Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session H10: Sources of Gravitational Radiation |
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Sponsoring Units: GGR Chair: Carlos Lousto, University of Texas, Brownsville Room: Marriott Tampa Waterside Room 6 |
Sunday, April 17, 2005 8:30AM - 8:42AM |
H10.00001: How big a bump can you make on a neutron star? Benjamin Owen I estimate maximum elastic deformations for compact stars with exotic equations of state. Solid strange stars could sustain maximum ellipticities of $5\times10^{-5}$ rather than $6\times10^{-8}$ for conventional neutron stars, and hybrid stars could sustain $1\times10^{-6}$. Most of the difference is due to the shear modulus, which can be up to $10^{33}$~erg/cm$^3$ rather than $10^{30}$~erg/cm$^3$ in the inner crust of a conventional neutron star. Maximum solid strange star ellipticities are comparable to upper limits obtained for several known pulsars in a recent gravitational wave search by LIGO. Maximum ellipticities from the more robust hybrid model are on the edge of detectability by LIGO at initial design sensitivity for the same pulsars. A large shear modulus also strengthens the case for starquakes as an explanation for frequent pulsar glitches. [Preview Abstract] |
Sunday, April 17, 2005 8:42AM - 8:54AM |
H10.00002: Gravitomagnetic Love numbers and neutron star stability Marc Favata It is well known that a fluid star placed in a Newtonian tidal field will develop a mass quadrupole moment. The size of this induced mass quadrupole depends on the strength of the tidal field and the star's `Love number', a constant which depends on the equation of state. Similarly, a gravitomagnetic tidal field will induce a current quadrupole moment whose magnitude is proportional to the gravitomagnetic tidal field and the star's `gravitomagnetic Love number'. I will discuss the computation of this induced current quadrupole for rotating and non-rotating stars interacting with static and rotating tidal fields, as well as its application to neutron star binaries. In particular, the nonlinear interaction between the current quadrupole and gravitomagnetic field tends to increase the star's central density (although in most situations this effect is smaller than the well known stabilizing effect of a Newtonian tidal field). The induced current quadrupole vanishes for binaries that are corotating or irrotational, assumptions that are made in most numerical simulations of binary neutron stars. [Preview Abstract] |
Sunday, April 17, 2005 8:54AM - 9:06AM |
H10.00003: Diagnosing low $T/W$ dynamical instabilities in differentially rotating stars Shin'ichirou Yoshida, Motoyuki Saijo We investigate dynamical instabilities appearing in differentially rotating stars with rather low value of $T/|W|$ parameter (a ratio of rotational to gravitational energy), by using numerical non-linear hydrodynamics and linear eigenmode analysis. Particular attention are paid to the one-armed spiral instability and low $T/|W|$ bar instability, both of which are found recently \footnote {Centrella et al., 2001, ApJL, 550, 193 ; Saijo et al., 2003, ApJ, 595, 352; Shibata et al., 2002, MNRAS, 334, 27 } and are very interesting channels of possible gravitational radiation from rotating neutron stars. The nature of the dynamical instabilities is studied by using the canonical angular momentum \footnote{Friedman \& Schutz, 1978, ApJ, 221, 937} as a diagnostics. We find that the canonical angular momentum change its sign around the corotation radius and the instability grows through the interaction between inside and outside the corotation radius. This is in clear contrast with that of the classical dynamical instability without corotations, whose distribution of canonical angular momentum shows no feature. [Preview Abstract] |
Sunday, April 17, 2005 9:06AM - 9:18AM |
H10.00004: Astrophysical constraints on EMRIs Shane L. Larson Gravitational waves from the extreme mass ratio inspiral (EMRI) of stellar mass objects into supermassive black holes are an important prospective source in the LISA band. Orbits around the black hole which have small pericenter distances can exhibit non-Keplerian trajectories. In particular ``zoom-whirl'' orbits can cover multiple azimuthal periods for each radial period in the orbit, and produce interesting gravitational wave signals. This talk will examine the EMRI event rate and the importance of ``zoom-whirl'' orbits by coupling dynamical N-body simulations of stellar clusters with a semi-relativistic treatment of the orbits when they are near the black hole. [Preview Abstract] |
Sunday, April 17, 2005 9:18AM - 9:30AM |
H10.00005: Self force on a static scalar charge in Schwarzschild spacetime Swapnil Tripathi, Alan Wiseman, Tobias Keidl, John Friedman The finite part of the self force on a static scalar charge in a Schwarzschild spacetime vanishes [1]. It is recalculated here using a mode-by-mode expansion of the Green’s function. The Quinn-Wald axioms [2,3] have been used to regularize the self force. The motivation for this calculation is to develop techniques and formalism for use in calculations of the self forces (dissipative and conservative) acting on charges and masses moving in black hole spacetimes. \begin{thebibliography}{99} \bibitem{wiseman} A.G. Wiseman, Phys. Rev. D61 (2000) 084014 \bibitem{quinn}T.C. Quinn, Phys. Rev. D62 (2000) 064029 \bibitem{quinn-wald}T.C. Quinn, R.M. Wald Phys. Rev. D56 (1997) 3381 \end{thebibliography} [Preview Abstract] |
Sunday, April 17, 2005 9:30AM - 9:42AM |
H10.00006: Post-Minkowski action for point-particles and a helically symmetric binary solution John Friedman, Koji Uryu A Fokker action and equations of motion are obtained for two point particles in a post-Minkowski framework, in which the field of each particle is given by the half-retarded + half- advanced solution to the linearized Einstein equations. Expressions for the conserved four-momentum and the angular momentum tensor are obtained in terms of the particles' trajectories in this post-Minkowski approximation. A formal solution to the equations of motion is found for a binary system with circular orbits, the analog of a solution found independently by Schonberg and by Schild in the electromagnetic case. For a bound system of this kind, the post-Minkowski solution is a toy model that omits nonlinear terms of relevant post-Newtonian order; by adding to the action a post-Newtonian correction term, one obtains an innermost stable circular orbit. [Preview Abstract] |
Sunday, April 17, 2005 9:42AM - 9:54AM |
H10.00007: Computing self-forces with the Quinn-Wald axioms Alan G. Wiseman, John L. Friedman, Tobias S. Keidl, Swapnil Tripathi, Samuel Gralla A number of formal techniques have been developed for calculating the self-force, or radiation-reaction force, on small charges and masses moving in curved spacetimes. The difficulty has been putting these techniques to practical use in order to find the trajectory of falling charges (or masses) in a black hole spacetime. I will show how one of the formal techniques, the Quinn-Wald Axioms [1,2], can be used in practical calculations. [1] T.C. Quinn, Phys. Rev. D62 (2000) 064029 [2] T.C. Quinn, R.M. Wald Phys.Rev. D56 (1997) 3381 [Preview Abstract] |
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