Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session E8: Black Holes in Astrophysics |
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Sponsoring Units: DAP Chair: Sharon Morsink, University of Alberta Room: 202 |
Saturday, April 5, 2014 3:30PM - 3:42PM |
E8.00001: Electron-positron cascade in magnetospheres of spinning black holes Alex Ford, Brett Keenan, Mikhail V. Medvedev We study the magnetospheres of spinning black holes (BHs) in active Galactic Nuclei (AGN), quasars, blazars and such. It is believed that spinning BHs in ambient magnetic fields develop force-free magnetospheres. Their structure should determine how relativistic jets are launched and how the BH energy is extracted, e.g., via Blandford-Znajek mechanism. The key assumption for the force-free condition is the presence of plasma with the density being above the Goldreigh-Julian density. Unlike NSs which can in principle supply electrons from the surface, BH cannot supply plasma at all. The plasma must be generated {\it in situ} via an electron-positron cascade, presumably in the gap region. Here we study such pair cascade and find the conditions under which it can occur and, hence, AGN and quasar/blazar jets can exist. [Preview Abstract] |
Saturday, April 5, 2014 3:42PM - 3:54PM |
E8.00002: Wavefront twisting by rotating back holes: orbital angular momentum generation and phase coherent detection Huan Yang In this work we study the wave propagation and scattering near a rotating black hole. In particular, we assume a coherent emission source near the black hole, and investigate the wavefront distortion as seen by a distant observer. Near the observer, the propagating wave can be decomposed using the Laguerre-Gaussian mode basis, and its wavefront distortion can be characterized by the decomposition coefficient. We find that this decomposition spectrum is symmetric for wave sources located near a Schwarzschild black hole, but is generically asymmetric if the host black hole is rotating. The spectrum asymmetry, or the net orbital angular momentum carried by the wave, is intimately related with the black hole spin, mass, the wave frequency, the source location as well as the observer's location. We present semi-analytical expressions and numerical results of these parameter-dependences, which suggest that the black-hole-induced spectrum asymmetry is generally too weak to be observed in radio astronomy. [Preview Abstract] |
Saturday, April 5, 2014 3:54PM - 4:06PM |
E8.00003: Searching for Toroidal Event Horizons in Binary Black Hole Mergers Andy Bohn We find event horizons of binary black hole (BBH) mergers, produced using the Spectral Einstein Code (SpEC), and explore their topologies. When the BBH merger does not exhibit spatial symmetry, we expect the spatial cross sections of the event horizon to go through a toroidal topology. However, we find no evidence of a toroidal phase using the spatial slicing of the SpEC simulations, generalized harmonic gauge, to the accuracy of our event horizon finder. To further explore the $2+1$ dimensional event horizon hypersurface, we re-slice the event horizons in an affine slicing to look for a toroidal phase. [Preview Abstract] |
Saturday, April 5, 2014 4:06PM - 4:18PM |
E8.00004: Accretion disks around binary black holes of unequal mass: GRMHD simulations near decoupling Roman Gold, Vasileios Paschalidis, Zachariah Etienne, Stuart Shapiro, Harald Pfeiffer We report on simulations in general relativity of magnetized disks accreting onto black hole binaries. We vary the binary mass ratio from 1:1 to 1:10 and evolve the systems when they orbit near the binary-disk decoupling radius. We compare (surface) density profiles, accretion rates (relative to a single, non-spinning black hole), variability, and luminosities as functions of the mass ratio. We treat the disks in two limiting regimes: rapid radiative cooling and no radiative cooling. The magnetic field lines clearly reveal jets emerging from both black hole horizons and merging into one common jet at large distances. The magnetic fields give rise to much stronger shock heating than the pure hydrodynamic flows, completely alter the disk structure, and boost accretion rates and luminosities. Accretion streams near the horizons are among the densest structures; in fact, the 1:10 no-cooling evolution results in a refilling of the cavity. The typical effective temperature in the disk is $\sim 10^5 (M/10^8 M_\odot)^{-1/4} (L/L_{\rm edd})^{1/4} {\rm K}$ yielding characteristic thermal frequencies $\sim 10^{15}(M/10^8 M_\odot)^{-1/4} (L/L_{\rm edd})^{1/4}(1+z)^{-1}{\rm Hz}$. These systems are thus promising targets for extragalactic optical surveys, such as LSST, WFIRST, and PanSTARRS. [Preview Abstract] |
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