Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session R14: Mergers, Collapse and Black Hole Dynamics |
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Sponsoring Units: DGRAV Chair: Scott Noble, The University of Tulsa and Goddard Space Flight Center Room: A226 |
Monday, April 16, 2018 10:45AM - 10:57AM |
R14.00001: Black Hole Dynamics in Einstein-Maxwell-Dilaton-Axion Theory Hyun Lim, Eric Hirschmann, Luis Lehner, Steve Liebling, Carlos Palenzuela Recent detections of gravitational waves from advanced LIGO promise a new channel with which to investigate the universe and test general relativity. In this work, we present black hole dynamics in a modified theory of gravity. Our particular model is Einstein-Maxwell-Dilaton-Axion (EMDA) theory. Using numerical simulations, we investigate dynamical black holes in EMDA theory. We consider a variety of initial data types in order to examine both stability of single black holes in this theory as well as possible alternate scalar and electromagnetic field channels for emission. We also investigate binary black hole mergers in order to probe deviations from the standard gravitational wave signatures of general relativity.~ [Preview Abstract] |
Monday, April 16, 2018 10:57AM - 11:09AM |
R14.00002: Boson Star Mergers as Alternatives to Standard Compact Object Mergers Steven Liebling Instead of studying an alternative to general relativity, one can instead consider boson stars as an alternative model. In particular, for certain potentials, boson stars have compactnesses that approach those of black holes. We evolve very compact boson stars constructed with a solitonic potential in orbit through merger and study the resulting gravitational waves for comparison to those of black hole binaries and neutron star binaries. [Preview Abstract] |
Monday, April 16, 2018 11:09AM - 11:21AM |
R14.00003: The superradiant instability of massive vector fields around spinning black holes William East, Frans Pretorius In the presence of a massive bosonic field, spinning black holes are in fact unstable to superradiance. This leads to the exciting possibility that observations of astrophysical black holes can be used to probe the existence of axions, dark photons, or other ultralight bosons with Compton wavelength comparable to the black hole's radius. Focusing on the specific case of a massive vector field, I will present results on the linear growth and subsequent nonlinear behavior of the superradiant instability. In particular, we find that the instability smoothly saturates when the black hole has lost sufficient rotational energy for it's horizon frequency to the match the frequency of the bosonic cloud that spontaneously forms around it. I will also describe the gravitational wave signal produced by such an oscillating cloud, which could be a potential target for LIGO. [Preview Abstract] |
Monday, April 16, 2018 11:21AM - 11:33AM |
R14.00004: Abstract Withdrawn
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Monday, April 16, 2018 11:33AM - 11:45AM |
R14.00005: Cauchy-horizon singularity inside perturbed Kerr black holes revisited Gaurav Khanna, Lior Burko, Anil Zenginovglu The Cauchy horizon inside a perturbed Kerr black hole develops an instability that transforms it into a curvature singularity. We solve for the linearized Weyl scalars $\psi_0$ and $\psi_4$ and for the curvature scalar $R_{\alpha\beta\gamma\delta}R^{\alpha\beta\gamma\delta}$ along outgoing null rays approaching the Cauchy horizon in the interior using the Teukolsky equation, and compare our results with those found in perturbation analysis. Two technological improvements on our code allow us to obtain results in better agreement with perturbation analysis: (1) The fields are ``evolved'' on the inner boundary as opposed to computed using the boundary conditions in conjunction with data from the ``bulk,'' and (2) we use a fifth-order WENO finite-difference scheme with third-order Shu-Osher explicit time-stepping. Our results corroborate the perturbation analysis result that at its early parts the Cauchy horizon evolves into a deformationally-weak, null, scalar-curvature singularity. We further find the first numerical confirmation for the perturbative results for $\psi_0(u={\rm const},v)$, $\psi_4(u={\rm const},v)$, and for $R_{\alpha\beta\gamma\delta}R^{\alpha\beta\gamma\delta}(u={\rm const},v)$, where $u,v$ are retarded and advanced times, respectively. [Preview Abstract] |
Monday, April 16, 2018 11:45AM - 11:57AM |
R14.00006: Linearized Stability of Extreme Black Holes Lior M. Burko, Gaurav Khanna Extreme black holes have been argued to be unstable, in the sense that under linearized gravitational perturbations of the extreme Kerr spacetime the Weyl scalar $\psi_4$ blows up along their event horizons at very late advanced times. We show numerically, by solving the Teukolsky equation in 2+1D, that all algebraically-independent curvature scalar polynomials approach limits that exist when advanced time along the event horizon approaches infinity. Therefore, the horizons of extreme black holes are stable against linearized gravitational perturbations. We argue that the divergence of $\psi_4$ is a consequence of the choice of a fixed tetrad, and that in a suitable dynamical tetrad all Weyl scalars, including $\psi_4$, approach their background extreme Kerr values. We make similar conclusions also for the case of scalar field perturbations of extreme Kerr. [Preview Abstract] |
Monday, April 16, 2018 11:57AM - 12:09PM |
R14.00007: The Affine-Null Formulation Of The Gravitational Equations: Spherical Critical Collapse Jeffrey Winicour, J. A. Crespo, H. P. de Oliveira A new evolution algorithm for the characteristic initial value problem based upon an affine parameter rather than the areal radial coordinate used in the Bondi-Sachs formulation is applied in the spherically symmetric case to the gravitational collapse of a massless scalar field. The advantages over the Bondi-Sachs version are discussed, with particular emphasis on the application to critical collapse. Unexpected quadratures lead to an evolution algorithm based upon two first order equations which can be integrated along the null rays. It is implemented as a global numerical evolution code based upon the Galerkin method. New results regarding the global properties of critical collapse are presented. [Preview Abstract] |
Monday, April 16, 2018 12:09PM - 12:21PM |
R14.00008: Critical Collapse of a Massless Scalar Field in 3+1D General Relativity Nils Deppe We present results from the first study of critical behavior in 3-d gravitational collapse. The source of the gravitational field is a massless scalar field. This is a well-studied case for spherically symmetric gravitational collapse, allowing us to understand the reliability and accuracy of the simulations. We study both supercritical and subcritical evolutions to see if one provides more accurate results than the other. Specifically, we address the open question of whether or not the spherical mode dominates in the gravitational collapse of generic 3-d initial data. In addition to observing the expected critical behavior, we are able to observe fine structure that has not been well studied beyond spherical symmetry. [Preview Abstract] |
Monday, April 16, 2018 12:21PM - 12:33PM |
R14.00009: Non-Spherically Symmetric Collapse in Asymptotically AdS Spacetimes Hans Bantilan, Pau Figueras, Markus Kunesch, Paul Romatschke We numerically simulate gravitational collapse in asymptotically anti-de Sitter spacetimes away from spherical symmetry. Starting from initial data sourced by a massless real scalar field, we solve the Einstein equations with a negative cosmological constant in five spacetime dimensions and obtain a family of non-spherically symmetric solutions, including those that form two distinct black holes on the axis. We find that these configurations collapse faster than spherically symmetric ones of the same mass and radial compactness. Similarly, they require less mass to collapse within a fixed time. [Preview Abstract] |
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