Academic literature on the topic 'Echoes, binary black hole, data analysis, general relativity'

The conformal method for constructing initial data for Einstein's equations is presented in both the Hamiltonian and Lagrangian picture (extrinsic curvature decomposition and conformal thin sandwich formalism, respectively), and advantages due to the recent introduction of a weight-function in the extrinsic curvature decomposition are discussed. I then describe recent progress in numerical techniques to solve the resulting elliptic equations, and explore innovative approaches toward the construction of astrophysically realistic initial data for binary black hole simulations.

Ringdown gravitational waves of compact object binaries observed by ground-based gravitational-wave detectors encapsulate rich information to understand remnant objects after the merger and to test general relativity in the strong field. In this work, we investigate the ringdown gravitational waves in detail to better understand their property, assuming that the remnant objects are black holes. For this purpose, we perform numerical simulations of post-merger phase of binary black holes by using the black hole perturbation scheme with the initial data given under the close-limit approximation, and we generate data of ringdown gravitational waves with smaller numerical errors than that associated with currently available numerical relativity simulations. Based on the analysis of the data, we propose an orthonormalization of the quasinormal mode functions describing the fundamental tone and overtones to model ringdown gravitational waves. Finally, through some demonstrations of the proposed model, we briefly discuss the prospects for ringdown gravitational-wave data analysis including the overtones of quasinormal modes.

To evaluate a potential usually one analyzes trajectories of test particles. For the Galactic Center case astronomers use bright stars or photons, so there are two basic observational techniques to investigate a gravitational potential, namely, (a) monitoring the orbits of bright stars near the Galactic Center as it is going on with 10m Keck twin and four 8m VLT telescopes equipped with adaptive optics facilities (in addition, recently the IR interferometer GRAVITY started to operate with VLT); (b) measuring the size and shape of shadows around black hole with VLBI-technique using telescopes operating in mm-band. At the moment, one can use a small relativistic correction approach for stellar orbit analysis, however, in the future the approximation will not be precise enough due to enormous progress of observational facilities and recently the GRAVITY team found that the first post-Newtonian correction has to be taken into account for the gravitational redshift in the S2 star orbit case. Meanwhile for smallest structure analysis in VLBI observations one really needs a strong gravitational field approximation. We discuss results of observations and their interpretations. In spite of great efforts there is a very slow progress to resolve dark matter (DM) and dark energy (DE) puzzles and in these circumstances in last years a number of alternative theories of gravity have been proposed. Parameters of these theories could be effectively constrained with of observations of the Galactic Center. We show some cases of alternative theories of gravity where their parameters are constrained with observations, in particular, we consider massive theory of gravity. We choose the alternative theory of gravity since there is a significant activity in this field and in the last years theorists demonstrated an opportunity to create such theories without ghosts, on the other hand, recently, the joint LIGO & Virgo team presented an upper limit on graviton mass such as mg< 1:2 × 10-22eV [1] analyzing gravitational wave signal in their first paper where they reported about the discovery of gravitational waves from binary black holes as it was suggested by C. Will [2]. So, the authors concluded that their observational data do not indicate a significant deviation from classical general relativity. We show that an analysis of bright star trajectories could estimate a graviton mass with a commensurable accuracy in comparison with an approach used in gravitational wave observations and the estimates obtained with these two approaches are consistent. Therefore, such an analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a useful tool to obtain constraints on the fundamental gravity law. We showed that in the future graviton mass estimates obtained with analysis of trajectories of bright stars would be better than current LIGO bounds on the value, therefore, based on a potential reconstruction at the Galactic Center we obtain bounds on a graviton mass and these bounds are comparable with LIGO constraints. Analyzing size of shadows around the supermassive black hole at the Galactic Center (or/and in the center of M87) one could constrain parameters of different alternative theories of gravity as well.

We search for gravitational waves from the coalescence (inspiral, merger and ringdown) of binary black holes with data from the Laser Interferometer Gravitational-Wave Observatory (LIGO). Provided with well-described waveform models from General Relativity, matched filtering is employed in the GSTLAL analysis pipeline as the optimal detection technique for weak signals in Gaussian noise. The GSTLAL analysis pipeline filters data with waveform template banks, identifies triggers with SNR greater than 4, forms coincident triggers between multiple detectors in the LSC-Virgo Collaboration, and attempts to optimally separate signal from detector background noise fluctuations using a Chisquared test. We analyze high-statistics simulations of binary merger waveforms injected into LIGO recolored S6 data to evaluate the pipeline search sensitivity and to test the readiness of the pipeline for Advanced LIGO. With Advanced LIGO fully in operation by 2015 and the upgraded analysis pipelines, the expected detection rate is increased to as much as 100 events/year or more as compared to 0.01–1 events/year in Initial LIGO. Our work will make it possible to detect gravitational waves from binary black hole coalescence in Advanced LIGO data with high confidence. KEYWORDS: LIGO, Gravitational Waves, General Relativity, Coalescence, Black Hole Binaries, Noise Fluctuations, Matched Filtering, Chi-squared Test, Simulations, GSTLAL Analysis Pipeline

Abstract Interferometric gravitational-wave observatories have opened a new era in astronomy. The rich data produced by an international network enables detailed analysis of the curved space-time around black holes. With nearly one hundred signals observed so far and thousands expected in the next decade, their population properties enable insights into stellar evolution and the expansion of our Universe. However, the detectors are afflicted by transient noise artefacts known as ‘glitches’ which contaminate the signals and bias inferences. Of the 90 signals detected to date, 18 were contaminated by glitches. This feasibility study explores a new approach to transient gravitational-wave data analysis using Gaussian processes, which model the underlying physics of the glitch-generating mechanism rather than the explicit realisation of the glitch itself. We demonstrate that if the Gaussian process kernel function can adequately model the glitch morphology, we can recover the parameters of simulated signals. Moreover, we find that the Gaussian processes kernels used in this work are well-suited to modelling long-duration glitches which are most challenging for existing glitch-mitigation approaches. Finally, we show how the time-domain nature of our approach enables a new class of time-domain tests of General Relativity, performing a re-analysis of the inspiral-merger-ringdown test on the first observed binary black hole merger. Our investigation demonstrates the feasibility of the Gaussian processes as an alternative to the traditional framework but does not yet establish them as a replacement. Therefore, we conclude with an outlook on the steps needed to realise the full potential of the Gaussian process approach.

The first detection of a gravitational wave (GW) enabled our observation of the Universe through a revolutionary messenger and unveiled phenomena that are occurring in a range of very strong gravitational fields and relativistic velocities. These physical regimes, previously inaccessible to humankind, can now be studied. In particular, the discoveries of an unexpected population of stellar-mass binary black holes (BBH), and unexpected masses for binary neutron star (BNS) components have both pointed to new astrophysics, and to unprecedented tests of the general relativity theory. This thesis focuses on the development of a new method of gravitational wave data analysis, aiming to investigate weak features in the proximity to well-identified BBH merger signals. The method is based on a dedicated version of coherentWaveBurst (cWB), an unmodelled gravitational waves transient search algorithm, developed in the LIGO Scientific Collaboration (LSC) and Virgo Collaboration and widely used on LIGO-Virgo-KAGRA (LVK) data. CoherentWaveBurst relies on the coherent detection of an excess of energy inside the combined data of all the gravitational waves detectors inside the detectors network. Such excess of energy must pass several internal thresholds of the pipeline to be accepted as a possible gravitational wave candidate and these thresholds evaluate not only the strength of the signal with respect to the background noise but also how balanced is the energy distribution among the detectors of the network, its coherence, as well as other quantities whose purpose is to rule out possible outliers due to the presence of non-stationary noise. To develop such a method, it was decided to adopt as science case the search for echoes. In literature, it has been proposed that the gravitational radiation generated from a binary compact objects (CBCs) coalescence might display exotic characteristics if compared to the predicted one generated by black hole-black hole (BH-BH), neutron star-neutron star (NS-NS), or neutron star-black hole (NS-BH) binaries which are, for now, the only detected emitters of gravitational waves. Such differences arise from the proposal that the involved compact objects (COs) of the binary are not standard black holes but instead black hole mimickers called exotic compact objects (ECOs). If this is the case the gravitational wave signal generated from such a binary would display repeated gravitational wave pulses, of widely uncertain morphology, after the merger-ringdown phase of the gravitational signal. These repeated gravitational wave pulses are called echoes, one class of low energetic signals whose presence inside gravitational wave data, this new algorithm is searching for. The proposed data analysis methodology searching for echoes is agnostic over the properties of the predicted gravitational wave pulses emitted by an ECO binary. Indeed, the variety of theoretical alternatives to black holes is not converging over a well-defined post-merger-ringdown signal, each model has its own properties and characteristic features. Therefore, the possibility to investigate the morphological features of possible outliers in the post-merger phase of detected GW signals is fundamental in the process of inferring their nature. Having their morphology recovered without priors makes the proposed search more general than the variety of theoretical models of echoes. This procedure is tested over real data from past LIGO-Virgo observing runs (O1, O2, and O3), and the capability of the search in estimating the main morphological parameters of echoes, such as their arrival time, mean frequency, as well as the amplitude attenuation between subsequent pulses, is investigated. This work concludes that the current state-of-the-art methods and detectors find no evidence for echoes of any morphologies. Such a study extended to lower signal-to-noise ratio (SNR) the detectability of echoes associated with the public gravitational-wave transient catalog of BBH mergers released by the LIGO and Virgo Collaboration. It also sets best quantitative upper limits on the amplitude of low energy signals occurring after the merger-ringdown. To achieve these results, new post-processing tools are developed and optimised to detect and characterize possible energy excess inside a user-defined time window. This required the development of the code and to adapt the cWB infrastructure to the new working requirements which also involves a re-tuning of cWB itself. The optimization of the performances is based on off-source simulations for assessing the detection efficiency and false alarm probability of signal candidates.