Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session Y12: Gravitational Waves Sources and Phenomenology |
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Sponsoring Units: GGR Chair: Scott A. Hughes, Massachusetts Institute of Technology Room: Hyatt Regency Jacksonville Riverfront City Terrace 8 |
Tuesday, April 17, 2007 1:30PM - 1:42PM |
Y12.00001: Einstein@Home's search for spinning neutron stars Benjamin Owen Einstein@Home is both an APS outreach project and a LIGO science project: Users all over the world download a screensaver to search LIGO data for gravitational waves. In the past year (the second year of the project), users have searched data from S4 (LIGO's fourth science run) and are now searching S5, the first run at LIGO's full design sensitivity. We describe the methods and the status of these searches of the whole sky for spinning neutron stars. [Preview Abstract] |
Tuesday, April 17, 2007 1:42PM - 1:54PM |
Y12.00002: Taking measure of the Galaxy in low frequency gravitational waves Shane L. Larson, Brett Taylor, Matthew Benacquista The galaxy is populated with millions of compact binary star systems that radiate strongly in the low frequency gravitational wave band from 10 microHertz to 100 milliHertz. Spaceborne gravitational wave detectors will detect three distinct groups of stars within this population: a confusion foreground of unresolved stars, a group of stars which are essentially monochromatic in gravitational wave frequency during the observations, and a group of stars which have detectable frequency evolution (i.e. changing orbital periods) during the observations. This talk will discuss the use of several population synthesis realizations of the Milky Way galaxy to explore selection biases in gravitational wave data streams, and how these three distinct populations can be used to determine the bulk structure and shape of the Galaxy. [Preview Abstract] |
Tuesday, April 17, 2007 1:54PM - 2:06PM |
Y12.00003: Motion of a scalar charge around a Schwarzschild black hole Ian Vega We report on recent progress made towards the implementation of a fully-consistent, time-domain simulation of the motion of a scalar charge around a Schwarzschild black hole. Scalar charge dynamics in a curved background is influenced by the backreaction of scalar radiation on the charge producing it. This makes the calculation of the self-force a prerequisite to any consistent evolution code. A recently found decomposition of the Green's function for the scalar wave equation, in principle, affords us the capability of calculating this scalar self-force in time-domain, as opposed to mode-sum regularization schemes implemented in the frequency-domain. In this talk, we outline this alternative method and, as a check, examine its practicability for the simple case of circular orbits around Schwarzschild, for which reliable frequency-domain calculations exist and may be used for comparison. [Preview Abstract] |
Tuesday, April 17, 2007 2:06PM - 2:18PM |
Y12.00004: Radiation reaction force on a particle in Schwarzschild spacetime Swapnil Tripathi, Alan Wiseman The mathematical modelling of the radiation reaction force experienced by a particle in curved spacetime is very important for calculations of the templates used in detection of gravitational waves with LIGO, LISA etc. In particular, extreme mass ratio inspirals are strong candidates for gravitational wave detection with LISA. We model these systems as a particle in Schwarzschild spacetime, and use the Quinn Wald axioms to regularize the self force. Mode by mode expansion techniques are used for calculating the selfforce. Recent progress in this work is being reported in this talk\footnote{A.\ G.\ Wiseman, Phys. Rev. D {\bf 61} (2000) arXiv.org:gr-qc/084014} \footnote{T.C. Quinn, Phys. Rev. D {\bf 62} (2000) arXiv.org:gr- qc/064029} \footnote{T.C. Quinn, R.M. Wald Phys. Rev. D {\bf 56} (1997) 3381} [Preview Abstract] |
Tuesday, April 17, 2007 2:18PM - 2:30PM |
Y12.00005: Nonlinear development of the r-mode instability of accreting neutron stars: Three Modes Ruxandra Bondarescu, Saul Teukolsky, Ira Wasserman Rotating neutron stars have modes that are driven unstable by gravitational radiation reaction, principally the ``R-mode", a L=m=2 Rossby wave. It has been suggested that the R-mode instability is what sets the largest spin frequency of accreting neutron stars. This maximum frequency depends on the neutron star composition via viscous dissipation and neutrino cooling, and so is a probe of the high density nuclear physics of neutron stars. The nonlinear development of the instability plays a very important role in determining how this process works, and also illustrates how instabilities can saturate at low amplitudes as a consequence of nearly resonant excitation of other modes. We model the nonlinear effects using a minimal model, which includes three modes: the r-mode and the first two near-resonant modes it couples to that become unstable. We solve the coupled equations for the three-mode amplitudes in conjuction with the spin and temperature evolution numerically. The mode amplitudes settle quickly into quasi-stationary states that depend weakly on angular velocity and temperature. Eventually, the system may reach an equilibrium or undergo a cyclic evolution, with an r-mode amplitude $\sim 10^{-5}$. Alternatively, it may runaway, in which case the r-mode amplitude grows large enough to excite more modes and the three-mode model becomes insufficent. [Preview Abstract] |
Tuesday, April 17, 2007 2:30PM - 2:42PM |
Y12.00006: Computer algebra and nonlinear iterations for the development of the Periodic Wave Approximation Napoleon Hernandez, Richard Price, Benjamin Bromley, Christopher Beetle The periodic wave approximation, explored in the past few years by different people around the world, has a promising future modeling the gravitational waves obtained by a helical symmetric problem in General Relativity. The existence of a helical Killing vector allows the reduction in the number of degrees of freedom in the problem from 4 to 3. This situation promises to model adequately the slow inspiraling process of two black holes. The numerical solution of this problem involves the implementation of the eigenspectral method developed by Price et al., The motivation on the present is to show the set of computational tools that had been implemented in Maple{\copyright} as an aid in the development of the solution for the full GR problem. To illustrate the utility of such tools, partial results will be shown, involving the solution of one component of the perturbation tensor in a second order post-Minkowski expansion. The results will include a comparison between the solutions obtained through a) a perturbative approach and b) a numerical solver approach (using Newton Raphson). Finally, a review of future work will be given, including future goals and extensions of the present work. [Preview Abstract] |
Tuesday, April 17, 2007 2:42PM - 2:54PM |
Y12.00007: On finding fields and self-force in a gauge appropriate to separable wave equations John Friedman, Tobias Keidl, Alan Wiseman Gravitational waves from the inspiral of a stellar-size black hole to a supermassive black hole can be accurately approximated by a point particle moving in a Kerr background. We report progress on finding the renormalized self-force from the Teukolsky equation. The method is related to the MiSaTaQuWa renormalization and to the Detweiler-Whiting construction of the singular field. It relies on the fact that the renormalized $\psi_0$ (or $\psi_4$) is a {\em sourcefree} solution to the Teukolsky equation; and, following Chrzanowski, Cohen and Kegeles, one can therefore reconstruct a nonsingular renormalized metric in a radiation gauge. \newline \newline References: \newline [1] T. S. Keidl, J.~L.~Friedman, and A.~G.~Wiseman, Phys. Rev. D., in press; gr-qc/0611072. \newline [2] Y.\ Mino, M.\ Sasaki, and T.\ Tanaka, Phys. Rev. D {\bf 55}, 3457 (1997); T.\ C.\ Quinn and R.\ M.\ Wald, Phys. Rev. D {\bf 56}, 3381 (1997); S.\ Detweiler and B.\ F.Whiting, Phys. Rev. D {\bf 67}, 024025 (2003). [Preview Abstract] |
Tuesday, April 17, 2007 2:54PM - 3:06PM |
Y12.00008: On finding fields and self-force in a gauge appropriate to separable wave equations II Tobias Keidl, John Friedman, Alan Wiseman, Eirini Messaritaki, Dong Hoon Kim Gravitational waves from the inspiral of a stellar-size black hole to a supermassive black hole can be accurately approximated by a point particle moving in a Kerr background. A procedure for finding the renormalized self-force from the Tuekolsky equation \footnote{Teukolsky, S. A., Astrophys. J., \textbf{185}, 635-647, (1973)} has been outlined in the separate talk and paper \footnote{T.~S.~Keidl, J.~L.~Friedman, A.~G.~Wiseman, Phys. Rev. D, in press; gr-qc0611072}. A singular metric has been computed in THZ coordinates \footnote{K.\ S.\ Thorne and J.\ B.\ Hartle, Phys. Rev. D {\bf 31}, 1815 (1985)} \footnote{X.-H.\ Zhang, Phys. Rev. D {\bf 34}, 991 (1986)} (locally inertial on a geodesic), and has a simple form. In this talk, we focus on carrying out the procedure using the lowest order piece of the singular metric in Schwarzschild coordinates. We compute a lowest order non-singular $\psi_0$ and analyze the non-singular metric that arises. [Preview Abstract] |
Tuesday, April 17, 2007 3:06PM - 3:18PM |
Y12.00009: Visualising Gravitational Wave Event Candidates with the Coherent Event Display Adam Mercer, Sergey Klimenko A worldwide network of gravitational-wave detectors is now operating with unprecedented sensitivity. It is, therefore, becoming increasingly important to visualise event candidates from search pipelines using these detector networks. The Coherent Event Display has been developed with the goal of providing a simple and easy to use tool for performing follow up analyses of burst gravitational-wave event candidates. In this talk we discuss the implementation of the Coherent Event Display, its current status, and present examples from analysis of simulated signals and of detector noise fluctuations. [Preview Abstract] |
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