. Meanwhile, a standalone analysis of the merger GW170729 found its primary mass $m_1 = {51.2^{+16.2}_{-11.0} \ M_\odot}$, with the majority of its posterior support at $m_1 > 45 \ M_\odot$. Although this appears to be in contradiction with the existence of a limit at $\sim45\ M_\odot$, we argue that individual events cannot be evaluated without reference to the entire population. When GW170729 is analyzed jointly with the rest of the detections, as part of a full hierarchical population analysis, its inferred primary mass tightens considerably, to $m_1 = {38.9^{+7.3}_{-4.5} \ M_\odot}$. For a large sample of events in the presence of noise, apparent outliers in the detected distribution are inevitable, even if the underlying population forbids outliers. We discuss methods of distinguishing between statistical fluctuations and population outliers using posterior predictive tests. Applying these tests to the primary mass distribution in O1 and O2, we find that the ten detections are consistent with even the simplest power-law plus maximum-mass model considered by the LVC. This supports the claim that GW170729 is not a population outlier. We also provide non-parametric constraints on the rate of high-mass mergers and conservatively bound the rate of mergers with $m_1 > 45 \ M_\odot$ at $2.8^{+5.4}_{-2.0}\%$ of the total merger rate. After 100 detections like those of O1 and O2 from a population with a maximum primary mass of $45 \, M_\odot$, it would be common for the most massive system to have an observed maximum-likelihood mass $m_1 \gtrsim 70 \, M_\odot$.

astro-ph.HE↗

arXiv2019

Nonparametric Inference of Neutron Star Composition, Equation of State, and Maximum Mass with GW170817

The detection of GW170817 in gravitational waves provides unprecedented constraints on the equation of state (EOS) of the ultra-dense matter within the cores of neutron stars (NSs). We extend the nonparametric analysis first introduced in Landry & Essick (2019), and confirm that GW170817 favors soft EOSs. We infer macroscopic observables for a canonical 1.4 $M_{\odot}$ NS, including the tidal deformability $Λ_{1.4} = 211^{+312}_{-137}$ ($491^{+216}_{-181}$) and radius $R_{1.4}= 10.86^{+2.04}_{-1.42}$ ($12.51^{+1.00}_{-0.88}$) km, as well as the maximum mass for nonrotating NSs, $M_{max} = 2.064^{+0.260}_{-1.34}$ ($2.017^{0.238}_{-0.087}$) $M_\odot$, with nonparametric priors loosely (tightly) constrained to resemble candidate EOSs from the literature. Furthermore, we find weak evidence that GW170817 involved at least one NS based on gravitational-wave data alone ($B^{NS}_{BBH}= 3.3 \pm 1.4$), consistent with the observation of electromagnetic counterparts. We also investigate GW170817's implications for the maximum spin frequency of millisecond pulsars, and find that the fastest known pulsar is spinning at more than 50% of its breakup frequency at 90% confidence. We additionally find modest evidence in favor of quark matter within NSs, and GW170817 favors the presence of at least one disconnected hybrid star branch in the mass--radius relation over a single stable branch by a factor of 2. Assuming there are multiple stable branches, we find a suggestive posterior preference for a sharp softening around nuclear density followed by stiffening around twice nuclear density, consistent with a strong first-order phase transition. While the statistical evidence in favor of new physics within NS cores remains tenuous with GW170817 alone, these tantalizing hints reemphasize the promise of gravitational waves for constraining the supranuclear EOS.

astro-ph.HE↗

arXiv2019

Black Hole Shadows, Photon Rings, and Lensing Rings

The presence of a bright "photon ring" surrounding a dark "black hole shadow" has been discussed as an important feature of the observational appearance of emission originating near a black hole. We clarify the meaning and relevance of these heuristics with analytic calculations and numerical toy models. The standard usage of the term "shadow" describes the appearance of a black hole illuminated from all directions, including from behind the observer. A backlit black hole casts a somewhat larger shadow. Neither shadow heuristic is particularly relevant to understanding the appearance of emission originating near the black hole, where the emission profile and gravitational redshift play the dominant roles in determining the observed size of the central dark area. A photon ring results from light rays that orbit near the black hole before escaping to infinity, where they arrive near a ring-shaped "critical curve" on the image plane. Although the brightness can become arbitrarily large near this critical curve in the case of optically thin emitting matter, we show that the enhancement is only logarithmic, and hence is of no relevance to present observations. For optically thin emission from a geometrically thin or thick disk, photons that make only a fraction of an orbit will generically give rise to a much wider "lensing ring," which is a demagnified image of the back of the disk, superimposed on top of the direct emission. The lensing ring is centered at a radius ~5% larger than the photon ring and its width is ~0.5-1M. It can be relatively brighter by a factor of 2-3 and thus could provide a significant feature in high resolution images. Nevertheless, the characteristic features of the observed image are dominated by the location and properties of the emitting matter near the black hole. We comment on the recent M87* Event Horizon Telescope observations and mass measurement.

astro-ph.HE↗

arXiv2019

Standard sirens with a running Planck mass

We consider the effect of a time-varying Planck mass on the propagation of gravitational waves (GWs). A running Planck mass arises naturally in several modified gravity theories, and here we focus on those that carry an additional dark energy field responsible for the late-time accelerated expansion of the universe, yet--like general relativity (GR)--propagate only two GW polarizations, both traveling at the speed of light. Because a time-varying Planck mass affects the amplitude of the GWs and therefore the inferred distance to the source, standard siren measurements of $H_0$ are degenerate with the parameter $c_M$ characterizing the time-varying Planck mass, where $c_M=0$ corresponds to GR with a constant Planck mass. The effect of non-zero $c_M$ will have a noticeable impact on GWs emitted by binary neutron stars (BNSs) at the sensitivities and distances observable by ground-based GW detectors such as advanced LIGO and A+, implying that standard siren measurements can provide joint constraints on $H_0$ and $c_M$. Assuming a $Λ$CDM evolution of the universe and taking Planck's measurement of $H_0$ as a prior, we find that GW170817 constrains $c_M = -9^{+21}_{-28}$ ($68.3\%$ credibility). We also discuss forecasts, finding that if we assume $H_0$ is known independently, then 100 BNS events detected by advanced LIGO can constrain $c_M$ to within $\pm0.9$. This is comparable to the current best constraints from cosmology. Similarly, for 100 LIGO A+ BNS detections, it is possible to constrain $c_M$ to $\pm0.5$. When analyzing joint $H_0$ and $c_M$ constraints we find that $\sim 400$ LIGO A+ events are needed to constrain $H_0$ to $1\%$ accuracy. Finally, we discuss the possibility of a nonzero value of $c_M$ biasing standard siren $H_0$ measurements from 100 LIGO A+ detections, and find that $c_M=+1.35$ could bias $H_0$ by 3-4$σ$ too low if we incorrectly assume $c_M=0$.

astro-ph.CO↗

arXiv2019

Calibrating gravitational-wave detectors with GW170817

The waveform of a compact binary coalescence is predicted by general relativity. It is therefore possible to directly constrain the response of a gravitational-wave (GW) detector by analyzing a signal's observed amplitude and phase evolution as a function of frequency. GW signals alone constrain the relative amplitude and phase between different frequencies within the same detector and between different detectors. We analyze GW170817's ability to calibrate the LIGO/Virgo detectors, finding a relative amplitude calibration precision of approximately $\pm20\%$ and relative phase precision of $\pm15^\circ$ (1-$σ$ uncertainty) between the LIGO Hanford and Livingston detectors. Incorporating additional information about the distance and inclination of the source from electromagnetic observations, the relative amplitude of the LIGO detectors can be tightened to $\sim\pm15\%$. We investigate the ability of future events to improve astronomical calibration. By simulating the cumulative uncertainties from an ensemble of detections, we find that with several hundred events with electromagnetic counterparts, or several thousand events without counterparts, we reach percent-level astronomical calibration. This corresponds to $\sim$5-10 years of operation at advanced LIGO and Virgo design sensitivity. It is to be emphasized that direct {\em in-situ}\/ measurements of detector calibration provide significantly higher precision than astronomical sources, and already constrain the calibration to a few percent in amplitude and a few degrees in phase. In this sense, our astronomical calibrators only corroborate existing calibration measurements. Nonetheless, astrophysical calibration may become an important corroboration of existing calibration methods, providing a completely independent constraint of potential systematics.

astro-ph.IM↗

arXiv2018

The cosmological impact of future constraints on $H_0$ from gravitational-wave standard sirens

Gravitational-wave standard sirens present a novel approach for the determination of the Hubble constant. After the recent spectacular confirmation of the method thanks to GW170817 and its optical counterpart, additional standard siren measurements from future gravitational-wave sources are expected to constrain the Hubble constant to high accuracy. At the same time, improved constraints are expected from observations of cosmic microwave background (CMB) polarization and from baryon acoustic oscillations (BAO) surveys. We explore the role of future standard siren constraints on $H_0$ in light of expected CMB+BAO data. Considering a $10$-parameters cosmological model, in which curvature, the dark energy equation of state, and the Hubble constant are unbounded by CMB observations, we find that a combination of future CMB+BAO data will constrain the Hubble parameter to $\sim 1.5 \%$. Further extending the parameter space to a time-varying dark energy equation of state, we find that future CMB+BAO constraints on $H_0$ are relaxed to $\sim 3.0 \%$. These accuracies are within reach of future standard siren measurements from the Hanford-Livingston-Virgo and the Hanford-Livingston-Virgo-Japan-India networks of interferometers, showing the cosmological relevance of these sources. If future gravitational-wave standard siren measurements reach $1\%$ on $H_0$, as expected, they would significantly improve future CMB+BAO constraints on curvature and on the dark energy equation of state by up to a factor $\sim 3$. We also show that the inclusion of $H_0$ constraints from gravitational-wave standard sirens could result in a reduction of the dark energy figure-of-merit (i.e., the cosmological parameter volume) by up to a factor of $\sim 400$.

astro-ph.CO↗

arXiv2018

Does the Black Hole Merger Rate Evolve with Redshift?

We explore the ability of gravitational-wave detectors to extract the redshift distribution of binary black hole (BBH) mergers. The evolution of the merger rate across redshifts $0 < z \lesssim 1$ is directly tied to the formation and evolutionary processes, providing insight regarding the progenitor formation rate together with the distribution of time delays between formation and merger. Because the limiting distance to which BBHs are detected depends on the masses of the binary, the redshift distribution of detected binaries depends on their underlying mass distribution. We therefore consider the mass and redshift distributions simultaneously, and fit the merger rate density, ${dN}/{dm_1\,dm_2\,dz}$. Our constraints on the mass distribution agree with previously published results, including evidence for an upper mass cutoff at $\sim 40 \ M_\odot$. Additionally, we show that the current set of six BBH detections are consistent with a merger rate density that is uniform in comoving volume. Although our constraints on the redshift distribution are not yet tight enough to distinguish between BBH formation channels, we show that it will be possible to distinguish between different astrophysically motivated models of the merger rate evolution with $\sim 100$--$300$ LIGO-Virgo detections (to be expected within 2--5 years). Specifically, we will be able to infer whether the formation rate peaks at higher or lower redshifts than the star formation rate, or the typical time delay between formation and merger. Meanwhile, with $\sim 100$ detections, the inferred redshift distribution will place constraints on more exotic scenarios such as modified gravity.

astro-ph.HE↗

arXiv2018

Limits on the number of spacetime dimensions from GW170817

The observation of GW170817 in both gravitational and electromagnetic waves provides a number of unique tests of general relativity. One question we can answer with this event is: Do large-wavelength gravitational waves and short-frequency photons experience the same number of spacetime dimensions? In models that include additional non-compact spacetime dimensions, as the gravitational waves propagate, they "leak" into the extra dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and a commensurate systematic error in the inferred distance to the gravitational wave source. Electromagnetic waves would remain unaffected. We compare the inferred distance to GW170817 from the observation of gravitational waves, $d_L^\mathrm{GW}$, with the inferred distance to the electromagnetic counterpart NGC 4993, $d_L^\mathrm{EM}$. We constrain $d_L^\mathrm{GW} = (d_L^\mathrm{EM}/\mathrm{Mpc})^\mathrmγ$ with $γ= 1.01^{+0.04}_{-0.05}$ (for the SHoES value of $H_0$) or $γ= 0.99^{+0.03}_{-0.05}$ (for the Planck value of $H_0$), where all values are MAP and minimal 68% credible intervals. These constraints imply that gravitational waves propagate in $D=3+1$ spacetime dimensions, as expected in general relativity. In particular, we find that $D = 4.02^{+0.07}_{-0.10}$ (SHoES) and $D = 3.98^{+0.07}_{-0.09}$ (Planck). Furthermore, we place limits on the screening scale for theories with $D>4$ spacetime dimensions, finding that the screening scale must be greater than $\sim 20$ Mpc. We also place a lower limit on the lifetime of the graviton of $t > 4.50 \times 10^8$ yr.

gr-qc↗

arXiv2018

A 2 per cent Hubble constant measurement from standard sirens within 5 years

Gravitational wave coalescence events provide an entirely new way to determine the Hubble constant, with the absolute distance calibration provided by the theory of general relativity. This standard siren method was utilized to measure the Hubble constant using LIGO-Virgo's detection of the binary neutron-star merger GW170817, as well as optical identifications of the host galaxy, NGC 4993. The novel and independent measurement is of particular interest given the existing tension between the value of the Hubble constant determined using Type Ia supernovae via the local distance ladder ($73.24 \pm 1.74$) and that from Cosmic Microwave Background observations ($66.93 \pm 0.62$) by $\sim 3$ sigma. Local distance ladder observations may achieve a precision of $1\%$ within 5 years, but at present there are no indications that further observations will substantially reduce the existing discrepancies. In addition to clarifying the discrepancy between existing low and high-redshift measurements, a precision measurement of the Hubble constant is of crucial value in elucidating the nature of the dark energy. Here we show that LIGO and Virgo can be expected to constrain the Hubble constant to a precision of $\sim2\%$ within 5 years and $\sim1\%$ within a decade.

astro-ph.CO↗