Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session G12: Gravitational Astrophysics |
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Sponsoring Units: GGR Chair: Carlos Lousto, Rochester Institute of Technology Room: Royal CD |
Sunday, May 1, 2011 8:30AM - 8:42AM |
G12.00001: Dynamics and Gravitational Wave Signature of Collapsar Formation Christian D. Ott, Christian Reisswig, Erik Schnetter, Evan O'Connor, Ulrich Sperhake, Frank Loeffler, Peter Diener, Ernazar Abdikamalov, Ian Hawke, Adam Burrows We present results from 3+1 general relativistic simulations of rotating core collapse in the context of the collapsar model for long gamma-ray bursts. We employ a realistic progenitor, rotation based on results of stellar evolution calculations, and a simplified equation of state. Our simulations track self-consistently collapse, bounce, the postbounce phase, black hole formation, and the subsequent early hyperaccretion phase. We extract gravitational waves from the spacetime curvature and identify a unique gravitational wave signature associated with the early phase of collapsar formation. [Preview Abstract] |
Sunday, May 1, 2011 8:42AM - 8:54AM |
G12.00002: ABSTRACT WITHDRAWN |
Sunday, May 1, 2011 8:54AM - 9:06AM |
G12.00003: Testing the black hole no-hair theorem at the galactic center Laleh Sadeghian, Clifford M. Will Precessions of the orbital planes of stars orbiting the galactic centre black hole depend only on the angular momentum and quadrupole moment of the central black hole. Therefore, studying precessions of the orbital planes of several stars can provide a way to test the black hole no-hair theorem, which requires that $Q=-J^2/M$. Such a measurement would give conclusive evidence that the galactic center object is really a black hole [1]. We are studying other factors that might perturb these orbits, including gravitational interaction with a population of other stars orbiting the GCBH. Using standard orbital perturbation theory, we have calculated analytically the time averaged rates of change of all the orbit elements of the target star caused by a given perturbing star and also, the r.m.s orbital plane precessions due to a population of perturbing stars inside and outside the orbit of the target star. We compare the results with those from numerical simulations [2]. Supported in part by the NSF, PHY 06-52448 and 09-65133. \\[4pt] [1] C. M. Will, Astrophys. J. Lett. 674, L25 (2008)\\[0pt] [2] D. Merritt et al., Phys. Rev. D 81, 062002 (2010) [Preview Abstract] |
Sunday, May 1, 2011 9:06AM - 9:18AM |
G12.00004: Astrometric Effects of a Stochastic Gravitational Wave Background Laura Book, Eanna Flanagan A stochastic gravitational wave background causes the apparent positions of distant sources to fluctuate, with angular deflections of order the characteristic strain amplitude of the gravitational waves. These fluctuations may be detectable with high precision astrometry, as first suggested by Braginsky et al. in 1990. In this talk I will present our results for the expected statistical properties of such an astrometric signal caused by a stochastic gravitational wave background, as well as the prospects for detecting it using next-generation astrometric surveys. [Preview Abstract] |
Sunday, May 1, 2011 9:18AM - 9:30AM |
G12.00005: Can Lensing Constrain a Boson Star in the Galactic Center Amitai Bin-Nun Over the last few decades, it has been increasingly clear that there is an extremely compact object at Sgr A* in the center of the galaxy. Some have looked at the theoretical gravitational lensing properties of this object, particularly on stars orbiting the galactic center. In this talk, I explore the possibility that a ``boson star'' or compact collection of scalar particles, is responsible for the large mass at Sgr A*. This possibility cannot be ruled out by observation of dynamical processes because of the compactness of a boson star. However, I argue that the gravitational lensing properties of a boson star have unique properties and their presence or absence would be very strong evidence for or against a boson star in the galactic center. [Preview Abstract] |
Sunday, May 1, 2011 9:30AM - 9:42AM |
G12.00006: Conformal Gravity Rotation Curves and the Impact of a Quadratic Potential in Conformal Gravity James O'Brien The use of Galactic Rotation Curves has long been thought to provide evidence for the existence of Dark Matter. Among the alternative theories to Dark Matter Gravitation, the Conformal Gravity theory first presented by Weyl and recently advanced by Mannheim and Kazanas presents a renormalizable, fourth order theory, which does not assume the existence of dark matter, nor is inferred as an ad hoc addition to standard gravity. Moreover, Conformal Gravity can serve to define the rotation curves of spiral and dwarf galaxies with no external free parameters, thus eliminating the ambiguity of the current dark matter halo mass models. We first present a recent modification to the Conformal Gravity potential, one which is of a scale much larger than the size of standard galaxies, and discuss its impact. We then present 110 rotation curves to Conformal Gravity, and show that the theory provides striking results, without preference to any particular choice of size or shape of galaxy. The un-biased sample includes galaxies of large spirals, dwarfs, irregulars, HSB's and LSB's, and in each and every case provides a rotation curve that is not only parameter free, but captures the structure of the data. [Preview Abstract] |
Sunday, May 1, 2011 9:42AM - 9:54AM |
G12.00007: How well can LISA measure black hole binaries when the spins are aligned by gas accretion? Ryan Lang, Scott Hughes, Neil Cornish Massive black hole binaries are one of the primary sources for the Laser Interferometer Space Antenna (LISA). The gravitational waves (GWs) measured by LISA will contain information about many properties of the binary, including masses, spins, sky location, and distance. We present results for how well LISA can measure these parameters. Spin precession effects are known to break degeneracies and consequently reduce parameter errors. However, gaseous torques may partially align the spins of a binary with its orbital angular momentum, suppressing the precession and severely degrading measurement. We show that including higher harmonics beyond the quadrupole can make up for this degradation. Like precession, higher harmonics break degeneracies and reduce errors; unlike precession, they are always present in the waveform, regardless of spin angle. When harmonics are included, parameters of partially aligned binaries are often measured as well or better than parameters of binaries with random spins but no harmonics. [Preview Abstract] |
Sunday, May 1, 2011 9:54AM - 10:06AM |
G12.00008: Apsidal Precession in Double White Dwarfs Binaries Francesca Valsecchi, Will Farr, Bart Willems, Christopher Deloye, Vassiliki Kalogera Galactic double white dwarfs (DWD) in close orbits are guaranteed gravitational wave (GW) sources for the Laser Interferometer Space Antenna (LISA) detector, with more than $10^4$ binaries expected to be detected over the mission's lifetime. Although the majority of them are expected to be circular, dynamical interactions in globular clusters can lead to a sub-population of detectable eccentric DWDs. Here we investigate the potential for probing white dwarf (WD) interiors through apsidal precession in eccentric binaries. For the first time, we analyze the tidal, rotational, and general relativistic (GR) contributions to this process using detailed WD models. We find that apsidal motion can lead to a detectable shift in the emitted GW signal; the effect is stronger for binaries with hot (young) WDs, and weaker for cool (old) WDs. Apsidal motion in cool DWDs is dominated by tides at orbital frequencies above $\sim$10$^{-3}$\,Hz ($10^{-4}$\,Hz for hot WDs). Therefore, only accounting for GR would inevitably lead to a bias in the mass measurements of these GW sources. Furthermore, we find that tidally-induced apsidal precession can be used as a unique probe of WD interiors. [Preview Abstract] |
Sunday, May 1, 2011 10:06AM - 10:18AM |
G12.00009: The Signature of Black Hole-Neutron Star Binaries Steven Liebling, Matthew Anderson, Eric Hirschmann, Luis Lehner, Patrick Motl, David Neilsen, Carlos Palenzuela Black hole-neutron star (BHNS) binaries are key gravitational wave sources, merging in the frequency band to which Earth-based GW detectors are most sensitive. Furthermore, as possible candidates for short-hard gamma ray bursts, combined observations in both gravitational and electromagnetic bands of BHNS mergers is thus an exciting possibility. This talk will discuss results from simulations that account for gravitational and magnetic effects as well as connections with processes capable of explaining key features of gamma ray bursts. [Preview Abstract] |
Sunday, May 1, 2011 10:18AM - 10:30AM |
G12.00010: Fully Nonlinear Numerical Evolutions of Small-Mass-Ratio Black-Hole Binaries Yosef Zlochower, Carlos Lousto, Manuela Campanelli, Hiroyuki Nakano In this talk we present results from the first fully nonlinear numerical simulations of black-hole binaries with mass ratios of 1:100. These simulations are based on the moving puncture formalism with a modified gauge condition and an optimal choice of the mesh refinement. The evolutions start with a small nonspinning black hole just outside the ISCO that orbits twice before plunging. We compute the gravitational radiation, as well as the final remnant parameters, and find close agreement with perturbative estimates. [Preview Abstract] |
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