Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session X6: Binary Black Holes: Spins and Kicks |
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Sponsoring Units: GGR Chair: Mark Scheel, California Institute of Technology Room: Key 2 |
Tuesday, April 14, 2015 10:45AM - 10:57AM |
X6.00001: Accurate Models for Astrophysical Black Hole Recoils Yosef Zlochower, Carlos Lousto When black-hole binaries merge, an intense, asymmetrical burst of radiation can cause the remnant to recoil at thousands of kilometers a second, large enough to eject the remnant black hole out of the host galaxy. The actual recoil will depend on the size and orientation of the black-hole spins and the mass ratio of the binary. Modeling the recoil for this seven dimensional parameters space can be prohibitively expensive. However, careful choices of configurations can be used to model the recoil for a broad class of astrophysically important binaries. Here we describe the results from a large set of new simulations which we use to develop several interpolative formulas for the recoil that are accurate over a broad range of mass ratios and spins. [Preview Abstract] |
Tuesday, April 14, 2015 10:57AM - 11:09AM |
X6.00002: Remnant mass, spin, and recoil from spin aligned black-hole binaries James Healy, Carlos Lousto, Yosef Zlochower We perform a set of 36 nonprecessing black-hole binary simulations with spins either aligned or counteraligned with the orbital angular momentum in order to model the final mass, spin, and recoil of the merged black hole as a function of the individual black hole spin magnitudes and the mass ratio of the progenitors. We find that the maximum recoil for these configurations is $V_{max}=526\pm23$ km/s, which occurs when the progenitor spins are maximal, the mass ratio is $q_{max}=m_1/m_2=0.623\pm0.038$, the smaller black-hole spin is aligned with the orbital angular momentum, and the larger black-hole spin is counteraligned ($\alpha_1=-\alpha_2=1$). This maximum recoil is about $80$ km/s larger than previous estimates. We provide explicit phenomenological formulas for the final mass, spin, and recoil as a function of the individual BH spins and the mass difference between the two black holes. [Preview Abstract] |
Tuesday, April 14, 2015 11:09AM - 11:21AM |
X6.00003: Genuine Spin-Flip in Binary Black Holes Carlos Lousto, James Healy We perform a full numerical simulation of binary spinning black holes to display the long term spin dynamics. We start the simulation at an initial proper separation between the equal mass holes of $d\approx25M$ and evolve them down to merger for nearly 48 orbits, 3 precession cycles and half of a flip-flop cycle. The simulation lasts for $t=20000M$ and displays a change in the orientation of the spin of the black holes with one of them going from initially aligned with the orbital angular momentum to a complete anti-alignment after half of a flip-flop cycle. We compare this evolution with an integration of the 3.5 Post-Newtonian equations of motion and spin evolution to show that this process continuously flip-flops the spin during the lifetime of the binary until merger. We also provide lower order analytic expressions for the maximum flip-flop angle and frequency. We discuss the effects on spin growth in accreting binaries and the observational consequences for galactic and supermassive binary black holes. [Preview Abstract] |
Tuesday, April 14, 2015 11:21AM - 11:33AM |
X6.00004: Defining and calculating spin on deformed apparent horizons Robert Owen Numerical relativity, apart from its significance to gravitational wave science, also provides a testing ground for studying the properties of spacetime in the highly dynamical, nonlinear regime. Many interesting aspects of black hole physics relate to spin angular momentum. Despite its intuitive power, angular momentum is a notoriously tricky concept to define in general relativity, and mathematical subtleties still cloud the interpretation of black hole spin in situations of most interest to numerical relativity. In this talk, I will describe a few such ambiguities, characterize the practical danger that they might pose, and explore a few options for mitigating them. Along the way, I will describe a measure of black hole extremality, derived from ideas of Booth and Fairhurst, that can help characterize the spin of arbitrarily deformed black holes. [Preview Abstract] |
Tuesday, April 14, 2015 11:33AM - 11:45AM |
X6.00005: Nearly extremal apparent horizons in simulations of merging black holes Geoffrey Lovelace, Mark Scheel, Robert Owen, Matthew Giesler, Reza Katebi, Bela Szilagyi, Tony Chu, Nicholas Demos, Daniel Hemberger, Lawrence Kidder, Harald Pfeiffer, Nousha Afshari The spin $S$ of a Kerr black hole is bounded by the surface area $A$ of its apparent horizon: $8\pi S \le A$. We present recent results (arXiv:1411.7297) for the extremality of apparent horizons for merging, rapidly rotating black holes with equal masses and equal spins aligned with the orbital angular momentum. Measuring the area and (using approximate Killing vectors) the spin on the individual and common apparent horizons, we find that the inequality $8\pi S < A$ is satisfied but is very close to equality on the common apparent horizon at the instant it first appears---even for initial spins as large as $S/M^2=0.994$. We compute the smallest value $e_0$ that Booth and Fairhurst's extremality parameter can take for any scaling of the horizon's null normal vectors, concluding that the common horizons are at least moderately close to extremal just after they appear. We construct binary-black-hole initial data with marginally trapped surfaces with $8\pi S > A$ and $e_0>1$, but these surfaces are always surrounded by apparent horizons with $8\pi S [Preview Abstract] |
Tuesday, April 14, 2015 11:45AM - 11:57AM |
X6.00006: Simulations of nearly extremal binary black holes Matthew Giesler, Mark Scheel, Daniel Hemberger, Geoffrey Lovelace, Kevin Kuper, Michael Boyle, Bela Szilagyi, Lawrence Kidder Astrophysical black holes could have nearly extremal spins; therefore, nearly extremal black holes could be among the binaries that current and future gravitational-wave observatories will detect. Predicting the gravitational waves emitted by merging black holes requires numerical-relativity simulations, but these simulations are especially challenging when one or both holes have mass $m$ and spin $S$ exceeding the Bowen-York limit of $S/m^2=0.93$. Using improved methods we simulate an unequal-mass, precessing binary black hole coalescence, where the larger black hole has $S/m^2=0.99$. We also use these methods to simulate a nearly extremal non-precessing binary black hole coalescence, where both black holes have $S/m^2=0.994$, nearly reaching the Novikov-Thorne upper bound for holes spun up by thin accretion disks. We demonstrate numerical convergence and estimate the numerical errors of the waveforms; we compare numerical waveforms from our simulations with post-Newtonian and effective-one-body waveforms; and we compare the evolution of the black-hole masses and spins with analytic predictions. [Preview Abstract] |
Tuesday, April 14, 2015 11:57AM - 12:09PM |
X6.00007: Force-free electrodynamics in dynamical curved spacetimes Sean McWilliams We present results on our study of force-free electrodynamics in curved spacetimes. Specifically, we present several improvements to what has become the established set of evolution equations, and we apply these to study the nonlinear stability of analytically known force-free solutions for the first time. We implement our method in a new pseudo-spectral code built on top of the SpEC code for evolving dynamic spacetimes. Finally, we revisit these known solutions and attempt to clarify some interesting properties that render them analytically tractable. Finally, we preview some new work that similarly revisits the established approach to solving another problem in numerical relativity: the post-merger recoil from asymmetric gravitational-wave emission. These new results may have significant implications for the parameter dependence of recoils, and consequently on the statistical expectations for recoil velocities of merged systems. [Preview Abstract] |
Tuesday, April 14, 2015 12:09PM - 12:21PM |
X6.00008: Global Aspects of Radiation Memory Jeffrey Winicour The gravitational radiation memory effect produces a net displacement of test particles. The proposed sources lead to E mode memory, as characterized by an even parity polarization pattern. Although odd parity, or B mode, radiation memory is mathematically possible, no physically realistic source has been identified. There is an electromagnetic counterpart to radiation memory which produces a net momentum ``kick'' of charged test particles. A global null cone treatment shows that electromagnetic E mode memory requires unbounded charges and no physically realistic source produces B mode memory. A compelling theoretical aspect of E mode gravitational radiation memory is related to the supertranslations in the Bondi-Metzner-Sachs (BMS) asymptotic symmetry group. For a stationary system, supertranslations can be eliminated and the BMS group reduced to the Poincare group, for which angular momentum is well-defined. However, for a stationary to stationary transition, the two Poincare groups obtained at early and late times differ by a supertranslation if the gravitational radiation has nonzero E mode memory. This suggests a distinctly general relativistic mechanism for angular momentum loss and presents a ripe problem for the numerical simulation of high spin black hole binaries. [Preview Abstract] |
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