Session H16: Numerical Modeling of Binary Black Holes

Live

Gravitational memory is a phenomenon induced by the passage of gravitational waves that corresponds to persistent, physical changes to spacetime. We present advances in resolving the two primary gravitational memory effects---displacement and spin memory---in numerical simulations of binary black hole mergers produced by SXS's Spectral Einstein Code. We show that the waveforms extracted using Cauchy-characteristic extraction (CCE) obey the Bondi-Metzner-Sachs (BMS) balance laws to a high degree of accuracy, unlike previous waveforms produced by numerical relativity simulations. We also show that the waveforms in all publicly available waveform catalogs, which do not exhibit memory effects, can be corrected to include such features.   

Live

During a binary black merger, event horizons evolve via the ``pair of pants’’ diagram. This has now been understood for five decades. However the full equivalent diagram for apparent horizons, and in particular the ultimate fate of the original apparent horizon of each black hole, remained unresolved. Very recently, significant progress has been made on this problem. In this talk I will present the complete evolution of the horizons traced out by all marginally outer trapped surfaces (MOTS) during an axisymmetric black hole merger. The evolution is much more interesting and intricate than that for event horizons. The progress was made possible by the application of new MOTS-finding techniques and the behaviours of the various horizons is elucidated by an analysis of the MOTS stability spectrum.   

Live

Numerical-relativity calculations of binary black holes are crucial tools for modeling and interpreting gravitational-wave observations. Future gravitational-wave observatories on Earth and in space will require waveform models that are much more accurate than numerical relativity can currently achieve. SpECTRE is a next-generation numerical-relativity code that aims to achieve much greater accuracy than is possible today, by employing techniques such as adopting a Discontinuous Galerkin method and task-based parallelism. In this talk, I will discuss progress toward SpECTRE's first simulations of merging black holes.   

Live

SpECTRE is a next-generation numerical-relativity code (currently under development) that will calculate the gravitational waves emitted by colliding black holes and neutron stars with unprecedented accuracy, by using novel techniques that enable it to scale to hundreds of thousands of compute cores. These high-accuracy calculations will help scientists interpret observations from next-generation gravitational-wave detectors. I will discuss the completion of SpECTRE's computational infrastructure to measure the properties of black hole's horizons, such as the black hole's masses and spin angular momenta, which are especially important for connecting the calculations to observations. Specifically, I will present results assessing the accuracy that SpECTRE is able to achieve, and I will compare the results to those from the Spectral Einstein Code (SpEC), a current-generation numerical relativity code.   

Live

Generic binary black hole (BBH) mergers may occur in elliptical orbits with non-zero eccentricity. The waveform models used by the LIGO and Virgo collaboration so far to detect and estimate parameters of gravitational wave (GW) signals are based on the assumption of quasicircular orbits. In the recent years there has been an increasing effort from the GW community to model eccentric BBHs. The first step required to model such systems is the generation of a data set of eccentric numerical relativity (NR) simulations which can be used to calibrate and validate the eccentric waveform models, and test data analysis implications for such waveforms. First, the state of art of the current eccentric NR data sets will be reviewed. Next, we will show the adaption of the spectral NR code, SpEC, to produce a set of long and highly accurate eccentric nonspinning NR simulations from mass ratio 1 to 10. The accuracy of these new waveforms is assessed by showing convergence tests and computing the unfaithulness between waveforms at different resolutions. Finally, we briefly show possible applications of these longer and more accurate waveforms to waveform modelling or data analysis studies, like parameter estimation or searches.   

Live

Much of gravitational wave (GW) science depends on GW observations being compared with millions of theoretical predictions generated by GW approximants. Our most reliable approximants are built upon GW catalogs extracted from numerical relativity (NR) simulations, which solve Einstein's equations in full. To date each of these NR simulations has required a small computing cluster, which has limited throughput to only about 3,000 GWs in 15 years. Given the vast parameter space of even the simplest observed GW source---binary black holes (BBHs)---such a small GW collection threatens potential science gains from future GW observations. BlackHoles@Home is a proposed BOINC-based citizen-science project leveraging new techniques to fit NR BBH simulations on a consumer-grade desktop computer, enabling GW follow-ups and catalogs with unprecedented throughput using volunteer computers. We recently demonstrated that our techniques enable the final orbits of a BBH and post-merger to be calculated on a cellphone in full NR, with accurate GWs. We report on our latest improvements, which indicate we are on track to launch BlackHoles@Home within months.   

Live

The loss of linear momentum carried away by gravitational waves in the coalescence of binary black holes inflicts a kick on the final black hole. The effect has been mostly studied for black holes merging in vacuum. We investigate the kick on the final black hole when the binary is immersed in a cloud of scalar field. We present results from two types of binaries: non-spinning, unequal-mass systems and systems with equal mass holes with anti-aligned spins perpendicular to the orbital plane. We find that the scalar field attenuates the kick of the final remnant black hole in all the studied cases.   

Live

We explore different gauge choices in the moving puncture formulation in order to improve the accuracy of a linear momentum measure evaluated on the horizon of the remnant black hole produced by the merger of a binary.In this talk, we will investigate gauges in which the parameter $m\eta$, which damps oscillations in the shift equation, takes on decreasing constant values. These alternative gauges are used to do an in-depth study of a $q=m_2/m_1=1/3$ binary in which it is determined that choosing an $m\eta$ at 1 produces the most accurate measure of recoil velocity when compared to the evaluation of the radiated linear momentum at infinity for typical numerical resolutions.This result is then confirmed with alternative comparable-mass, nonspinning binaries$q=1/2$ and $q=1/5$ as well as an equal mass binary with dimensionless spin of 0.8.   

On Demand

Binary black hole systems with constituents that have very different masses are a subset of the binary population that, from a computational perspective, are more challenging to simulate than equal or near equal mass binaries. Their resource demands are significant and it is broadly understood that their successful evolution will require particular approaches and methods that are tuned to this region of the parameter space. We combine two such approaches, namely a parallel octree-refined adaptive mesh and a wavelet adaptive multiresolution method to produce the mesh. This highly scalable framework permits the efficient and rapid simulation of such intermediate mass ratio inspirals (IMRIs). We present some results from these efforts that have proven successful in simulating binaries with larger mass ratios.