Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session H15: Simulations of Binary Black Hole MergersRecordings Available

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Sponsoring Units: DGRAV Chair: Pablo Laguna, University of Texas at Austin Room: Marquis C 
Sunday, April 10, 2022 10:45AM  10:57AM 
H15.00001: Challenges in Numerical Relativity: Intermediate massratio binaries David W Neilsen, Eric Hirschmann, Milinda Fernando, Hari Sundar, Yosef Zlochower As gravitational wave detectors continually improve, numerical relativists must also improve their methods to generate wavesforms of sufficient accuracy for gravitational wave analysis and tests of general relativity. The large computational cost in generating waveforms comes from both the high level of adaptability needed for intermediate massratio black hole binaries, as well as the long runtimes that are needed to produce waveforms that can be matched to postNewtonian waveforms. DendroGR is a new computer code for solving the Einstein equations, which was designed to anticipate some of these challenges. DendroGR solves the Einstein equations on an unstructured grid using waveletbased refinement. It has achieved high scalability and computational performance with binary black hole runs up to mass ratio $q=32$, and results of these simulations will be presented. We will also discuss new directions to further improve DendroGR's computational performance, such as new methods for time adaptivity and improved finitedifference stencils. Some initial results of these tests will be presented. 
Sunday, April 10, 2022 10:57AM  11:09AM 
H15.00002: Exploring the small mass ratio binary black hole merger with Numerical Relativity Carlos O Lousto, James Healy, Nicole C Rosato We perform a sequence of binary black hole simulations with increasingly small mass ratios, reaching to a 128:1 binary that displays 13 orbits before merger. Based on a detailed convergence study of the $q=m_1/m_2=1/15$ nonspinning case, we apply additional mesh refinements levels around the smaller hole horizon to reach successively the $q=1/32$, $q=1/64$, and $q=1/128$ cases. Roughly a linear computational resources scaling with $1/q$ is observed on 8nodes simulations. We compute the remnant properties of the merger: final mass, spin, and recoil velocity, finding precise consistency between horizon and radiation measures. We also compute the gravitational waveforms: its peak frequency, amplitude, and luminosity. We compare those values with predictions of the corresponding phenomenological formulas, reproducing the particle limit within 2\%, and we then use the new results to improve their fitting coefficients. 
Sunday, April 10, 2022 11:09AM  11:21AM 
H15.00003: Simulations of Supermassive Binary Black Hole: Accretion Dynamics in the Spinning case Jesús M RuedaBecerril, Mark J Avara, Federico G Lopez Armengol, Luciano M Combi, Manuela Campanelli In recent years, numerical methods have been used to model supermassive black hole binaries with the purpose of identifying the properties and signatures of these systems. Here we present 3DMHD simulations of spinning binary black holes with the use of the multimesh/multiphysics code PatchworkMHD, capable of evolving different physical regions with different mesh topologies. This new infrastructure has allowed to accurately resolve complicated system such as supermassive black holes surrounded by a circumbinary disk. With a new prescription of a dynamic spacetime, and trajectories for spinning black hole binary, we present new simulations showing the influence of the spin in binary environment, including the formation of minidisks and jets. 
Sunday, April 10, 2022 11:21AM  11:33AM 
H15.00004: Status of binaryblackhole simulations with SpECTRE Geoffrey Lovelace Nextgeneration gravitationalwave detectors will observe binary black holes with unprecedented fidelity. To avoid introducing bias when interpreting these observations, numericalrelativity models of binary black holes will need to achieve an order of magnitude higher accuracy than today's state of the art. One promising avenue for achieving this accuracy is nextgeneration numerical relativity codes designed to leverage the exascale computing resources expected in the next decade. In this talk, I will discuss progress toward enabling SpECTRE, a nextgeneration numericalrelativity code being developed by the SXS Collaboration, to simulate binary black holes. 
Sunday, April 10, 2022 11:33AM  11:45AM 
H15.00005: Isometric Embedding and Visualization of the Apparent Horizons in Binary Black Hole Simulations Hengrui Zhu, Robert P Owen We present an efficient algorithm for embedding topological twospheres with specified 2metrics into threedimensional Euclidean space. We show that the algorithm converges for a large class of test surfaces with known embeddings, even for those with negative Gaussian curvature, independent of the initial guess. The algorithm is then applied to visualize the apparent horizons in numerical binary black hole simulations using the Spectral Einstein Code (SpEC). This algorithm also allows one to test various definitions for Quasilocal mass in general relativity and study the energy dynamics during black hole mergers. 
Sunday, April 10, 2022 11:45AM  11:57AM 
H15.00006: Fundamental physics probed via highenergy collisions of electrically charged black holes Gabriele Bozzola, Vasileios Paschalidis Ultrarelativistic collisions of black holes are ideal settings where to investigate how general relativity behaves under extreme conditions. A large fraction of the allowed parameter space has been explored over the past 13 years (including mass, spin, impact parameter), with the notable exception of charge. The inclusion of charge is significant because it adds non trivial degrees of freedom to the system. For example, charge constitutes another way to reach extremality (together with spin) and opens up a new channel to radiate away energy (through electromagnetic waves). Moreover, charge makes the study more directly relevant to particle physics and the production of microscopic black holes in cosmic rays and in particle accelerators. In this talk, I am going to present the first numericalrelativity simulations of headon collisions of black holes with the same charge and mass. In particular, I am going to discuss what they can teach us about a variety of conjectures, including cosmic censorship and the role of the inner structure of bodies colliding at relativistic speed. 
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