First Gravitational Wave Research Articles

GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs

We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1$\mathrm{M}_\odot$ during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September $12^\mathrm{th}$, 2015 to January $19^\mathrm{th}$, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November $30^\mathrm{th}$, 2016 to August $25^\mathrm{th}$, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818 and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between $18.6_{-0.7}^{+3.2}\mathrm{M}_\odot$, and $84.4_{-11.1}^{+15.8} \mathrm{M}_\odot$, and range in distance between $320_{-110}^{+120}$ Mpc and $2840_{-1360}^{+1400}$ Mpc. No neutron star - black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of $110\, -\, 3840$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$ for binary neutron stars and $9.7\, -\, 101$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$ for binary black holes assuming fixed population distributions, and determine a neutron star - black hole merger rate 90% upper limit of $610$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$.

Confronting gravitational-wave observations with modern nuclear physics constraints

Multi-messenger observations of neutron star (NS) mergers have the potential to revolutionize nuclear astrophysics. They will improve our understanding of nucleosynthesis, provide insights about the equation of state (EOS) of strongly-interacting matter at high densities, and enable tests of the theory of gravity and of dark matter. Here, we focus on the EOS, where both gravitational waves (GWs) from neutron-star mergers and X-ray observations from space-based detectors such as NICER will provide more stringent constraints on the structure of neutron stars. Furthermore, recent advances in nuclear theory have enabled reliable calculations of the EOS at low densities using effective field theory based Hamiltonians and advanced techniques to solve the quantum many-body problem. In this paper, we address how the first observation of GWs from GW170817 can be combined with modern calculations of the EOS to extract useful insights about the EOS of matter encountered inside neutron stars. We analyze the impact of various uncertainties, the role of phase transitions in the NS core, and discuss how future observations will improve our understanding of dense matter.

Constraining the relativistic mean-field model equations of state with gravitational wave observations

The first detection of gravitational waves from the binary neutron star merger event GW170817 has started to provide important new constraints on the nuclear equation of state at high density. The tidal deformability bound of GW170817 combined with the observed two solar mass neutron star poses a serious challenge to theoretical formulations of realistic equations of state. We analyze a fully comprehensive set of relativistic nuclear mean-field theories by confronting them with the observational bounds and the measured neutron-skin thickness. We find that only a few models can withstand these bounds which predict a stiff overall equation of state but with a soft neutron-proton symmetry energy. Two possible indications are proposed: Circumstantial evidence of hadron-quark phase transition inside the star and new parametrizations that are consistent with ground state properties of finite nuclei and observational bounds. Based on extensive analysis of these sets, an upper limit on the radius of a $1.4M_\odot$ neutron star of $R_{1.4}\lesssim 12.9$ km is deduced.

Constraints on the neutron star equation of state from GW170817

The first detection of gravitational waves from a neutron star-neutron star merger, GW170817, has opened up a new avenue for constraining the ultradense-matter equation of state (EOS). The deviation of the observed waveform from a point-particle waveform is a sensitive probe of the EOS controlling the merging neutron stars' structure. In this topical review, I discuss the various constraints that have been made on the EOS in the year following the discovery of GW170817. In particular, I review the surprising relationship that has emerged between the effective tidal deformability of the binary system and the neutron star radius. I also report new results that make use of this relationship, finding that the radius inferred from GW170817 lies between 9.8 and 13.2 km at 90% confidence, with distinct likelihood peaks at 10.8 and 12.3 km. I compare these radii, as well as those inferred in the literature, to X-ray measurements of the neutron star radius. I also summarize the various maximum mass constraints, which point towards a maximum mass < 2.3 M_sun, depending on the fate of the remnant, and which can be used to additionally constrain the high-density EOS. I review the constraints on the EOS that have been performed directly, through Bayesian inference schemes. Finally, I comment on the importance of disentangling thermal effects in future EOS constraints from neutron star mergers.

Listening to the songs of the universe: How vibration control for the laser interferometer gravitational-wave observatory (LIGO) allows us to measure ripples in the fabric of space

In 2015, humanity made the first detection of gravitational waves from the violent collision of two black holes. As Einstein predicted, this collision sent waves through the fabric of space-time, but nearly 100 years passed between Einstein's prediction and the first measurement of these waves by the advanced LIGO detectors. The detection was made possible by many advances in the precision measurement. I will describe the detectors and one of the key technologies, the vibration isolation for the optics; at 10 Hz, the motion of the LIGO mirrors is at least 1,000,000,000 times less than the motion of the ground. By creating one of the quietest places on Earth, we have created a new way to listen to the stars.In 2015, humanity made the first detection of gravitational waves from the violent collision of two black holes. As Einstein predicted, this collision sent waves through the fabric of space-time, but nearly 100 years passed between Einstein's prediction and the first measurement of these waves by the advanced LIGO detectors. The detection was made possible by many advances in the precision measurement. I will describe the detectors and one of the key technologies, the vibration isolation for the optics; at 10 Hz, the motion of the LIGO mirrors is at least 1,000,000,000 times less than the motion of the ground. By creating one of the quietest places on Earth, we have created a new way to listen to the stars.

LIGO and Gravitational Waves, III: Nobel Lecture, December 8, 2017

The first observation of gravitational waves, by LIGO on September 14, 2015, was the culmination of a near half century effort by ∼1200 scientists and engineers of the LIGO/Virgo Collaboration. It was also the remarkable beginning of a whole new way to observe the universe: gravitational astronomy. The Nobel Prize for “decisive contributions” to this triumph was awarded to only three members of the Collaboration: Rainer Weiss, Barry Barish, and me. But, in fact, it is the entire collaboration that deserves the primary credit. For this reason, in accepting the Nobel Prize, I regard myself as an icon for the Collaboration.

A telescope for LISA – the Laser Interferometer Space Antenna

Abstract Gravitational waves are a prediction of Einstein’s general relativity theory. In autumn 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO; https://www.ligo.caltech.edu/) experiment reported the first detection of gravitational waves in addition to electromagnetic radiation from the collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light and opens the door to a new type of astronomical observatory based on gravitational waves. The gravitational wave spectrum covers a broad span of frequencies and requires both space- and ground-based observatories to cover the full range. Space-based gravitational wave observatories, such as the proposed Laser Interferometer Space Antenna (LISA), operate at frequencies between 0.1 mHz and 1 Hz and complement the frequency range of 30–1000 Hz accessible by ground-based gravitational wave observatories, such as LIGO. A rich array of high-energy astrophysical sources is expected in the LISA measurement band. LISA was selected in 2017 as the third large mission of the Cosmic Vision program of the European Space Agency. The National Aeronautics and Space Administration will collaborate on both the scientific and technical aspects of this mission. This paper addresses the design of the optical telescope as an essential component of LISA’s long-distance interferometric measurement system.

Sensing and Vetoing Loud Transient Noises for the Gravitational-wave Detection

Since the first detection of gravitational-wave (GW), GW150914, September 14th 2015, the multi-messenger astronomy added a new way of observing the Universe together with electromagnetic (EM) waves and neutrinos. After two years, GW together with its EM counterpart from binary neutron stars, GW170817 and GRB170817A, has been observed. The detection of GWs opened a new window of astronomy/astrophysics and will be an important messenger to understand the Universe. In this article, we briefly review the gravitational-wave and the astrophysical sources and introduce the basic principle of the laser interferometer as a gravitational-wave detector and its noise sources to understand how the gravitational-waves are detected in the laser interferometer. Finally, we summarize the search algorithms currently used in the gravitational-wave observatories and the detector characterization algorithms used to suppress noises and to monitor data quality in order to improve the reach of the astrophysical searches.

Local merger rates of double neutron stars

AbstractThe first detection of gravitational waves from a merging double neutron star (DNS) binary implies a much higher rate of DNS coalescences in the local Universe than typically estimated on theoretical grounds. The recent study by Chruslinska et al. (2018) shows that apart from being particularly sensitive to the common envelope treatment, DNS merger rates appear rather robust against variations of several factors probed in their study (e.g. conservativeness of the mass transfer, angular momentum loss, and natal kicks), unless extreme assumptions are made. Confrontation with the improving observational limits may allow to rule out some of the extreme models. To correctly compare model predictions with observational limits one has to account for the other factors that affect the rates. One of those factors relates to the assumed history of star formation and chemical evolution of the Universe and its impact on the final results needs to be better constrained.

Presupernova Evolution and Explosive Nucleosynthesis of Rotating Massive Stars in the Metallicity Range −3 ≤ [Fe/H] ≤ 0

Abstract We present a new grid of presupernova models of massive stars extending in mass between 13 and 120 , covering four metallicities (i.e., [Fe/H] = 0, −1, −2, and −3) and three initial rotation velocities (i.e., 0, 150, and 300 km s−1). The explosion has been simulated following three different assumptions in order to show how the yields depend on the remnant mass−initial mass relation. An extended network from H to Bi is fully coupled to the physical evolution of the models. The main results can be summarized as follows. (a) At solar metallicity, the maximum mass exploding as a red supergiant (RSG) is of the order of 17 in the nonrotating case, with the more massive stars exploding as Wolf–Rayet (WR) stars. All rotating models, conversely, explode as WR stars. (b) The interplay between the core He-burning and the H-burning shell, triggered by the rotation-induced instabilities, drives the synthesis of a large primary amount of all the products of CNO, not just . A fraction of them greatly enriches the radiative part of the He core (and is responsible for the large production of F), and a fraction enters the convective core, leading therefore to an important primary neutron flux able to synthesize heavy nuclei up to Pb. (c) In our scenario, remnant masses of the order of those inferred from the first detections of gravitational waves (GW 150914, GW 151226, GW 170104, GW 170814) are predicted at all metallicities for none or moderate initial rotation velocities.

The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

We discuss the different signals, in gravitational and electromagnetic waves, emitted during the merger of two compact stars. We will focus in particular on the possible contraints that those signals can provide on the equation of state of dense matter. Indeed, the stiffness of the equation of state and the particle composition of the merging compact stars strongly affect, e.g., the life time of the post-merger remnant and its gravitational wave signal, the emission of the short gamma-ray-burst, the amount of ejected mass and the related kilonova. The first detection of gravitational waves from the merger of two compact stars in August 2017, GW170817, and the subsequent detections of its electromagnetic counterparts, GRB170817A and AT2017gfo, is the first example of the era of “multi-messenger astronomy”: we discuss what we have learned from this detection on the equation of state of compact stars and we provide a tentative interpretation of this event, within the two families scenario, as being due to the merger of a hadronic star with a quark star.

GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences.

The LIGO Scientific and Virgo Collaborations have announced the event GW170817, the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star component will add to the contribution from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25Hz), we predict a total astrophysical background with amplitude Ω_{GW}(f=25 Hz)=1.8_{-1.3}^{+2.7}×10^{-9} with 90%confidence, compared with Ω_{GW}(f=25 Hz)=1.1_{-0.7}^{+1.2}×10^{-9} from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.

Imaging Correlations in Heterodyne Spectra for Quantum Displacement Sensing.

The extraordinary sensitivity of the output field of an optical cavity to small quantum-scale displacements has led to breakthroughs such as the first detection of gravitational waves and of the motions of quantum ground-state cooled mechanical oscillators. While heterodyne detection of the output optical field of an optomechanical system exhibits asymmetries which provide a key signature that the mechanical oscillator has attained the quantum regime, important quantum correlations are lost. In turn, homodyning can detect quantum squeezing in an optical quadrature but loses the important sideband asymmetries. Here we introduce and experimentally demonstrate a new technique, subjecting the autocorrelators of the output current to filter functions, which restores the lost heterodyne correlations (whether classical or quantum), drastically augmenting the useful information accessible. The filtering even adjusts for moderate errors in the locking phase of the local oscillator. Hence we demonstrate the single-shot measurement of hundreds of different field quadratures allowing the rapid imaging of detailed features from a simple heterodyne trace. We also obtain a spectrum of hybrid homodyne-heterodyne character, with motional sidebands of combined amplitudes comparable to homodyne. Although investigated here in a thermal regime, the method's robustness and generality represents a promising new approach to sensing of quantum-scale displacements.

Status of Advanced Virgo

The LIGO and the Virgo collaborations have recently announced the first detections of Gravitational Waves. Due to their weak amplitude, Gravitational Waves are expected to produce a very small effect on free-falling masses, which undergo a displacement of the order of 10-18 m for a Km-scale mutual distance. This discovery showed that interferometric detectors are suitable to reveal such a feeble effect, and therefore represent a new tool for astronomy, astrophysics and cosmology in the understanding of the Universe. To better reconstruct the position of the Gravitational Wave source and increase the signal-to-noise ratio of the events by means of multiple coincidence, a network of detectors is necessary. In the USA, the LIGO project has recently concluded its second Observation Run (O2) with a couple of twin 4 kilometer-long arms detectors which are placed in Washington State and Louisiana. Advanced VIRGO (AdV) is a 3 kilometer-long arms second generation interferometer situated in Cascina, near Pisa in Italy. The installation of AdV has been completed in 2016, and the first commissioning phase allowed to get to the target early-stage sensitivity, which was sufficient to join LIGO in the O2 scientific run. In this paper, the challenges of the commissioning of AdV will be presented, together with its current performances and future perspectives. Finally, in the last paragraph the latest discoveries that occurred after the ICNFP 2017 conference will be also described.

A new cosmic messenger

The first observation of gravitational waves from two merging neutron stars that was recently made by the LIGO and Virgo detectors has – along with date from telescopes across the globe and in space – kicked off a new era in multimessenger astronomy. Imre Bartos describes this watershed moment, which crowned decades of research and will shape the future of observational astronomy

A More Stringent Constraint on the Mass Ratio of Binary Neutron Star Merger GW170817

Abstract Recently, the LIGO–Virgo Collaborations reported their first detection of gravitational-wave (GW) signals from the low-mass compact binary merger GW170817, which is most likely due to a double neutron star (NS) merger. With the GW signals only, the chirp mass of the binary is precisely constrained to , but the mass ratio is loosely constrained in the range 0.4–1, so that a very rough estimation of the individual NS masses (1.36 M ⊙ &lt; M 1 &lt; 2.26 M ⊙ and 0.86 M ⊙ &lt; M 2 &lt; 1.36 M ⊙) was obtained. Here, we propose that if one can constrain the dynamical ejecta mass through performing kilonova modeling of the optical/IR data, by utilizing an empirical relation between the dynamical ejecta mass and the mass ratio of NS binaries, one may place a more stringent constraint on the mass ratio of the system. For instance, considering that the red “kilonova” component is powered by the dynamical ejecta, we reach a tight constraint on the mass ratio in the range of 0.46–0.59. Alternatively, if the blue “kilonova” component is powered by the dynamical ejecta, the mass ratio would be constrained in the range of 0.53–0.67. Overall, such a multi-messenger approach could narrow down the mass ratio of GW170817 system to the range of 0.46–0.67, which gives a more precise estimation of the individual NS mass than pure GW signal analysis, i.e., 1.61 M ⊙ &lt; M 1 &lt; 2.11 M ⊙ and 0.90 M ⊙ &lt; M 2 &lt; 1.16 M ⊙.

A technical overview of the LIGO detectors

The LIGO detectors are a technological marvel, the culmination of ~50 years of research and development, that have opened up a new window on the universe by making the first detections of gravitational waves. The LIGO detectors can measure strain caused by gravitational wave perturbations down to 10-23 (at their most sensitive frequency band). In this talk, I will give an overview of the techniques that have allowed us to reach such incredible precision, and where possible relate said techniques to the field of acoustics.

The detection of gravitational waves

On February 11 2016 the scientific community was surprised by the announcement of the first observation of gravitational waves made by the LIGO and Virgo collaborations. The signal was named GW150914 indicating that the astrophysical event that produced it occurred the 14 of September of 2015. The detected waveform is consistent with the predictions of general relativity for the spiral and merger of a binary black hole system and subsequent relaxation period known as ring down of the resulting black hole. That detection was the first direct evidence of the existence of gravitational waves and the first observation of the merger of a binary black hole system1.

The First Detection of Gravitational Waves

This article deals with the first detection of gravitational waves by the advanced Laser Interferometer Gravitational Wave Observatory (LIGO) detectors on 14 September 2015, where the signal was generated by two stellar mass black holes with masses 36 M ⊙ and 29 M ⊙ that merged to form a 62 M ⊙ black hole, releasing 3 M ⊙ energy in gravitational waves, almost 1.3 billion years ago. We begin by providing a brief overview of gravitational waves, their sources and the gravitational wave detectors. We then describe in detail the first detection of gravitational waves from a binary black hole merger. We then comment on the electromagnetic follow up of the detection event with various telescopes. Finally, we conclude with the discussion on the tests of gravity and fundamental physics with the first gravitational wave detection event.

A Surrogate model of gravitational waveforms from numerical relativity simulations of precessing binary black hole mergers

We present the first surrogate model for gravitational waveforms from the coalescence of precessing binary black holes. We call this surrogate model NRSur4d2s. Our methodology significantly extends recently introduced reduced-order and surrogate modeling techniques, and is capable of directly modeling numerical relativity waveforms without introducing phenomenological assumptions or approximations to general relativity. Motivated by GW150914, LIGO's first detection of gravitational waves from merging black holes, the model is built from a set of $276$ numerical relativity (NR) simulations with mass ratios $q \leq 2$, dimensionless spin magnitudes up to $0.8$, and the restriction that the initial spin of the smaller black hole lies along the axis of orbital angular momentum. It produces waveforms which begin $\sim 30$ gravitational wave cycles before merger and continue through ringdown, and which contain the effects of precession as well as all $\ell \in \{2, 3\}$ spin-weighted spherical-harmonic modes. We perform cross-validation studies to compare the model to NR waveforms \emph{not} used to build the model, and find a better agreement within the parameter range of the model than other, state-of-the-art precessing waveform models, with typical mismatches of $10^{-3}$. We also construct a frequency domain surrogate model (called NRSur4d2s_FDROM) which can be evaluated in $50\, \mathrm{ms}$ and is suitable for performing parameter estimation studies on gravitational wave detections similar to GW150914.