[1110.4442] Effects of hyperons in binary neutron star mergers

Authors: Yuichiro Sekiguchi, Kenta Kiuchi, Koutarou Kyutoku, Masaru Shibata

Date: 20 Oct 2011

Abstract: Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling for the first time. It is found that even for the hyperonic EOS, a hypermassive neutron star is first formed after the merger for the typical total mass $\approx$ 2.7M\bigodot, and subsequently collapses to a black hole (BH). It is shown that hyperons play a substantial role in the post-merger dynamics, torus formation around the BH, and emission of gravitational waves (GWs). In particular, the existence of hyperons is imprinted in GWs. Therefore, GW observations will provide a potential opportunity to explore the composition of the neutron star matter.

abs pdf

Oct 31, 2011

1110.4442 (/preprints)
2011-10-31, 15:45 [edit]


[1110.4423] Relativistic Binaries in Globular Clusters

Authors: Matthew J. Benacquista, Jonathan M. B. Downing

Date: 20 Oct 2011

Abstract: Galactic globular clusters are old, dense star systems typically containing 10\super{4}--10\super{7} stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of hard binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct {\it N}-body integrations and Fokker--Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

abs pdf

Oct 31, 2011

1110.4423 (/preprints)
2011-10-31, 15:45 [edit]


[1110.5107] Multiple physical elements to determine the gravitational-wave signatures of core-collapse supernovae

Authors: Kei Kotake

Date: 24 Oct 2011

Abstract: We review recent progress in the theoretical predictions of gravitational waves (GWs) of core-collapse supernovae. Following a brief summary of the methods in the numerical modeling, we summarize multiple physical elements that determine the GW signatures which have been considered to be important in extracting the information of the long-veiled explosion mechanism from the observation of the GWs. We conclude with a summary of the most urgent tasks to make the dream come true.

abs pdf

Oct 31, 2011

1110.5107 (/preprints)
2011-10-31, 15:44 [edit]


[1110.5329] Slowly-rotating stars and black holes in dynamical Chern-Simons gravity

Authors: Yacine Ali-Haïmoud, Yanbei Chen

Date: 24 Oct 2011

Abstract: Chern-Simons (CS) modified gravity is an extension to general relativity (GR) in which the metric is coupled to a scalar field, resulting in modified Einstein field equations. In the dynamical theory, the scalar field is itself sourced by the Pontryagin density of the space-time. In this paper, the coupled system of equations for the metric and the scalar field is solved numerically for slowly-rotating neutron stars described with realistic equations of state and for slowly-rotating black holes. An analytic solution for a constant-density nonrelativistic object is also presented. It is shown that the black hole solution cannot be used to describe the exterior spacetime of a star as was previously assumed. In addition, whereas previous analysis were limited to the small-coupling regime, this paper considers arbitrarily large coupling strengths. It is found that the CS modification leads to two effects on the gravitomagnetic sector of the metric: (i) Near the surface of a star or the horizon of a black hole, the magnitude of the gravitomagnetic potential is decreased and frame-dragging effects are reduced in comparison to GR. (ii) In the case of a star, the angular momentum J, as measured by distant observers, is enhanced in CS gravity as compared to standard GR. For a large coupling strength, the near-zone frame-dragging effects become significantly screened, whereas the far-zone enhancement saturate at a maximum value max(Delta J) ~ (M/R) J. Using measurements of frame-dragging effects around the Earth by Gravity Probe B and the LAGEOS satellites, a weak but robust constraint is set to the characteristic CS lengthscale, xiˆ{¼} <~ 10ˆ8 km.

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Oct 31, 2011

1110.5329 (/preprints)
2011-10-31, 15:43 [edit]


[1110.5048] TeVeS/MOND is in harmony with gravitational redshifts in galaxy clusters

Authors: Jacob D. Bekenstein, Robert H. Sanders

Date: 23 Oct 2011

Abstract: Wojtak, Hansen and Hjorth have recently claimed to confirm general relativity and to rule out the tensor-vector-scalar (TeVeS) gravitational theory based on an analysis of the gravitational redshifts of galaxies in 7800 clusters. But their ubiquitous modeling of the sources of cluster gravitational fields with Navarro-Frenk-White mass profiles is neither empirically justified out to the necessary radii in clusters, nor germane in the case of TeVeS. Using MONDian isothermal sphere models consistently constructed within MOND (equivalent to TeVeS models), we can fit the determined redshifts no worse than does general relativity with dark halos. Wojtak, Hansen and Hjorth's work is further marred by confusion between the primitive mu-function of TeVeS and the MOND interpolation function.

abs pdf

Oct 31, 2011

1110.5048 (/preprints)
2011-10-31, 15:43 [edit]


[1110.6086] Pairing and sinking of binary SMBHs in sub-pc resolution simulations of galaxy mergers

Authors: Damien Chapon, Lucio Mayer, Romain Teyssier

Date: 27 Oct 2011

Abstract: We study the formation of a supermassive black hole (SMBH) binary and the shrinking of the separation of the two holes to sub-pc scales starting from a realistic major merger between two gas-rich spiral galaxies with mass comparable to our Milky Way. The simulations are the first of this kind carried out with an Adaptive Mesh refinement (AMR) code (here RAMSES), and the first capable to resolve separations as small as 0.1 pc. The collision of the two galaxies produces a gravo-turbulent rotating nuclear disk with mass (\sim 10ˆ9 Msun) and size (\sim 60 pc) in excellent agreement with previous SPH simulations with particle splitting that used a similar setup (Mayer et al. 2007) but were limited to separations of a few parsecs. The AMR results confirm that the two black holes sink rapidly as a result of dynamical friction onto the gaseous background, reaching a separation of 1 pc in less than 10ˆ7 yr. We show that the dynamical friction wake is well resolved by our model and we find good agreement with analytical predictions of the drag force as a function of the Mach number. Below 1 pc, black hole pairing slows down significantly, as the relative velocity between the sinking SMBH becomes highly subsonic and the mass contained within their orbit falls below the mass of the binary itself, rendering dynamical friction ineffective. Non-axisymmetric gas torques do not arise to restart sinking in absence of efficient dynamical friction, at variance with previous calculations using idealized equilibrium nuclear disk models. We believe that the rather "hot" EOS we used to model the multiphase turbulent ISM in the nuclear region is playing an important role in preventing efficient SMBH sinking inside the central parsec. We conclude with a discussion of the way forward to address sinking in gaseous backgrounds at sub-pc scales approaching the gravitational wave regime.

abs pdf

Oct 31, 2011

1110.6086 (/preprints)
2011-10-31, 15:41 [edit]


[1110.6172] Mapping the Galactic Center with Gravitational Wave measurements using Pulsar Timing

Authors: Bence Kocsis, Alak Ray, Simon Portegies Zwart

Date: 27 Oct 2011

Abstract: We examine the nHz gravitational wave (GW) foreground of stars and black holes (BHs) orbiting SgrA* in the Galactic Center. A cusp of stars and BHs generates a continuous GW spectrum below 40 nHz; individual BHs within 1 mpc to SgrA* stick out in the spectrum at higher GW frequencies. The GWs and gravitational near-field effects can be resolved by timing pulsars within a few pc of this region. Observations with the Square Kilometer Array (SKA) may be especially sensitive to intermediate mass black holes (IMBHs) in this region, if present. A 100ns-10mus timing accuracy is sufficient to detect BHs of mass 1000 Msun with pulsars at distance 0.1-1 pc in a 3 yr observation baseline. Unlike electromagnetic imaging techniques, the prospects for resolving individual objects through GW measurements improve closer to SgrA*, even if the number density of objects increases inwards steeply. Scattering by the interstellar medium will pose the biggest challenge for such observations.

abs pdf

Oct 31, 2011

1110.6172 (/preprints)
2011-10-31, 15:40 [edit]


[1110.5950] Post-Newtonian, Quasi-Circular Binary Inspirals in Quadratic Modified Gravity

Authors: Kent Yagi, Leo C. Stein, Nicolas Yunes, Takahiro Tanaka

Date: 27 Oct 2011

Abstract: We consider a general class of quantum gravity-inspired, modified gravity theories, where the Einstein-Hilbert action is extended through the addition of all terms quadratic in the curvature tensor coupled to scalar fields with standard kinetic energy. This class of theories includes Einstein-Dilaton-Gauss-Bonnet and Chern-Simons modified gravity as special cases. We analytically derive and solve the coupled field equations in the post-Newtonian approximation, assuming a comparable-mass, spinning black hole binary source in a quasi-circular, weak-field/slow-motion orbit. We find that a naive subtraction of divergent piece associated with the point-particle approximation is ill-suited to represent compact objects in these theories. Instead, we model them by appropriate effective sources built so that known strong-field solutions are reproduced in the far-field limit. In doing so, we prove that black holes in Einstein-Dilaton-Gauss-Bonnet and Chern-Simons theory can have hair, while neutron stars have no scalar monopole charge, in diametrical opposition to results in scalar-tensor theories. We then employ techniques similar to the direct integration of the relaxed Einstein equations to obtain analytic expressions for the scalar field, metric perturbation, and the associated gravitational wave luminosity measured at infinity. We find that scalar field emission mainly dominates the energy flux budget, sourcing electric-type (even-parity) dipole scalar radiation and magnetic-type (odd-parity) quadrupole scalar radiation, correcting the General Relativistic prediction at relative -1PN and 2PN orders. Such modifications lead to corrections in the emitted gravitational waves that can be mapped to the parameterized post-Einsteinian framework. Such modifications could be strongly constrained with gravitational wave observations.

abs pdf

Oct 28, 2011

1110.5950 (/preprints)
2011-10-28, 21:37 [edit]


[1110.4169] Prospects for determination of thermal history after inflation with future gravitational wave detectors

Authors: Sachiko Kuroyanagi, Kazunori Nakayama, Shun Saito

Date: 19 Oct 2011

Abstract: Thermal history of the Universe between inflation and big-bang nucleosynthesis has not yet been revealed observationally. It will be probed by the detection of primordial gravitational waves generated during inflation, which contain information on the reheating temperature as well as the equation of state of the Universe after inflation. Based on Fisher information formalism, we examine how accurately the tensor-to-scalar ratio and reheating temperature after inflation can be simultaneously determined with space-based gravitational wave detectors such as the DECI-hertz Interferometer Gravitational-wave Observatory (DECIGO) and the Big-Bang Observer (BBO). We show that the reheating temperature is best determined if it is around 10ˆ7 GeV for tensor-to-scalar ratio of around 0.1, and explore the detectable parameter space. We also find that equation of state of the early Universe can be also determined accurately enough to distinguish different equation-of-state parameters if the inflationary gravitational waves are successfully detected. Thus future gravitational wave detectors provide a unique and promising opportunity to reveal the thermal history of the Universe around 10ˆ7 GeV.

abs pdf

Oct 20, 2011

1110.4169 (/preprints)
2011-10-20, 12:40 [edit]


[1110.3764] Black hole stereotyping: Induced gravito-static polarization

Authors: Barak Kol, Michael Smolkin

Date: 17 Oct 2011

Abstract: We discuss the black hole effective action and define its static subsector. We determine the induced gravito-static polarization constants (electric Love numbers) of static black holes (Schwarzschild) in an arbitrary dimension, namely the induced mass multipole as a result of an external gravitational field. We demonstrate that in 4d these constants vanish thereby settling a disagreement in the literature. Yet in higher dimensions these constants are non-vanishing, thereby disproving (at least in d>4) speculations that black holes have no effective couplings beyond the point particle action. In particular, when l/(d-3) is half integral these constants demonstrate a (classical) renormalization flow consistent with the divergences of the effective field theory. In some other cases the constants are negative indicating a novel non-spherical instability.
The theory of hypergeometric functions plays a central role.

abs pdf

Oct 18, 2011

1110.3764 (/preprints)
2011-10-18, 16:25 [edit]


[1110.3759] Neutron star equation of state via gravitational wave observations

Authors: Charalampos Markakis, Jocelyn S. Read, Masaru Shibata, Koji Uryu, Jolien D. E. Creighton, John L. Friedman, Benjamin D. Lackey

Date: 17 Oct 2011

Abstract: Gravitational wave observations can potentially measure properties of neutron star equations of state by measuring departures from the point-particle limit of the gravitational waveform produced in the late inspiral of a neutron star binary. Numerical simulations of inspiraling neutron star binaries computed for equations of state with varying stiffness are compared. As the stars approach their final plunge and merger, the gravitational wave phase accumulates more rapidly if the neutron stars are more compact. This suggests that gravitational wave observations at frequencies around 1 kHz will be able to measure a compactness parameter and place stringent bounds on possible neutron star equations of state. Advanced laser interferometric gravitational wave observatories will be able to tune their frequency band to optimize sensitivity in the required frequency range to make sensitive measures of the late-inspiral phase of the coalescence.

abs pdf

Oct 18, 2011

1110.3759 (/preprints)
2011-10-18, 16:25 [edit]


[1110.3169] Searching for electromagnetic counterparts of gravitational wave transients

Authors: M. Branchesi (1,2)on behalf of the LIGO Scientific Collaboration, the Virgo Collaboration, A. Klotz (3), M. Laas-Bourez (4) ((1) Universit&#xe0; degli Studi di Urbino "Carlo Bo", Italy, (2) INFN - Sezione di Firenze, Italy, (3) Universit&#xe8; de Toulouse/IRAP, France, (4) ICRAR/School of Physics, University of Western Australia, Australia)

Date: 14 Oct 2011

Abstract: A pioneering electromagnetic (EM) observation follow-up program of candidate gravitational wave (GW) triggers has been performed, Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010, during the recent LIGO/Virgo run. The follow-up program involved ground-based and space EM facilities observing the sky at optical, X-ray and radio wavelengths. The joint GW/EM observation study requires the development of specific image analysis procedures able to discriminate the possible EM counterpart of GW trigger from background events. The paper shows an overview of the EM follow-up program and the developing image analysis procedures as they are applied to data collected with TAROT and Zadko.

abs pdf

Oct 17, 2011

1110.3169 (/preprints)
2011-10-17, 15:33 [edit]


[1110.3297] Loosely coherent searches for sets of well-modeled signals

Authors: Vladimir Dergachev

Date: 14 Oct 2011

Abstract: We introduce a high-performance implementation of a loosely coherent statistic sensitive to signals spanning a finite-dimensional manifold in parameter space. Results from full scale simulations on Gaussian noise are discussed, as well as implications for future searches for continuous gravitational waves. We demonstrate an improvement of more than an order of magnitude in analysis speed over previously available algorithms. As searches for continuous gravitational waves are computationally limited, the large speedup results in gain in sensitivity.

abs pdf

Oct 17, 2011

1110.3297 (/preprints)
2011-10-17, 15:33 [edit]


[1110.3193] Euclid Definition Study Report

Authors: Editorial Team: R. Laureijs, J. Amiaux, S. Arduini, J.-L. Augu&#xe8;res, J. Brinchmann, R. Cole, M. Cropper, C. Dabin, L. Duvet, A. Ealet, B. Garilli, P. Gondoin, L. Guzzo, J. Hoar, H. Hoekstra, R. Holmes, T. Kitching, T. Maciaszek, Y. Mellier, F. Pasian, W. Percival, J. Rhodes, G. Saavedra Criado, M. Sauvage, R. Scaramella, L. Valenziano, S. Warren

Date: 14 Oct 2011

Abstract: Euclid is a space-based survey mission from the European Space Agency designed to understand the origin of the Universe's accelerating expansion. It will use cosmological probes to investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of structure formation. The mission is optimised for two independent primary cosmological probes: Weak gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). The Euclid payload consists of a 1.2 m Korsch telescope designed to provide a large field of view. It carries two instruments with a common field-of-view of ~0.54 deg2: the visual imager (VIS) and the near infrared instrument (NISP) which contains a slitless spectrometer and a three bands photometer. The Euclid wide survey will cover 15,000 deg2 of the extragalactic sky and is complemented by two 20 deg2 deep fields. For WL, Euclid measures the shapes of 30-40 resolved galaxies per arcmin2 in one broad visible R+I+Z band (550-920 nm). The photometric redshifts for these galaxies reach a precision of dz/(1+z) < 0.05. They are derived from three additional Euclid NIR bands (Y, J, H in the range 0.92-2.0 micron), complemented by ground based photometry in visible bands derived from public data or through engaged collaborations. The BAO are determined from a spectroscopic survey with a redshift accuracy dz/(1+z) =0.001. The slitless spectrometer, with spectral resolution ~250, predominantly detects Ha emission line galaxies. Euclid is a Medium Class mission of the ESA Cosmic Vision 2015-2025 programme, with a foreseen launch date in 2019. This report (also known as the Euclid Red Book) describes the outcome of the Phase A study.

abs pdf

Oct 17, 2011

1110.3193 (/preprints)
2011-10-17, 15:33 [edit]


[1110.3081] Modeling multipolar gravitational-wave emission from small mass-ratio mergers

Authors: Enrico Barausse, Alessandra Buonanno, Scott A. Hughes, Gaurav Khanna, Stephen O&#x27;Sullivan, Yi Pan

Date: 13 Oct 2011

Abstract: Using the effective-one-body (EOB) formalism and a time-domain Teukolsky code, we generate inspiral, merger, and ringdown waveforms in the small mass-ratio limit. We use EOB inspiral and plunge trajectories to build the Teukolsky equation source term, and compute full coalescence waveforms for a range of black hole spins. By comparing EOB waveforms that were recently developed for comparable mass binary black holes to these Teukolsky waveforms, we improve the EOB model for the (2,2), (2,1), (3,3), and (4,4) modes. Our results can be used to quickly and accurately extract useful information about merger waves for binaries with spin, and should be useful for improving analytic models of such binaries. Although in this analysis we only consider equatorial inspirals (orbital angular momentum parallel to spin), there is no issue of principle preventing us from considering inclined binaries. We will extend this analysis to examine misaligned spin-orbit configurations in future work.

abs pdf

Oct 17, 2011

1110.3081 (/preprints)
2011-10-17, 15:33 [edit]


[1110.2865] Cosmology with space-based gravitational-wave detectors --- dark energy and primordial gravitational waves ---

Authors: Atsushi Nishizawa, Kent Yagi, Atsushi Taruya, Takahiro Tanaka

Date: 13 Oct 2011

Abstract: Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect ~10ˆ6 neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and be a unique probe for dark energy. On the other hand, such a NS-binary foreground should be subtracted to detect primordial GWs produced during inflation. Thus, the constraining power on dark energy and the detectability of the primordial gravitational waves strongly depend on the detector sensitivity and are in close relation with one another. In this paper, we investigate the constraints on the equation of state of dark energy with future space-based GW detectors with/without identifying the redshifts of host galaxies. We also study the sensitivity to the primordial GWs, properly dealing with the residual of the NS binary foreground. Based on the results, we discuss the detector sensitivity required to achieve the forementioned targeted study of cosmology.

abs pdf

Oct 14, 2011

1110.2865 (/preprints)
2011-10-14, 22:16 [edit]


[1110.2785] Multi-physics simulations using a hierarchical interchangeable software interface

Authors: Simon Portegies Zwart, Stephen McMillan, Inti Pelupessy, Arjen van Elteren

Date: 12 Oct 2011

Abstract: We introduce a general-purpose framework for interconnecting scientific simulation programs using a homogeneous, unified software interface. Our framework is intrinsically parallel, and conveniently separates all components in memory. It performs unit conversion between different modules automatically and defines common data structures to communicate across different codes. We use the framework to simulate embedded star clusters. For this purpose we couple solvers for gravitational dynamics, stellar evolution and hydrodynamics to self consistently resolve the dynamical evolution simultaneousy with the internal nuclear evolution of the stars and the hydrodynamic response of the gas. We find, in contrast to earlier studies, that the survival of a young star cluster depends only weakly on the efficiency of star formation. The main reason for this weak dependency is the asymmetric expulsion of the embedding gas from the cluster.

abs pdf

Oct 14, 2011

1110.2785 (/preprints)
2011-10-14, 22:15 [edit]


[1110.2965] A geometric approach to the precession of compact binaries

Authors: Michael Boyle, Robert Owen, Harald P. Pfeiffer

Date: 13 Oct 2011

Abstract: We propose a geometrical method to define a preferred reference frame for precessing binary systems. This minimal-rotation frame is aligned with the angular-momentum axis and fixes the rotation about that axis up to a constant angle, resulting in an essentially invariant frame. Gravitational waveforms decomposed in this frame are similarly invariant under rotations of the inertial frame and exhibit relatively smoothly varying phase. By contrast, earlier prescriptions for radiation-aligned frames induce extraneous features in the gravitational-wave phase which depend on the orientation of the inertial frame, which leads to fluctuations in the frequency and may compound to many gravitational-wave cycles. We suggest that the minimal-rotation frame provides a simplified framework for post-Newtonian approximations of precessing systems and describe the construction of analytical/numerical hybrid waveforms for such systems.

abs pdf

Oct 14, 2011

1110.2965 (/preprints)
2011-10-14, 22:15 [edit]


[1110.2938] Energy versus Angular Momentum in Black Hole Binaries

Authors: Thibault Damour, Alessandro Nagar, Denis Pollney, Christian Reisswig

Date: 13 Oct 2011

Abstract: Using accurate numerical relativity simulations of (nonspinning) black-hole binaries with mass ratios 1:1, 2:1 and 3:1 we compute the gauge invariant relation between the (reduced) binding energy $E$ and the (reduced) angular momentum $j$ of the system. We show that the relation $E(j)$ is an accurate diagnostic of the dynamics of a black-hole binary in a highly relativistic regime. By comparing the numerical-relativity $Eˆ{\rm NR} (j)$ curve with the predictions of several analytic approximation schemes, we find that, while the usual, non-resummed post-Newtonian-expanded $Eˆ{\rm PN} (j)$ relation exhibits large and growing deviations from $Eˆ{\rm NR} (j)$, the prediction of the effective one-body formalism, based purely on known analytical results (without any calibration to numerical relativity), agrees strikingly well with the numerical-relativity results.

abs pdf

Oct 14, 2011

1110.2938 (/preprints)
2011-10-14, 22:15 [edit]


[1110.2720] Constraining Generic Lorentz Violation and the Speed of the Graviton with Gravitational Waves

Authors: Saeed Mirshekari, Nicolas Yunes, Clifford M. Will

Date: 12 Oct 2011

Abstract: Modified gravity theories generically predict a violation of Lorentz invariance, which may lead to a modified dispersion relation for propagating modes of gravitational waves. We construct a parametrized dispersion relation that can reproduce a range of known Lorentz-violating predictions and investigate their impact on the propagation of gravitational waves. A modified dispersion relation forces different wavelengths of the gravitational wave train to travel at slightly different velocities, leading to a modified phase evolution observed at a gravitational-wave detector. We show how such corrections map to the waveform observable and to the parametrized post-Einsteinian framework, proposed to model a range of deviations from General Relativity. Given a gravitational-wave detection, the lack of evidence for such corrections could then be used to place a constraint on Lorentz violation. The constraints we obtain are tightest for dispersion relations that scale with small power of the graviton's momentum and deteriorate for a steeper scaling.

abs pdf

Oct 13, 2011

1110.2720 (/preprints)
2011-10-13, 13:50 [edit]


[1110.2229] Accurate gravitational waveforms for binary-black-hole mergers with nearly extremal spins

Authors: Geoffrey Lovelace, Michael Boyle, Mark A. Scheel, Bela Szilagyi

Date: 10 Oct 2011

Abstract: Motivated by the possibility of observing gravitational waves from merging black holes whose spins are nearly extremal (i.e., 1 in dimensionless units), we present numerical waveforms from simulations of merging black holes with the highest spins simulated to date: (1) a 25.5-orbit inspiral, merger, and ringdown of two holes with equal masses and spins of magnitude 0.97 aligned with the orbital angular momentum; and (2) a previously reported 12.5-orbit inspiral, merger, and ringdown of two holes with equal masses and spins of magnitude 0.95 anti-aligned with the orbital angular momentum. First, we consider the horizon mass and spin evolution of the new aligned-spin simulation. During the inspiral, the horizon area and spin evolve in remarkably close agreement with Alvi's analytic predictions, and the remnant hole's final spin agrees reasonably well with several analytic predictions. We also find that the total energy emitted by a real astrophysical system with these parameters — almost all of which is radiated during the time included in this simulation — would be 10.952% of the initial mass at infinite separation. Second, we consider the gravitational waveforms for both simulations. After estimating their uncertainties, we compare the waveforms to several post-Newtonian approximants, finding significant disagreement well before merger, although the phase of the TaylorT4 approximant happens to agree remarkably well with the numerical prediction in the aligned-spin case. We find that the post-Newtonian waveforms have sufficient uncertainty that hybridized waveforms will require far longer numerical simulations (in the absence of improved post-Newtonian waveforms) for accurate parameter estimation of low-mass binary systems.

abs pdf

Oct 11, 2011

1110.2229 (/preprints)
2011-10-11, 22:23 [edit]


[1110.1635] Missing Black Holes Unveil The Supernova Explosion Mechanism

Authors: K. Belczynski, G. Wiktorowicz, C. Fryer, D. Holz, V. Kalogera

Date: 7 Oct 2011

Abstract: There exist a wide range of masses and types of stars that form compact object remnants: white dwarfs, neutron stars, or black holes. The stellar mass distribution is smooth, covering the range 0.1-100 Msun. It is expected that the masses of the ensuing compact remnants correlate with the masses of their progenitor stars, and thus it is thought that the remnant masses should be smoothly distributed from the lightest white dwarfs to the heaviest black holes. However, this intuitive prediction is not borne out by observed data. In the rapidly growing population of remnants with determined masses, a striking mass gap has emerged at the boundary between neutron stars and black holes. The heaviest neutron stars reach a maximum of 2 Msun, while the lightest black holes are at least 5 Msun. At first this gap was attributed to a paucity of observations. However, with recent determinations of the masses for more than 20 black holes, the gap has remained intact and become a significant challenge to our understanding of compact object formation. Over a decade after this gap was initially noted, we offer the first insights into the physical processes that bifurcate the formation of remnants into lower mass neutron stars and heavier black holes. Combining the results of full stellar modeling with multidimensional hydrodynamic simulations of supernova explosions, we both explain the existence of the gap, and also put stringent constraints on the inner workings of the supernova explosion mechanism. In particular, we show that core-collapse supernovae are launched within 100-200 ms of the initial stellar collapse. This implies that the explosions are driven by Rayleigh-Taylor instabilities rather than the delayed standing accretion shock instabilities, resolving a major debate in the supernova community.

abs pdf

Oct 11, 2011

1110.1635 (/preprints)
2011-10-11, 22:23 [edit]


[1110.2051] The microwave sky after one year of Planck operations

Authors: Aniello Mennella, for the Planck Collaboration

Date: 10 Oct 2011

Abstract: The ESA Planck satellite, launched on May 14th, 2009, is the third generation space mission dedicated to the measurement of the Cosmic Microwave Background (CMB), the first light in the Universe. Planck observes the full sky in nine frequency bands from 30 to 857 GHz and is designed to measure the CMB anisotropies with an unprecedented combination of sensitivity, angular resolution and control of systematic effects. In this presentation we summarise the Planck instruments performance and discuss the main scientific results obtained after one year of operations in the fields of galactic and extragalactic astrophysics.

abs pdf

Oct 11, 2011

1110.2051 (/preprints)
2011-10-11, 22:22 [edit]


[1110.2094] Elimination of the spin supplementary condition in the effective field theory approach to the post-Newtonian approximation

Authors: Steven Hergt, Jan Steinhoff, Gerhard Schaefer

Date: 10 Oct 2011

Abstract: The present paper addresses open questions regarding the handling of the spin supplementary condition within the effective field theory approach to the post-Newtonian approximation. In particular it is shown how the spin supplementary condition can be eliminated at the level of the potential and how the dynamics can be cast into a fully reduced Hamiltonian form. Two different methods are used and compared, one based on the well-known Dirac bracket and the other based on an action principle. It is discussed how the latter approach can be used to improve the Feynman rules by formulating them in terms of reduced canonical spin variables.

abs pdf

Oct 11, 2011

1110.2094 (/preprints)
2011-10-11, 22:22 [edit]


[1110.1668] On Toroidal Horizons in Binary Black Hole Inspirals

Authors: Michael I. Cohen, Jeffrey D. Kaplan, Mark A. Scheel

Date: 7 Oct 2011

Abstract: We examine the structure of the event horizon for numerical simulations of two black holes that begin in a quasicircular orbit, inspiral, and finally merge. We find that the spatial cross section of the merged event horizon has spherical topology (to the limit of our resolution), despite the expectation that generic binary black hole mergers in the absence of symmetries should result in an event horizon that briefly has a toroidal cross section. Using insight gained from our numerical simulations, we investigate how the choice of time slicing affects both the spatial cross section of the event horizon and the locus of points at which generators of the event horizon cross. To ensure the robustness of our conclusions, our results are checked at multiple numerical resolutions. 3D visualization data for these resolutions are available for public access online. We find that the structure of the horizon generators in our simulations is consistent with expectations, and the lack of toroidal horizons in our simulations is due to our choice of time slicing.

abs pdf

Oct 11, 2011

1110.1668 (/preprints)
2011-10-11, 22:22 [edit]


[1110.1099] A test of the (circular) Unruh effect using atoms

Authors: Navid Rad, Douglas Singleton

Date: 5 Oct 2011

Abstract: We propose a test for the (circular) Unruh effect using certain atoms -- fluorine and oxygen. For these atoms the centripetal acceleration of the outer shell electrons implies an effective Unruh temperature in the range 1000 - 2000 K. This range of Unruh temperatures is large enough to excite a significant fraction of the outer electrons into low lying energy levels above the ground state. Examining these atoms at low background temperatures and finding a larger than expected number of electrons in low lying excited states, beyond what is expected due to the background thermal excitation, would provide experimental evidence for the Unruh effect.

abs pdf

Oct 11, 2011

1110.1099 (/preprints)
2011-10-11, 22:22 [edit]


[1109.6660] Observing Lense-Thirring Precession in Tidal Disruption Flares

Authors: Nicholas Stone, Abraham Loeb

Date: 29 Sep 2011

Abstract: When a star is tidally disrupted by a supermassive black hole (SMBH), the streams of liberated gas form an accretion disk after their return to pericenter. We demonstrate that Lense-Thirring precession in the spacetime around a rotating SMBH can produce significant time evolution of the disk angular momentum vector, due to both the periodic precession of the disk and the nonperiodic, differential precession of the bound debris streams. Jet precession and periodic modulation of disk luminosity are possible consequences. The persistence of the jetted X-ray emission in the Swift J164449.3+573451 flare suggests that the jet axis was aligned with the spin axis of the SMBH during this event.

abs pdf

Oct 05, 2011

1109.6660 (/preprints)
2011-10-05, 18:54 [edit]


[1110.0746] Towards constraining the central black hole's properties by studying its infrared flares with the GRAVITY instrument

Authors: F. H. Vincent, T. Paumard, G. Perrin, E. Gourgoulhon, F. Eisenhauer, S. Gillessen

Date: 4 Oct 2011

Abstract: The ability of the near future second generation VLTI instrument GRAVITY to constrain the properties of the Galactic center black hole is investigated. The Galactic center infrared flares are used as probes of strong-field gravity, within the framework of the hot spot model according to which the flares are the signature of a blob of gas orbiting close to the black hole's innermost stable circular orbit. Full general relativistic computations are performed, together with realistic observed data simulations, that lead to conclude that GRAVITY could be able to constrain the black hole's inclination parameter.

abs pdf

Oct 05, 2011

1110.0746 (/preprints)
2011-10-05, 11:08 [edit]


[1110.0659] Testing Gravitation in the Solar System with Radio Science experiments

Authors: A. Hees, P. Wolf, B. Lamine, M.T. Jaekel, C. Le Poncin-Lafitte, V. Lainey, V. Dehant

Date: 4 Oct 2011

Abstract: The laws of gravitation have been tested for a long time with steadily improving precision, leading at some moment of time to paradigmatic evolutions. Pursuing this continual effort is of great importance for science. In this communication, we focus on Solar System tests of gravity and more precisely on possible tests that can be performed with radio science observations (Range and Doppler). After briefly reviewing the current tests of gravitation at Solar System scales, we give motivations to continue such experiments. In order to obtain signature and estimate the amplitude of anomalous signals that could show up in radio science observables because of modified gravitational laws, we developed a new software that simulates Range/Doppler signals. We present this new tool that simulates radio science observables directly from the space-time metric. We apply this tool to the Cassini mission during its cruise from Jupiter to Saturn and derive constraints on the parameters entering alternative theories of gravity beyond the standard Parametrized Post Newtonian theory.

abs pdf

Oct 05, 2011

1110.0659 (/preprints)
2011-10-05, 11:07 [edit]


[1110.0687] Can we constrain the maximum value for the spin parameter of the super-massive objects in galactic nuclei without knowing their actual nature?

Authors: Cosimo Bambi

Date: 4 Oct 2011

Abstract: In 4-dimensional General Relativity, black holes are described by the Kerr solution and are subject to the bound $|a_*| \le 1$, where $a_*$ is the black hole spin parameter. If current black hole candidates are not the black holes predicted in General Relativity, this bound does not hold and $a_*$ might exceed 1. In this letter, I relax the Kerr black hole hypothesis and I find that the value of the spin parameter of the super-massive black hole candidates in galactic nuclei cannot be higher than about 1.2. A higher spin parameter would not be consistent with a radiative efficiency $\eta > 0.15$, as observed at least for the most luminous AGN. While a rigorous proof is lacking, I conjecture that the bound $|a_*| \lesssim 1.2$ is independent of the exact nature of these objects.

abs pdf

Oct 05, 2011

1110.0687 (/preprints)
2011-10-05, 11:07 [edit]


[1110.0530] Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence

Authors: T. G. F. Li, W. Del Pozzo, S. Vitale, C. Van Den Broeck, M. Agathos, J. Veitch, K. Grover, T. Sidery, R. Sturani, A. Vecchio

Date: 3 Oct 2011

Abstract: Coalescences of binary neutron stars and/or black holes are amongst the most likely gravitational-wave signals to be observed in ground based interferometric detectors. Apart from the astrophysical importance of their detection, they will also provide us with our very first empirical access to the genuinely strong-field dynamics of General Relativity (GR). We present a Bayesian data analysis method aimed at detecting deviations from GR, through measuring the consistency of the gravitational-wave phase coefficients in the inspiral regime with the predictions made by GR, without relying on any specific alternative theory of gravity. Sources in the Advanced LIGO and Virgo detectors are likely to have low a signal-to-noise ratio (SNR). Therefore, here we introduce a framework in which individual sources are analysed for deviations in a limited number of the first few phase coefficients, which are the most easily determined in a low-SNR scenario. We also show that by combining the results of multiple observations one can achieve a more powerful test than for any individual source. In order to explore this problem, we perform a range of numerical experiments in which simulated gravitational waves modeled in the restricted post-Newtonian, stationary phase approximation are added to Gaussian and stationary noise that follows the expected Advanced LIGO/Virgo noise curves.

abs pdf

Oct 05, 2011

1110.0530 (/preprints)
2011-10-05, 11:06 [edit]


[1110.0410] The Electromagnetic Christodoulou Memory Effect and its Application to Neutron Star Binary Mergers

Authors: Lydia Bieri, PoNing Chen, Shing-Tung Yau

Date: 3 Oct 2011

Abstract: Gravitational waves are predicted by the general theory of relativity. It has been shown that gravitational waves have a nonlinear memory, displacing test masses permanently. This is called the Christodoulou memory. We proved that the electromagnetic field contributes at highest order to the nonlinear memory effect of gravitational waves, enlarging the permanent displacement of test masses. In experiments like LISA or LIGO which measure distances of test masses, the Christodoulou memory will manifest itself as a permanent displacement of these objects. It has been suggested to detect the Christodoulou memory effect using radio telescopes investigating small changes in pulsar's pulse arrival times. The latter experiments are based on present-day technology and measure changes in frequency. In the present paper, we study the electromagnetic Christodoulou memory effect and compute it for binary neutron star mergers. These are typical sources of gravitational radiation. During these processes, not only mass and momenta are radiated away in form of gravitational waves, but also very strong magnetic fields are produced and radiated away. Moreover, a large portion of the energy is carried away by neutrinos. We give constraints on the conditions, where the energy transported by electromagnetic radiation is of similar or slightly higher order than the energy radiated in gravitational waves or in form of neutrinos. We find that for coalescing neutron stars, large magnetic fields magnify the Christodoulou memory as long as the gaseous environment is sufficiently rarefied. Thus the observed effect on test masses of a laser interferometer gravitational wave detector will be enlarged by the contribution of the electromagnetic field. Therefore, the present results are important for the planned experiments.

abs pdf

Oct 04, 2011

1110.0410 (/preprints)
2011-10-04, 17:40 [edit]


[1110.0017] Empirical Constraints on the Coevolution of Supermassive Black Holes and their Host Spheroids

Authors: Gongjie Li, Charlie Conroy, Abraham Loeb

Date: 30 Sep 2011

Abstract: We investigate the evolution of the MBH-{\sigma} relation by examining the relationship between the intrinsic scatter in the MBH-{\sigma} relation and galaxy bolometric nuclear luminosity, the latter being a probe of the accretion rate of the black hole (BH). Our sample is composed of galaxies with classical bulges when possible, of which 38 have dynamically measured BHs masses, and 17 have BHs masses measured by reverberation mapping. In order to obtain the bolometric nuclear luminosity for galaxies with low nuclear luminosity, we convert the X-ray nuclear luminosity measured by Chandra to bolometric luminosity. We find that the scatter in the MBH-{\sigma} relation is uncorrelated with nuclear luminosity over seven orders of magnitude in luminosity, with the high luminosity end approaching the Eddington luminosity. This suggests that at the present epoch galaxies evolve along the MBH-{\sigma} relation. This conclusion is consistent with the standard paradigm that BHs grow contemporaneously with their host stellar spheroids.

abs pdf

Oct 04, 2011

1110.0017 (/preprints)
2011-10-04, 17:40 [edit]


[1110.0342] Measuring the absolute non-gravitational acceleration of a spacecraft: goals, devices, methods, performances

Authors: Benjamin Lenoir, Bruno Christophe, Serge Reynaud

Date: 3 Oct 2011

Abstract: Space provides unique opportunities to test gravitation. By using an interplanetary spacecraft as a test mass, it is possible to test General Relativity at the Solar System distance scale. This requires to compute accurately the trajectory of the spacecraft, a process which relies on radio tracking and is limited by the uncertainty on the spacecraft non-gravitational acceleration.
The Gravity Advanced Package (GAP) is designed to measure the non-gravitational acceleration without bias. It is composed of an electrostatic accelerometer supplemented by a rotating stage. This article presents the instrument and its performances, and describes the method to make unbiased measurements. Finally, it addresses briefly the improvement brought by the instrument as far as orbit reconstruction is concerned.

abs pdf

Oct 04, 2011

1110.0342 (/preprints)
2011-10-04, 17:39 [edit]


[1110.0109] Relativistic Two-Body Coulomb-Breit Hamiltonian in an External Weak Gravitational Field

Authors: J. A. Caicedo, L. F. Urrutia

Date: 1 Oct 2011

Abstract: A construction of the Coulomb-Breit Hamiltonian for a pair of fermions, considered as a quantum two-body system, immersed in an arbitrary background gravitational field described by Einstein's General Relativity is presented. Working with Fermi normal coordinates for a freely falling observer in a spacetime region where there are no background sources and ignoring the gravitational back-reaction of the system, the effective Coulomb-Breit Hamiltonian is obtained starting from the S-matrix element corresponding to the one-photon exchange between the charged fermionic currents. The contributions due to retardation are considered up to order (v/c)ˆ2 and they are subsequently written as effective operators in the relativistic quantum mechanical Hilbert space of the system. The final Hamiltonian includes effects linear in the curvature and up to order (v/c)ˆ2.

abs pdf

Oct 04, 2011

1110.0109 (/preprints)
2011-10-04, 17:39 [edit]


[1109.6848] Perturbative, Post-Newtonian, and General Relativistic Dynamics of Black Hole Binaries

Authors: Alexandre Le Tiec

Date: 30 Sep 2011

Abstract: The orbital motion of inspiralling and coalescing black hole binaries can be investigated using a variety of approximation schemes and numerical methods within general relativity: post-Newtonian expansions, black hole perturbation theory, numerical relativity, and the effective-one-body formalism. We review two recent comparisons of the predictions from these various techniques. Both comparisons rely on the calculation of a coordinate invariant relation, in the case of non-spinning binary black holes on quasi-circular orbits. All methods are shown to agree very well in their common domain of validity.

abs pdf

Oct 03, 2011

1109.6848 (/preprints)
2011-10-03, 12:24 [edit]


[1005.1614] Faster Than Light?

Authors: Robert Geroch

Date: 10 May 2010

Abstract: It is argued that special relativity remains a viable physical theory even when there is permitted signals traveling faster than light.

abs pdf

Oct 01, 2011

1005.1614 (/preprints)
2011-10-01, 21:14 [edit]


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