Ground-based Laser Interferometers Research Articles

Scattered light monitoring system at the Virgo interferometer: performance improvement and automation based on O3 data

Scattered light, also referred to as scattering, is a nonlinear non stationary noise that can affect data acquired by ground-based laser interferometers for the detection of gravitational waves. A methodology for the identification and daily monitoring of scattering sources, based on the tvf-EMD algorithm, was applied to a large dataset of 132 days of data. Time series of the differential arm motion (DARM) degree of freedom acquired by the Virgo detector during the third LIGO-Virgo scientific run, so called O3, which lasted from 1 April 2019 to 27 March 2020, were considered. The analysis focused on correlation with suspended West end optical bench (SWEB) position data, as SWEB was a known culprit of scattering witnessed in DARM during O3. Different configurations were tested, improving performances with respect to previously obtained results and at the same time making the methodology fully automated. This allows to employ it as a monitoring system both during the phases of detector’s upgrade and in scientific runs such as the fourth scientific run, O4, currently scheduled to start on 2023. The higher values of correlation obtained suggest that tvf-EMD could improve the performance of scattered light noise subtraction from DARM.

Application of Newtonian approximate model to LIGO gravitational wave data processing

With the observation of a series of ground-based laser interferometer gravitational wave (GW) detectors such as LIGO and Virgo, nearly 100 GW events have been detected successively. At present, all detected GW events are generated by the mergers of compact binary systems and are identified through the data processing of matched filtering. Based on matched filtering, we use the GW waveform of the Newtonian approximate (NA) model constructed by linearized theory to match the events detected by LIGO and injections to determine the coalescence time and utilize the frequency curve for data fitting to estimate the parameters of the chirp masses of binary black holes (BBHs). The average chirp mass of our results is , which is very close to provided by GWOSC. In the process, we can analyze LIGO GW events and estimate the chirp masses of the BBHs. This work presents the feasibility and accuracy of the low-order approximate model and data fitting in the application of GW data processing. It is beneficial for further data processing and has certain research value for the preliminary application of GW data.

Stochastic Gravitational-Wave Backgrounds: Current Detection Efforts and Future Prospects

The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction of all GW signals that reach our detectors, while most lie below the confusion limit and are undetected. Similarly to voices in a crowded room, the collection of unresolved signals gives rise to a background that is well-described via stochastic variables and, hence, referred to as the stochastic GW background (SGWB). In this review, we provide an overview of stochastic GW signals and characterise them based on features of interest such as generation processes and observational properties. We then review the current detection strategies for stochastic backgrounds, offering a ready-to-use manual for stochastic GW searches in real data. In the process, we distinguish between interferometric measurements of GWs, either by ground-based or space-based laser interferometers, and timing-residuals analyses with pulsar timing arrays (PTAs). These detection methods have been applied to real data both by large GW collaborations and smaller research groups, and the most recent and instructive results are reported here. We close this review with an outlook on future observations with third generation detectors, space-based interferometers, and potential noninterferometric detection methods proposed in the literature.

On detecting stellar binary black holes via the LISA-Taiji network

The detection of gravitational waves (GWs) by ground-based laser interferometer GW observatories (LIGO/Virgo) reveals a population of stellar binary black holes (sBBHs) with (total) masses up to ∼ 150M ⊙, which are potential sources for space-based GW detectors, such as LISA and Taiji. In this paper, we investigate in details on the possibility of detecting sBBHs by the LISA-Taiji network in future. We adopt the sBBH merger rate density constrained by LIGO/VIRGO observations to randomly generate mock sBBHs samples. Assuming an observation period of 4 years, we find that the LISA-Taiji network may detect several tens (or at least several) sBBHs with signal-to-noise ratio (SNR) > 8 (or > 15), a factor 2 − 3 times larger than that by only using LISA or Taiji observations. Among these sBBHs, no more than a few that can merge during the 4-year observation period. If extending the observation period to 10 years, then the LISA-Taiji network may detect about one hundred (or twenty) sBBHs with SNR> 8 (or > 15), among them about twenty (or at least several) can merge within the observation period. Our results suggest that the LISA-Taiji network may be able to detect at least a handful to twenty or more sBBHs even if assuming a conservative SNR threshold (15) for “detection”, which enables multi-band GW observations by space and ground-based GW detectors. We also further estimate the uncertainties in the parameter estimations of the sBBH systems “detected” by the LISA-Taiji network. We find that the relative errors in the luminosity distance measurements and sky localization are mostly in the range of 0.05 − 0.2 and 1 − 100deg2, respectively, for these sBBHs.

Lensing of gravitational waves as a probe of compact dark matter

ABSTRACT We study gravitational lensing of gravitational waves from compact object binaries as a probe of compact dark matter (DM) objects such as primordial black holes. Assuming a point mass lens, we perform parameter estimation of lensed gravitational wave signals from compact object binaries to determine the detectability of the lens with ground based laser interferometers. Then, considering binary populations that LIGO-Virgo has been probing, we derive a constraint on the abundance of compact DM from non-observation of lensed events. We find that the LIGO-Virgo observations imply that compact objects heavier than $M_l = 200\, {\rm M}_{\odot }$ cannot constitute all DM and less than $40{{\ \rm per\ cent}}$ of DM can be in compact objects heavier than $M_l = 400\, {\rm M}_{\odot }$. We also show that the DM fraction in compact objects can be probed by LIGO in its final sensitivity for $M_l \gt 40\, {\rm M}_{\odot }$ reaching $2{{\ \rm per\ cent}}$ of the DM abundance at $M_l \gt 200\, {\rm M}_{\odot }$, and by ET for $M_l \gt 1\, {\rm M}_{\odot }$ reaching DM fraction as low as 7 × 10−5 at $M_l \gt 40\, {\rm M}_{\odot }$.

Probing dipole radiation from binary neutron stars with ground-based laser-interferometer and atom-interferometer gravitational-wave observatories

Atom-interferometer gravitational-wave (GW) observatory, as a new design of ground-based GW detector for the near future, is sensitive at a relatively low frequency for GW observations. Taking the proposed atom interferometer Zhaoshan Long-baseline Atom Interferometer Gravitation Antenna (ZAIGA), and its illustrative upgrade (Z+) as examples, we investigate how the atom interferometer will complement ground-based laser interferometers in testing the gravitational dipole radiation from binary neutron star (BNS) mergers. A test of such kind is important for a better understanding of the strong equivalence principle laying at the heart of Einstein's general relativity. To obtain a statistically sound result, we sample BNS systems according to their merger rate and population, from which we study the expected bounds on the parameterized dipole radiation parameter $B$. Extracting BNS parameters and the dipole radiation from the combination of ground-based laser interferometers and the atom-interferometer ZAIGA/Z+, we are entitled to obtain tighter bounds on $B$ by a few times to a few orders of magnitude, compared to ground-based laser interferometers alone, ultimately reaching the levels of $|B| \lesssim 10^{-9}$ (with ZAIGA) and $|B| \lesssim 10^{-10}$ (with Z+).

Lensed gravitational waves: Scattering and applications

<p indent="0mm">The direct detection of gravitational waves from stellar-mass compact binary merger by ground-based laser interferometer gravitational wave detector LIGO/Virgo has verified the prediction of general relativity and opened a new chapter in gravitational wave astronomy. Up to now, a total of 50 gravitational wave events have been detected and published in GWTC-1 and GWTC-2 catalogue. In the near future, the third-generation ground based gravitational wave detector, such as the Einstein Telescope (ET), will be constructed with sensitivity improved by at least a factor of 10. Tens of thousands of gravitational wave signals are expected to be detected per year in the third-generation detector era. These gravitational wave signals will inevitably overlap with foreground massive celestial bodies (such as black hole, galaxy and galaxy cluster), thus leading to lensed gravitational wave signals which will undoubtedly be another important test of general relativity once detected. Furthermore, strongly lensed gravitational wave signals by galaxy from massive binary black hole could possibly be detected by future space detector, e.g., LISA and DECIGO. Since the wavelengths of gravitational waves are comparable with the size of some lens, the lensed gravitational waves play a unique role in studying the phenomena of wave nature, e.g., interference and diffraction. Lensed gravitational wave-electromagnetic wave system will have a wide range of applications in fundamental physics, cosmology and astrophysics when a series of lensed gravitational wave events and their corresponding electromagnetic counterparts have been detected. The most obvious advantage of lensed gravitational wave-electromagnetic wave system lies in that gravitational wave could provide time delay information with high accuracy, and electromagnetic wave could provide Fermat potential difference with high precision because a relatively complete arc of light could be obtained by electromagnetic wave observations and this is the most important step in measuring the Fermat potential. Thus, by combining the information from both approaches, lensed gravitational wave-electromagnetic wave system could be applied to study the speed of gravitational waves, constrain cosmological parameters, explore the substructure of the dark matter halo and investigate the lens model and so on. In this paper, we will review in detail how to use geodesic equation, lens equation, as well as wave equation to tackle the stationary scattering problem of lensed gravitational waves, and introduce how lensed gravitational wave-electromagnetic wave system could be applied to study the tensor properties, interference and diffraction effects of gravitational wave, as well as its applications in gravitational wave velocity, Hubble constant, cosmic curvature, lens mass, substructure and so on.

The gravitational-wave landscape

In the fall of 1609, Galileo Galilei opened a window to observe the divine heaven by pointing the telescope skywards. Since then enormous achievements were made in the field of astronomy with dedicated telescopes and satellites, towards a deep understanding of the “electromagnetic universe”. About four hundred years later, the LIGO/Virgo Collaboration discovered, via operating the Michelson interferometers at an unprecedented sensitivity level, a gravitational wave (GW) event, the so-called GW150914, from the merger of a binary black hole. It opened a completely novel window to observe the “gravitational universe”, which is vastly different from the “electromagnetic universe”. The discovery triggered intense researches in the GW field, and many more GW events were observed since then. The summit of the field was delivered by the multimessenger observation of a binary neutron star merger, the so-called GW170817. The event was examined in great detail with joint observations from both GW and electromagnetic instruments. In electromagnetic bands, the counterpart of GW170817 was seen by observations from radio waves, to optical bands, and to X-rays and gamma-rays. The physics revealed by them is extremely rich, and it helped scientists to better understand the equation of state of the supranuclear matters of neutron stars, short gamma-ray bursts, kilonovae, alternative gravity theories, and so on. Despite of many exciting discoveries, the landscape of GWs is much broader than the kilohertz waveband as was already demonstrated. A new era of GWs with extended wavebands is yet to come, with a lot of promising scientific targets. The whole spectrum of GWs will be revealed by: (a) The ground-based laser interferometers that aim for kilohertz GWs, (b) the space-based laser interferometers that aim for millihertz GWs, (c) the pulsar timing arrays that aim for nanohertz GWs, and (d) the specific polarization pattern of cosmic microwave background that was influenced by GWs at the ultra-low frequency at today. To embrace the modern time of GWs, there are still catalogs of puzzles to handle with, in particular, (a) how to build accurate gravitational waveforms that cover a large parameter space with affordable computational costs, (b) how to inversely derive astrophysical information from GWs thus to interpret and learn the physical environments in an unbiased way, (c) how to deal with the increasing complexity of GW time-series data with the help of advanced data-analysis means. These aspects are intrinsically mutually interdependent and the solution of them requests close collaboration of GW scientists from different research sub-fields. A deep understanding of GWs from multiband, as well as multimessenger, aspects is desirable to extract the maximum science output from GW data. Fortunately, both domestically or internationally, great work is being done constantly by groups of researchers and collaboration of them. New patterns among GW scientists are emerging that try to coherently combine relevant knowledge from astronomy, physics, data science, and engineering science. This is crucial for building a big science field, namely, the GW science, to have a great impact on our understanding of the world. These excellent prospects will eventually open up the GW window to our “gravitational universe” thoroughly in the near future, with extremely promising scientific returns.

Improved gravitational radiation time-scales: significance for LISA and LIGO-Virgo sources

ABSTRACT We present a revised version of Peters’ time-scale for the gravitational wave (GW)-induced decay of two point masses. The new formula includes the effects of the first-order post-Newtonian perturbation and additionally provides a simple fit to account for the Newtonian self-consistent evolution of the eccentricity. The revised time-scale is found by multiplying Peters’ estimate by two factors, $R(e_0)= 8^{1-\sqrt{1-e_0}}$ and Qf(p0) = exp (2.5(rS/p0)), where e0 and p0 are the initial eccentricity and periapsis, respectively, and rS the Schwarzschild radius of the system. Their use can correct errors of a factor of 1–10 that arise from using the original Peters’ formula. We apply the revised time-scales to a set of typical sources for existing ground-based laser interferometers and for the future Laser Interferometer Space Antenna (LISA), at the onset of their GW-driven decay. We argue that our more accurate model for the orbital evolution will affect current event- and detection-rate estimates for mergers of compact object binaries, with stronger deviations for eccentric LISA sources, such as extreme and intermediate mass-ratio inspirals. We propose the correction factors R and Qf as a simple prescription to quantify decay time-scales more accurately in future population synthesis models. We also suggest that the corrected time-scale may be used as a computationally efficient alternative to numerical integration in other applications that include the modelling of radiation reaction for eccentric sources.

Detecting gravitational wave bursts with LISA in the presence of instrumental glitches

The Laser Interferometer Space Antenna (LISA) will open a rich discovery space in the milli-Hertz gravitational wave band. In addition to the anticipated signals from many millions of binary systems, this band may contain new and previously un-imagined sources for which we currently have no models. To detect unmodeled and unexpected signals we need to be able to separate them from instrumental noise artifacts, or glitches. Glitches are a regular feature in the data from ground based laser interferometers, and they were also seen in data from the LISA Pathfinder mission. In contrast to the situation on ground, we will not have the luxury of having multiple independent detectors to help separate unmodeled signals from glitches, and new techniques have to be developed. Here we show that unmodeled gravitational wave bursts can be detected with LISA by leveraging the different way in which instrument glitches and gravitational wave bursts imprint themselves in the time-delay interferometery data channels. We show that for signals with periods longer than the light travel time between the spacecraft, the "breathing mode" or Sagnac data combination is key to detection. Conversely, for short period signals it is the time of arrival at each spacecraft that aids separation. We investigate the conditions under which we can distinguish the origin of signals and glitches consisting of a single sine-Gaussian wavelet and determine how well we can characterize the signal. We find that gravitational waves bursts can be unambiguously detected and characterized with just a single data channel (four functioning laser links), though the signal separation and parameter estimation improve significantly when all six laser links are operational.

Gravitational Waves and Gravitational-wave Sourcestwo

The recent discovery of gravitational-wave burst GW150914 marks the coming of a new era of gravitational-wave astronomy, which provides a new window to study the physics of strong gravitational field, extremely massive stars, extremely high energy processes, and extremely early universe. In this article, we introduce the basic characters of gravitational waves in the Einstein's general relativity, their observational effects and main generation mechanisms, including the rotation of neutron stars, evolution of binary systems, and spontaneous generation in the inflation universe. Different sources produce the gravitational waves at quite different frequencies, which can be detected by different methods. In the lowest frequency range (f<10−15Hz), the detection is mainly dependent of the observation of B-mode polarization of cosmic microwave background radiation. In the middle frequency range (10−9<f<10−6Hz), the gravitational waves are detected by analyzing the timing residuals of millisecond pulsars. And in the high frequency range (10−4<f<104Hz), they can be detected by the space-based and ground-based laser interferometers. In particular, we focus on the main features, detection methods, detection status, and the future prospects for several important sources, including the continuous sources (e.g., the spinning neutron stars, and stable binary systems), the burst sources (e.g., the supernovae, and the merge of binary system), and the stochastic backgrounds generated by the astrophysical and cosmological process. In addition, we forecast the potential breakthroughs in gravitational-wave astronomy in the near future, and the Chinese projects which might involve in these discoveries.

The Gravitational Wave Signal from Core-collapse Supernovae

Abstract We study gravitational waves (GWs) from a set of 2D multigroup neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Our goal is to systematize the current knowledge about the post-bounce CCSN GW signal and recognize the templatable features that could be used by the ground-based laser interferometers. We demonstrate that, starting from ∼400 ms after core bounce, the dominant GW signal represents the fundamental quadrupole (l = 2) oscillation mode (f-mode) of the proto–neutron star (PNS), which can be accurately reproduced by a linear perturbation analysis of the angle-averaged PNS profile. Before that, in the time interval between ∼200 and ∼400 ms after bounce, the dominant mode has two radial nodes and represents a g-mode. We associate the high-frequency noise in the GW spectrograms above the main signal with p-modes, while below the dominant frequency there is a region with very little power. The collection of models presented here summarizes the dependence of the CCSN GW signal on the progenitor mass, equation of state, many-body corrections to the neutrino opacity, and rotation. Weak dependence of the dominant GW frequency on the progenitor mass motivates us to provide a simple fit for it as a function of time, which can be used as a prior when looking for CCSN candidates in the LIGO data.

Constraining Alternative Theories of Gravity Using Pulsar Timing Arrays.

The opening of the gravitational wave window by ground-based laser interferometers has made possible many new tests of gravity, including the first constraints on polarization. It is hoped that, within the next decade, pulsar timing will extend the window by making the first detections in the nanohertz frequency regime. Pulsar timing offers several advantages over ground-based interferometers for constraining the polarization of gravitational waves due to the many projections of the polarization pattern provided by the different lines of sight to the pulsars, and the enhanced response to longitudinal polarizations. Here, we show that existing results from pulsar timing arrays can be used to place stringent limits on the energy density of longitudinal stochastic gravitational waves. However, unambiguously distinguishing these modes from noise will be very difficult due to the large variances in the pulsar-pulsar correlation patterns. Existing upper limits on the power spectrum of pulsar timing residuals imply that the amplitude of vector longitudinal (VL) and scalar longitudinal (SL) modes at frequencies of 1/year are constrained, A_{VL}<4×10^{-16} and A_{SL}<4×10^{-17}, while the bounds on the energy density for a scale invariant cosmological background are Ω_{VL}h^{2}<4×10^{-11} and Ω_{SL}h^{2}<3×10^{-13}.

DISTINGUISHING COMPACT BINARY POPULATION SYNTHESIS MODELS USING GRAVITATIONAL WAVE OBSERVATIONS OF COALESCING BINARY BLACK HOLES

The coalescence of compact binaries containing neutron stars or black holes is one of the most promising signals for advanced ground-based laser interferometer gravitational-wave detectors, with the first direct detections expected over the next few years. The rate of binary coalescences and the distribution of component masses is highly uncertain, and population synthesis models predict a wide range of plausible values. Poorly constrained parameters in population synthesis models correspond to poorly understood astrophysics at various stages in the evolution of massive binary stars, the progenitors of binary neutron star and binary black hole systems. These include effects such as supernova kick velocities, parameters governing the energetics of common envelope evolution and the strength of stellar winds. Observing multiple binary black hole systems through gravitational waves will allow us to infer details of the astrophysical mechanisms that lead to their formation. Here we simulate gravitational-wave observations from a series of population synthesis models including the effects of known selection biases, measurement errors and cosmology. We compare the predictions arising from different models and show that we will be able to distinguish between them with observations (or the lack of them) from the early runs of the advanced LIGO and Virgo detectors. This will allow us to narrow down the large parameter space for binary evolution models.

Phase-coherent mapping of gravitational-wave backgrounds using ground-based laser interferometers

We extend the formalisms developed in Gair et al. and Cornish and van Haasteren to create maps of gravitational-wave backgrounds using a network of ground-based laser interferometers. We show that in contrast to pulsar timing arrays, which are insensitive to half of the gravitational-wave sky (the curl modes), a network of ground-based interferometers is sensitive to both the gradient and curl components of the background. The spatial separation of a network of interferometers, or of a single interferometer at different times during its rotational and orbital motion around the Sun, allows for recovery of both components. We derive expressions for the response functions of a laser interferometer in the small-antenna limit, and use these expressions to calculate the overlap reduction function for a pair of interferometers. We also construct maximum-likelihood estimates of the + and x-polarization modes of the gravitational-wave sky in terms of the response matrix for a network of ground-based interferometers, evaluated at discrete times during Earth's rotational and orbital motion around the Sun. We demonstrate the feasibility of this approach for some simple simulated backgrounds (a single point source and spatially-extended distributions having only grad or curl components), calculating maximum-likelihood sky maps and uncertainty maps based on the (pseudo)inverse of the response matrix. The distinction between this approach and standard methods for mapping gravitational-wave power is also discussed.

Status of advanced ground-based laser interferometers for gravitational-wave detection

Ground-based laser interferometers for gravitational-wave (GW) detection were first constructed starting 20 years ago and as of 2010 collection of several years’ worth of science data at initial design sensitivities was completed. Upgrades to the initial detectors together with construction of brand new detectors are ongoing and feature advanced technologies to improve the sensitivity to GWs. This conference proceeding provides an overview of the common design features of ground-based laser interferometric GW detectors and establishes the context for the status updates of each of the four gravitational-wave detectors around the world: Advanced LIGO, Advanced Virgo, GEO 600 and KAGRA.

Detectability of bigravity with graviton oscillations using gravitational wave observations

The gravitational waveforms in the ghost-free bigravity theory exhibit deviations from those in general relativity. The main difference is caused by graviton oscillations in the bigravity theory. We investigate the prospects for the detection of the corrections to gravitational waveforms from coalescing compact binaries due to graviton oscillations and for constraining bigravity parameters with the gravitational wave observations. We consider the bigravity model discussed by the De Felice-Nakamura-Tanaka subset of the bigravity model, and the phenomenological model in which the bigravity parameters are treated as independent variables. In both models, the bigravity waveform shows strong amplitude modulation, and there can be a characteristic frequency of the largest peak of the amplitude, which depends on the bigravity parameters. We show that there is a detectable region of the bigravity parameters for the advanced ground-based laser interferometers, such as Advanced LIGO, Advanced Virgo, and KAGRA. This region corresponds to the effective graviton mass of $\ensuremath{\mu}\ensuremath{\gtrsim}{10}^{\ensuremath{-}17}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ for $\stackrel{\texttildelow{}}{c}\ensuremath{-}1\ensuremath{\gtrsim}{10}^{\ensuremath{-}19}$ in the phenomenological model, while $\ensuremath{\mu}\ensuremath{\gtrsim}{10}^{\ensuremath{-}16.5}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ for $\ensuremath{\kappa}{\ensuremath{\xi}}_{c}^{2}\ensuremath{\gtrsim}{10}^{0.5}$ in the De Felice-Nakamura-Tanaka subset of the bigravity model, respectively, where $\stackrel{\texttildelow{}}{c}$ is the propagation speed of the massive graviton and $\ensuremath{\kappa}{\ensuremath{\xi}}_{c}^{2}$ corresponds to the corrections to the gravitational constant in general relativity. These regions are not excluded by existing solar system tests. We also show that, in the case of $1.4\ensuremath{-}1.4{M}_{\ensuremath{\bigodot}}$ binaries at the distance of 200 Mpc, $\mathrm{log}{\ensuremath{\mu}}^{2}$ is determined with an accuracy of $\mathcal{O}(0.1)%$ at the $1\ensuremath{\sigma}$ level for a fiducial model with ${\ensuremath{\mu}}^{2}=1{0}^{\ensuremath{-}33}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$ in the case of the phenomenological model.

Measuring the Hubble constant using gravitational waves

Second-generation ground-based laser interferometers are expected to deliver a wealth of gravitational waves (GW) events from coalescing compact binaries up to a redshift of about 0.3. Being free of the systematics affecting electromagnetic measurements, GW offer the possibility of an independent measurement of H0. This paper presents a method based on Bayesian inference aimed at estimating the value of the cosmological parameters for any GW event. In contrast to earlier work, this framework does not require the precise identification of the putative optical counterpart, but it considers all the potential galaxy hosts consistent with the recovered sky position and distance posterior distributions. When applied to the upcoming network of second generation interferometers, 50 GW events will yield a measurement of H0 with an uncertainty of a few per cents.

BLACK HOLE TRIPLE DYNAMICS: A BREAKDOWN OF THE ORBIT AVERAGE APPROXIMATION AND IMPLICATIONS FOR GRAVITATIONAL WAVE DETECTIONS

Coalescing black hole (BH) binaries forming in the dense core of globular clusters (GCs) are expected to be one the brightest sources of gravitational wave (GW) radiation for the next generation of ground-based laser interferometers. Favorable conditions for merger are initiated by the Kozai resonance in which the gravitational interaction with a third distant object, typically another BH, induces quasi-periodic variations of the inner BH binary eccentricity. In this paper we perform high precision N-body simulations of the long term evolution of hierarchical BH triples and investigate the conditions that lead to the merging of the BH binary and the way it might become an observable source of GW radiation. We find that the secular orbit average treatment, adopted in previous works, does not reliably describe the dynamics of these systems if the binary is orbited by the outer BH on a highly inclined orbit at a moderate distance. During the high eccentricity phase of a Kozai cycle the torque due to the outer BH can drive the binary to extremely large eccentricities in a fraction of the binary's orbital period. This occurs before relativistic terms become important to the evolution and allows the binary GW signal to reach large GW frequencies (>~10 Hz) at high eccentricities. We show that ~50 % of coalescing BH binaries driven by the Kozai mechanism in GCs will have eccentricities larger than 0.1, with 10 % of them being extremely eccentric, (1-e)<~10^-5, when they first chirp in the frequency band of ground based laser interferometers. This implies that a large fraction of such GW sources could be missed if conventional quasi-circular templates are used for analysis of GW detectors data. The efficient detection of all coalescing BH binaries in GCs will therefore require template banks of eccentric inspiral waveforms for matched-filtering and dedicated search strategies.

Interdependent perturbations of the Earth’s surface, atmosphere, and ionosphere

The results of original experiments performed with a ground-based geophysical laser interferometer and a GPS-based satellite ionospheric profilometer are given. Synchronous growth was recorded for deformations of the Earth’s surface and variations in the atmospheric pressure and in the level of spatiotemporal modifications of the electron content within the ionospheric F2 layer with characteristic space scales of 102–103 km and periods of 102–103 s. The relationship between the revealed phenomena and the Earth’s seismic activity is analyzed.