We present the first analytical inspiral-merger-ringdown gravitational waveforms from binary black holes (BBHs) with nonprecessing spins, that is based on a description of the late-inspiral, merger ...and ringdown in full general relativity. By matching a post-Newtonian description of the inspiral to a set of numerical-relativity simulations, we obtain a waveform family with a conveniently small number of physical parameters. These waveforms will allow us to detect a larger parameter space of BBH coalescence, including a considerable fraction of precessing binaries in the comparable-mass regime, thus significantly improving the expected detection rates.
ABSTRACT
Along their path from source to observer, gravitational waves may be gravitationally lensed by massive objects leading to distortion in the signals. Searches for these distortions amongst ...the observed signals from the current detector network have already been carried out, though there have as yet been no confident detections. However, predictions of the observation rate of lensing suggest detection in the future is a realistic possibility. Therefore, preparations need to be made to thoroughly investigate the candidate lensed signals. In this work, we present some follow-up analyses that could be applied to assess the significance of such events and ascertain what information may be extracted about the lens-source system by applying these analyses to a number of O3 candidate events, even if these signals did not yield a high significance for any of the lensing hypotheses. These analyses cover the strong lensing, millilensing, and microlensing regimes. Applying these additional analyses does not lead to any additional evidence for lensing in the candidates that have been examined. However, it does provide important insight into potential avenues to deal with high-significance candidates in future observations.
These notes summarize basic concepts underlying numerical relativity and in particular the numerical modeling of black hole dynamics as a source of gravitational waves. Main topics are the 3+1 ...decomposition of general relativity, the concept of a well-posed initial value problem, the construction of initial data for general relativity, trapped surfaces and gravitational waves. Also, a brief summary is given of recent progress regarding the numerical evolution of black hole binary systems.
Motivated by the problem of solving the Einstein equations, we discuss high order finite difference discretizations of first order in time, second order in space hyperbolic systems. Particular ...attention is paid to the case when first order derivatives that can be identified with advection terms are approximated with non-centered finite difference operators. We first derive general properties of these discrete operators, then we extend a known result on numerical stability for such systems to general order of accuracy. As an application we analyze the shifted wave equation, including the behavior of the numerical phase and group speeds at different orders of approximations. Special attention is paid to when the use of off-centered schemes improves the accuracy over the centered schemes.
Economic development and environmental conservation are often seen as opposing forces in the arena of government policy-making. With more than 7 million people and a rich diversity of marine species ...and habitats, Hong Kong is an excellent case study to explore this dynamic. Despite anthropogenic impacts, Hong Kong still hosts more than 90 species of stony corals within a marine area of 1650 km
2
. This is remarkable in light of the global plight of coral reefs, which have been reduced by ~80% worldwide in recent decades. The Hong Kong Special Administrative Region has not been immune to this negative trend with an unfortunate track of marine environmental disasters and, as such, can be viewed a harbinger for the future trajectory of coral reefs worldwide. Yet, the story is not entirely negative. Hong Kong possesses key assets, including capable government environmental agencies and competitive research led by local universities, which can bring novel and promising approaches for coral biodiversity conservation in an urbanized context. To coordinate and assist conservation efforts in Hong Kong, we here identify and prioritize major management efforts and identify knowledge gaps for coral conservation based on updated coral biodiversity distribution and a current literature review. Specifically, we propose five priorities for the most positive impact on conservation efforts: (1) reconstruct environmental baselines and establish long-term monitoring of local coral communities, (2) enhance the management and protection of local coral habitats, (3) improve water quality, (4) gain an understanding of the genetic connectivity among local and distant coral communities, and finally, (5) establish an active restoration program for local coral species/communities. In order to build progressive and integrative management strategies for coral biodiversity conservation in Hong Kong, we suggest specific ways in which these priorities be addressed and encourage a fresh dialogue between the government, the public and academia.
We extend the notion of numerical stability of finite difference approximations to include hyperbolic systems that are first order in time and second order in space, such as those that appear in ...numerical relativity and, more generally, in Hamiltonian formulations of field theories. By analyzing the symbol of the second order system, we obtain necessary and sufficient conditions for stability in a discrete norm containing one-sided difference operators. We prove stability for certain toy models and the linearized Nagy–Ortiz–Reula formulation of Einstein’s equations.
We also find that, unlike in the fully first order case, standard discretizations of some well-posed problems lead to unstable schemes and that the Courant limits are not always simply related to the characteristic speeds of the continuum problem. Finally, we propose methods for testing stability for second order in space hyperbolic systems.
ABSTRACT
Gravitational waves provide a unique tool for observational astronomy. While the first LIGO–Virgo catalogue of gravitational-wave transients (GWTC-1) contains 11 signals from black hole and ...neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. To extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. In a previous paper, we introduced bilby: a modular and user-friendly Bayesian inference library adapted to address the needs of gravitational-wave inference. In this work, we demonstrate that bilby produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the 11 GWTC-1 signals. Additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. This work establishes that bilby is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals.
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