Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session R7: Force-Free Electrodynamics and Fluid Models |
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Sponsoring Units: GGR Chair: Tony Chu, Princeton University Room: Key 3 |
Monday, April 13, 2015 10:45AM - 10:57AM |
R7.00001: Exact force-free electrodynamic solutions and their perturbations Fan Zhang, Luis Lehner, Sean McWilliams, Harald Pfeiffer, Huan Yang This talk is an amalgamation of several works relating to finding exact force-free electrodynamic (FFE) solutions and examining their behaviour under perturbations, both analytically and numerically. The talk will briefly discuss technical points such as the choice of numerical FFE evolution systems and challenges posed by light surfaces when seeking analytical FFE solutions, presenting along the way a couple of new solutions in the near horizon extreme Kerr spacetime. It will then move on to present the mode structure of the perturbed Blandford-Znajek solution and some results concerning the stability of a family of exact propagating FFE solutions. [Preview Abstract] |
Monday, April 13, 2015 10:57AM - 11:09AM |
R7.00002: Exact Solutions for Extreme Black Hole Magnetospheres Maria J. Rodriguez, Alexandru Lupsasca, Andrew Strominger Plasma-filled magnetospheres can extract energy from a spinning black hole and provide the power source for a variety of observed astrophysical phenomena. These magnetospheres are described by the highly nonlinear equations of force-free electrodynamics, or FFE. Typically these equations can only be solved numerically. In this talk I will explain how to analytically obtain several infinite families of exact solutions of the full nonlinear FFE equations very near the horizon of a maximally spinning black hole, where the energy extraction takes place. [Preview Abstract] |
Monday, April 13, 2015 11:09AM - 11:21AM |
R7.00003: New exact force-free magnetospheres and an AGN model Alexandru Lupsasca, Sam Gralla, Maria Rodriguez We recast the equations for a stationary axisymmetric force-free magnetosphere in the form of an equation for the poloidal field lines. This formulation enables us to find new exact solutions in flat spacetime, including one whose geometry closely resembles that of an active galactic nucleus. We then use this solution to model jet formation and energy extraction from a slowly spinning black hole. [Preview Abstract] |
Monday, April 13, 2015 11:21AM - 11:33AM |
R7.00004: Force-free electrodynamics in a Kerr background: Explicit solutions Govind Menon After a brief introduction to the equations of electrodynamics in a curved spacetime in the 3$+$1 formalism, solutions consistent with the Blandford-Znajek process will be presented in detail. Possible astrophysical implications of these solutions will also be discussed. [Preview Abstract] |
Monday, April 13, 2015 11:33AM - 11:45AM |
R7.00005: Coupled Oscillator Model for Nonlinear Gravitational Perturbations Huan Yang, Fan Zhang, Stephen Green, Luis Lehner Motivated by the fluid/gravity correspondence, we introduce a new method for characterizing nonlinear gravitational interactions. Namely we map the nonlinear perturbative form of the Einstein's equation to the equations of motion of a series of nonlinearly-coupled harmonic oscillators. These oscillators correspond to the quasinormal modes of the background spacetime. We demonstrate the mechanics and the utility of this formalism with an asymptotically AdS black-brane spacetime, where the equations of motion for the oscillators are shown to be equivalent to the Navier-Stokes equation for the boundary fluid in the mode-expansion picture. We thereby expand on the explicit correspondence connecting the fluid and gravity sides for this particular physical set-up. Perhaps more importantly, we expect this formalism to remain valid in more general spacetimes, including those without a fluid/gravity correspondence. In other words, although born out of the correspondence, the formalism survives independently of it and has a much wider range of applicability. [Preview Abstract] |
Monday, April 13, 2015 11:45AM - 11:57AM |
R7.00006: Forced Turbulence in Relativistic Conformal Fluids John Ryan Westernacher-Schneider, Stephen Green, Luis Lehner, Kipp Canon, Yaron Oz Given the renewed interest arising both from AdS/CFT and astrophysics, we revisit the phenomenon of relativistic turbulence. We build on some recent work which extends known non-relativistic results in turbulence to the case of relativistic (and thus compressible) fluids. In particular, we derive the scaling behaviour of two-point correlation functions in 2+1 dimensions---holographically dual to 3+1 dimensional gravity. Turbulence in 2+1 dimensions also approximates several astrophysical situations, such as thin accretion disks around black holes. We perform numerical simulations of forced steady-state turbulence to verify our derived correlation functions. [Preview Abstract] |
Monday, April 13, 2015 11:57AM - 12:09PM |
R7.00007: Challenging the standard perfect fluid paradigm James O'Brien We show that the standard perfect fluid paradigm is not necessarily a valid description of a curved space steady state gravitational source. Simply by virtue of not being flat, curved space geometries have to possess intrinsic length scales, and such length scales can affect the fluid structure.We show that for the specific case of a static, spherically symmetric geometry, the steady state energy-momentum tensor that ensues will in general be of the form $T_{\mu\nu}=(\rho+p)U_{\mu}U_{\nu}+pg_{\mu\nu}+q\pi_{\mu\nu}$ where $\pi_{\mu\nu}$ is a symmetric, traceless rank two tensor which obeys $U^{\mu}\pi_{\mu\nu}=0$. Such a $q\pi_{\mu\nu}$ type term is absent for an incoherently averaged steady state fluid in a spacetime where there are no intrinsic length scales, and in principle would thus be missed in a covariantizing of a flat spacetime $T_{\mu\nu}$. While it is reassuring that we find that in practice the effect of such $q\pi_{\mu\nu}$ type terms is small for weak gravity stars, for strong gravity systems their potential influence would need to be explored. [Preview Abstract] |
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