[1010.5781] The impact of realistic models of mass segregation on the event rate of extreme-mass ratio inspirals and cusp re-growth

Authors: Pau Amaro-Seoane, Miguel Preto

Date: 27 Oct 2010

Abstract: One of the most interesting sources of gravitational waves (GWs) for LISA is the inspiral of compact objects on to a massive black hole (MBH), commonly referred to as an "extreme-mass ratio inspiral" (EMRI). The small object, typically a stellar black hole (bh), emits significant amounts of GW along each orbit in the detector bandwidth. The slowly, adiabatic inspiral of these sources will allow us to map space-time around MBHs in detail, as well as to test our current conception of gravitation in the strong regime. The event rate of this kind of source has been addressed many times in the literature and the numbers reported fluctuate by orders of magnitude. On the other hand, recent observations of the Galactic center revealed a dearth of giant stars inside the inner parsec relative to the numbers theoretically expected for a fully relaxed stellar cusp. The possibility of unrelaxed nuclei (or, equivalently, with no or only a very shallow cusp) adds substantial uncertainty to the estimates. Having this timely question in mind, we run a significant number of direct-summation $N-$body simulations with up to half a million particles to calibrate a much faster orbit-averaged Fokker-Planck code. We then investigate the regime of strong mass segregation (SMS) for models with two different stellar mass components. We show that, under quite generic initial conditions, the time required for the growth of a relaxed, mass segregated stellar cusp is shorter than a Hubble time for MBHs with $M_\bullet \lesssim 5 \times 10ˆ6 M_\odot$ (i.e. nuclei in the range of LISA). SMS has a significant impact boosting the EMRI rates by a factor of $\sim 10$ for our fiducial models of Milky Way type galactic nuclei.

abs pdf

Oct 31, 2010

1010.5781 (/preprints)
2010-10-31, 22:56 [edit]


[1010.5788] Shapiro delay measurement of a two solar mass neutron star

Authors: Paul Demorest, Tim Pennucci, Scott Ransom, Mallory Roberts, Jason Hessels

Date: 27 Oct 2010

Abstract: Neutron stars are composed of the densest form of matter known to exist in our universe, and thus provide a unique laboratory for exploring the properties of cold matter at super-nuclear density. Measurements of the masses or radii of these objects can strongly constrain the neutron-star matter equation of state, and consequently the interior composition of neutron stars. Neutron stars that are visible as millisecond radio pulsars are especially useful in this respect, as timing observations of the radio pulses provide an extremely precise probe of both the pulsar's motion and the surrounding space-time metric. In particular, for a pulsar in a binary system, detection of the general relativistic Shapiro delay allows us to infer the masses of both the neutron star and its binary companion to high precision. Here we present radio timing observations of the binary millisecond pulsar PSR J1614-2230, which show a strong Shapiro delay signature. The implied pulsar mass of 1.97 +/- 0.04 M_sun is by far the highest yet measured with such certainty, and effectively rules out the presence of hyperons, bosons, or free quarks at densities comparable to the nuclear saturation density.

abs pdf

Oct 31, 2010

1010.5788 (/preprints)
2010-10-31, 22:56 [edit]


[1010.6192] Source localization with an advanced gravitational wave detector network

Authors: Stephen Fairhurst

Date: 29 Oct 2010

Abstract: We derive an expression for the accuracy with which sources can be localized using a network of gravitational wave detectors. The result is obtained via triangulation, using timing accuracies at each detector and is applicable to a network with any number of detectors. We use this result to investigate the ability of advanced gravitational wave detector networks to accurately localize signals from compact binary coalescences. We demonstrate that additional detectors can significantly improve localization results and illustrate our findings with networks comprised of the advanced LIGO, advanced Virgo and LCGT. In addition, we evaluate the benefits of relocating one of the advanced LIGO detectors to Australia.

abs pdf

Oct 31, 2010

1010.6192 (/preprints)
2010-10-31, 22:56 [edit]


[1010.5790] The Massive Pulsar PSR J1614-2230: Linking Quantum Chromodynamics, Gamma-ray Bursts, and Gravitational Wave Astronomy

Authors: Feryal Ozel, Dimitrios Psaltis, Scott Ransom, Paul Demorest, Mark Alford

Date: 27 Oct 2010

Abstract: The recent measurement of the Shapiro delay in the radio pulsar PSR J1614-2230 yielded a mass of 1.97 +/- 0.04 M_sun, making it the most massive pulsar known to date. Its mass is high enough that, even without an accompanying measurement of the stellar radius, it has a strong impact on our understanding of nuclear matter, gamma-ray bursts, and the generation of gravitational waves from coalescing neutron stars. This single high mass value indicates that a transition to quark matter in neutron-star cores can occur at densities comparable to the nuclear saturation density only if the quarks are strongly interacting and are color superconducting. We further show that a high maximum neutron-star mass is required if short duration gamma-ray bursts are powered by coalescing neutron stars and, therefore, this mechanism becomes viable in the light of the recent measurement. Finally, we argue that the low-frequency (<= 500 Hz) gravitational waves emitted during the final stages of neutron-star coalescence encode the properties of the equation of state because neutron stars consistent with this measurement cannot be centrally condensed. This will facilitate the measurement of the neutron star equation of state with Advanced LIGO/Virgo.

abs pdf

Oct 31, 2010

1010.5790 (/preprints)
2010-10-31, 22:56 [edit]


[1010.5550] Black Hole Formation in Failing Core-Collapse Supernovae

Authors: Evan O&#x27;Connor, Christian D. Ott

Date: 27 Oct 2010

Abstract: We present results of a systematic study of failing core-collapse supernovae and the formation of stellar-mass black holes (BHs). Using our open-source general-relativistic 1.5D code GR1D equipped with a 3-flavor neutrino leakage/heating scheme and over 60 presupernova models, we study the effects of the choice of nuclear equation of state, zero-age main sequence (ZAMS) mass and metallicity, rotation, and mass loss prescription on BH formation. We find that the outcome of collapse, for a given equation of state, can be predicted, to first order, by a single parameter, the compactness of the stellar core at bounce. By comparing protoneutron star (PNS) structure at the onset of gravitational instability with solutions of the TOV equations, we find that thermal pressure support in the outer PNS core is responsible for raising the maximum PNS mass by up to 25% above the cold NS value. By artificially increasing neutrino heating, we find the critical neutrino heating efficiency required for exploding a given progenitor structure and connect these findings with ZAMS conditions, establishing, albeit approximately, for the first time based on actual collapse simulations, the mapping between ZAMS parameters and the outcome of core collapse. We also study the effect of progenitor rotation and find that the dimensionless spin of nascent black holes may be robustly limited below a* = Jc/GMˆ2 = 1 by the appearance of nonaxisymmetric rotational instabilities.

abs pdf

Oct 31, 2010

1010.5550 (/preprints)
2010-10-31, 22:55 [edit]


[1010.5245] A Precision Test for an Extra Spatial Dimension Using Black Hole--Pulsar Binaries

Authors: John H. Simonetti, Michael Kavic, Djordje Minic, Umair Surani, Vipin Vejayan

Date: 25 Oct 2010

Abstract: e discuss the observable effects of enhanced black-hole mass loss in a black hole--neutron star (BH--NS) binary, due to the presence of a warped extra spatial dimension of curvature radius $L$ in the braneworld scenario. For some masses and orbital parameters in the expected ranges the binary components would outspiral, the opposite of the behavior due to energy loss from gravitational radiation alone. If the NS is a pulsar, observations of the rate of change of the orbital period with a precision obtained for the Binary Pulsar B1913+16 could easily detect the effect of mass loss. For $M_{BH}=7M_\odot$, $M_{NS}=1.4M_\odot$, eccentricity $e=0.1$, and $L=10\mu$m, the critical orbital period dividing systems which inspiral from systems which outspiral is P$\approx$6.5~hours, which is within the range of expected orbital periods; this value drops to P$\approx$4.2~hours for $M_{BH}=5M_\odot$. Observations of a BH--pulsar system could set considerably better limits on $L$ in these braneworld models than could be determined by torsion-balance gravity experiments in the foreseeable future.

abs pdf

Oct 26, 2010

1010.5245 (/preprints)
2010-10-26, 22:20 [edit]


[1010.5260] Black-hole binaries, gravitational waves, and numerical relativity

Authors: Joan M. Centrella, John G. Baker, Bernard J. Kelly, James R. van Meter

Date: 25 Oct 2010

Abstract: Understanding the predictions of general relativity for the dynamical interactions of two black holes has been a long-standing unsolved problem in theoretical physics. Black-hole mergers are monumental astrophysical events, releasing tremendous amounts of energy in the form of gravitational radiation, and are key sources for both ground- and space-based gravitational wave detectors. The black-hole merger dynamics and the resulting gravitational waveforms can only be calculated through numerical simulations of Einstein's equations of general relativity. For many years, numerical relativists attempting to model these mergers encountered a host of problems, causing their codes to crash after just a fraction of a binary orbit could be simulated. Recently, however, a series of dramatic advances in numerical relativity has, for the first time, allowed stable, robust black hole merger simulations. We chronicle this remarkable progress in the rapidly maturing field of numerical relativity, and the new understanding of black-hole binary dynamics that is emerging. We also discuss important applications of these fundamental physics results to astrophysics, to gravitational-wave astronomy, and in other areas.

abs pdf

Oct 26, 2010

1010.5260 (/preprints)
2010-10-26, 22:20 [edit]


[1010.5246] Prospects for Direct Detection of Inflationary Gravitational Waves by Next Generation Interferometric Detectors

Authors: Sachiko Kuroyanagi, Takeshi Chiba, Naoshi Sugiyama

Date: 25 Oct 2010

Abstract: We study the potential impact of detecting the inflationary gravitational wave background by the future space-based gravitational wave detectors, such as DECIGO and BBO. The signal-to-noise ratio of each experiment is calculated for chaotic/natural/hybrid inflation models by using the precise predictions of the gravitational wave spectrum based on numerical calculations. We investigate the dependence of each inflation model on the reheating temperature which influences the amplitude and shape of the spectrum, and find that the gravitational waves could be detected for chaotic/natural inflation models with high reheating temperature. From the detection of the gravitational waves, a lower bound on the reheating temperature could be obtained. The implications of this lower bound on the reheating temperature for particle physics are also discussed.

abs pdf

Oct 26, 2010

1010.5246 (/preprints)
2010-10-26, 22:20 [edit]


[1010.5200] Exploring the Use of Numerical Relativity Waveforms in Burst Analysis of Precessing Black Hole Mergers

Authors: Sebastian Fischetti, James Healy, Laura Cadonati, Lionel London, Satyanarayan R.P. Mohapatra, Deirdre Shoemaker

Date: 25 Oct 2010

Abstract: Recent years have witnessed tremendous progress in numerical relativity and an ever improving performance of ground-based interferometric gravitational wave detectors. In preparation for Advanced LIGO and a new era in gravitational wave astronomy, the numerical relativity and gravitational wave data analysis communities are collaborating to ascertain the most useful role for numerical relativity waveforms in the detection and characterization of binary black hole coalescences. In this paper, we explore the detectability of equal mass, merging black hole binaries with precessing spins and total mass M_T in [80,350]Msol, using numerical relativity waveforms and template-less search algorithms designed for gravitational wave bursts. In particular, we present a systematic study using waveforms produced by the MAYAKRANC code that are added to colored, Gaussian noise and analyzed with the Omega burst search algorithm. Detection efficiency is weighed against the orientation of one of the black-hole's spin axes. We find a strong correlation between the detection efficiency and the radiated energy and angular momentum, and that the inclusion of the l=2, m=+/-1,0 modes, at a minimum, is necessary to account for the full dynamics of precessing systems.

abs pdf

Oct 26, 2010

1010.5200 (/preprints)
2010-10-26, 11:29 [edit]


[1010.4843] DAME: A Web Oriented Infrastructure for Scientific Data Mining & Exploration

Authors: Massimo Brescia, Giuseppe Longo, George S. Djorgovski, Stefano Cavuoti, Raffaele D&#x27;Abrusco, Ciro Donalek, Alessandro Di Guido, Michelangelo Fiore, Mauro Garofalo, Omar Laurino, Ashish Mahabal, Francesco Manna, Alfonso Nocella, Giovanni d&#x27;Angelo, Maurizio Paolillo

Date: 23 Oct 2010

Abstract: Nowadays, many scientific areas share the same need of being able to deal with massive and distributed datasets and to perform on them complex knowledge extraction tasks. This simple consideration is behind the international efforts to build virtual organizations such as, for instance, the Virtual Observatory (VObs). DAME (DAta Mining & Exploration) is an innovative, general purpose, Web-based, VObs compliant, distributed data mining infrastructure specialized in Massive Data Sets exploration with machine learning methods. Initially fine tuned to deal with astronomical data only, DAME has evolved in a general purpose platform which has found applications also in other domains of human endeavor. We present the products and a short outline of a science case, together with a detailed description of DAMEs main features and architecture.

abs pdf

Oct 26, 2010

1010.4843 (/preprints)
2010-10-26, 11:29 [edit]


[1010.4526] An extended solution space for Chern-Simons gravity: the slowly rotating Kerr black hole

Authors: Mauro Cambiaso, Luis F. Urrutia

Date: 21 Oct 2010

Abstract: In the Einstein-Cartan formulation, an iterative procedure to find solutions in non-dynamical Chern-Simons (CS) gravity in vacuum is proposed. The iterations, in powers of a small parameter $\beta$ which codifies the CS coupling, start from an arbitrary torsionless solution of Einstein equations. With Schwarzschild as the zeroth-order choice, we derive a second-order differential equation for the $\mathcal{O}(\beta)$ corrections to the metric, for an arbitrary zeroth-order embedding parameter. In particular, the slowly rotating Kerr metric is an $\mathcal{O}(\beta)$ solution in either the canonical or the axial embeddings.

abs pdf

Oct 24, 2010

1010.4526 (/preprints)
2010-10-24, 22:03 [edit]


[1010.4337] Pulsar timing arrays as imaging gravitational wave telescopes: angular resolution and source (de)confusion

Authors: Latham Boyle, Ue-Li Pen

Date: 20 Oct 2010

Abstract: Pulsar timing arrays (PTAs) will be sensitive to a finite number of gravitational wave (GW) "point" sources (e.g. supermassive black hole binaries). N quiet pulsars with accurately known distances d_{pulsar} can characterize up to 2N/7 distant chirping sources per frequency bin \Delta f_{gw}=1/T, and localize them with "diffraction limited" precision \delta\theta \gtrsim (1/SNR)(\lambda_{gw}/d_{pulsar}). Even if the pulsar distances are poorly known, a PTA with F frequency bins can still characterize up to (2N/7)[1-(1/2F)] sources per bin, and the quasi-singular pattern of timing residuals in the vicinity of a GW source still allows the source to be localized quasi-topologically within roughly the smallest quadrilateral of quiet pulsars that encircles it on the sky, down to a limiting resolution \delta\theta \gtrsim (1/SNR) \sqrt{\lambda_{gw}/d_{pulsar}}. PTAs may be unconfused, even at the lowest frequencies, with matched filtering always appropriate.

abs pdf

Oct 24, 2010

1010.4337 (/preprints)
2010-10-24, 22:03 [edit]


[1009.0738] Spectral Representations of Neutron-Star Equations of State

Authors: Lee Lindblom

Date: 3 Sep 2010

Abstract: Methods are developed for constructing spectral representations of cold (barotropic) neutron-star equations of state. These representations are faithful in the sense that every physical equation of state has a representation of this type, and conversely every such representation satisfies the minimal thermodynamic stability criteria required of any physical equation of state. These spectral representations are also efficient, in the sense that only a few spectral coefficients are generally required to represent neutron-star equations of state quiet accurately. This accuracy and efficiency is illustrated by constructing spectral fits to a large collection of "realistic" neutron-star equations of state.

abs pdf

Oct 24, 2010

1009.0738 (/preprints)
2010-10-24, 22:03 [edit]


[1010.3942] Kinks, extra dimensions, and gravitational waves

Authors: Eimear O&#x27;Callaghan, Ruth Gregory

Date: 19 Oct 2010

Abstract: We investigate in detail the gravitational wave signal from kinks on cosmic (super)strings, including the kinematical effects from the internal extra dimensions. We find that the signal is suppressed, however, the effect is less significant that that for cusps. Combined with the greater incidence of kinks on (super)strings, it is likely that the kink signal offers the better chance for detection of cosmic (super)strings.

abs pdf

Oct 20, 2010

1010.3942 (/preprints)
2010-10-20, 10:10 [edit]


[1010.3865] The gravitational wave energy spectrum of a parabolic encounter

Authors: Christopher P. L. Berry, Jonathan R. Gair

Date: 19 Oct 2010

Abstract: We derive an analytic expression for the energy spectrum of gravitational waves from a parabolic Keplerian binary by taking the limit of the Peters and Matthews spectrum for eccentric orbits. This demonstrates that the location of the peak of the energy spectrum depends primarily on the orbital periapse rather than the eccentricity. We compare this weak-field result to strong-field calculations and find it is reasonably accurate (~10%) provided that the azimuthal and radial orbital frequencies do not differ by more than ~10%. For equatorial orbits in the Kerr spacetime, this corresponds to periapse radii of rp \geq 20M. These results can be used to model radiation bursts from compact objects on highly eccentric orbits about massive black holes in the local Universe, which could be detected by LISA.

abs pdf

Oct 20, 2010

1010.3865 (/preprints)
2010-10-20, 10:08 [edit]


[1010.3420] Experimental Search for Quantum Gravity

Authors: Sabine Hossenfelder

Date: 17 Oct 2010

Abstract: We offer a brief survey of existent and planned experimental tests for quantum gravity. First, we outline the questions we wish to address, and then introduce some of the phenomenological models that are currently used in quantum gravity, both with and without a lowered Planck scale. After that, we summarize experimental areas where these models can be tested or constrained and discuss the status of the field.

abs pdf

Oct 19, 2010

1010.3420 (/preprints)
2010-10-19, 14:36 [edit]


[1010.3218] Horava-Lifshitz gravity: a status report

Authors: Thomas P. Sotiriou

Date: 15 Oct 2010

Abstract: This is intended to be a brief introduction and overview of Horava-Lifshitz gravity. The motivation and all of the various version of the theory (to date) are presented. The dynamics of the theory are discussed in some detail, with a focus on low energy viability and consistency, as these have been the issues that attracted most of the attention in the literature so far. Other properties of the theory and developments within its framework are also covered, such as: its relation to Einstein-aether theory, cosmology, and future perspectives.

abs pdf

Oct 18, 2010

1010.3218 (/preprints)
2010-10-18, 12:45 [edit]


[1010.3250] Electromagnetic Counterparts to Black Hole Mergers

Authors: Jeremy D. Schnittman

Date: 15 Oct 2010

Abstract: During the final moments of a binary black hole (BH) merger, the gravitational wave (GW) luminosity of the system is greater than the combined electromagnetic output of the entire observable universe. However, the extremely weak coupling between GWs and ordinary matter makes these waves very difficult to detect directly. Fortunately, the inspiraling BH system will interact strongly--on a purely Newtonian level--with any surrounding material in the host galaxy, and this matter can in turn produce unique electromagnetic (EM) signals detectable at Earth. By identifying EM counterparts to GW sources, we will be able to study the host environments of the merging BHs, in turn greatly expanding the scientific yield of a mission like LISA.

abs pdf

Oct 18, 2010

1010.3250 (/preprints)
2010-10-18, 12:45 [edit]


[1010.2879] Banks of templates for directed searches of gravitational waves from spinning neutron stars

Authors: Andrzej Pisarski, Piotr Jaranowski, Maciej Pietka

Date: 14 Oct 2010

Abstract: We construct efficient banks of templates suitable for directed searches of almost monochromatic gravitational waves originating from spinning nuetron stars in our Galaxy in data being collected by currently operating interferometric detectors. We thus assume that the position of the gravitational-wave source in the sky is known, but we do not assume that the wave's frequency and its derivatives are a priori known. In the construction we employ simplified model of the signal with constant amplitude and phase which is a polynomial function of time. All our template banks enable usage of the fast Fourier transform algorithm in the computation of the maximum-likelihood F-statistic for nodes of the grids defining the bank. We study and employ the dependence of the grid's construction on the choice of the position of the observational interval with respect to the origin of time axis. We also study the usage of the fast Fourier transform algorithms with non-standard frequency resolutions achieved by zero padding or folding the data. In the case of the gravitational-wave signal with one spindown parameter included we have found grids with covering thicknesses which are only 0.1%--16% larger than the thickness of the optimal two-dimensional hexagonal covering.

abs pdf

Oct 15, 2010

1010.2879 (/preprints)
2010-10-15, 14:11 [edit]


[1010.2777] Simulating merging binary black holes with nearly extremal spins

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

Date: 13 Oct 2010

Abstract: Astrophysically realistic black holes may have spins that are nearly extremal (i.e., close to 1 in dimensionless units). Numerical simulations of binary black holes — important tools both for calibrating analytical templates for gravitational-wave detection and for exploring the nonlinear dynamics of curved spacetime — are particularly challenging when the holes' spins are nearly extremal. Typical initial data methods cannot yield simulations with nearly extremal spins; e.g., Bowen-York data cannot produce simulations with spins larger than about 0.93. In this paper, we present the first binary black hole inspiral, merger, and ringdown with initial spins larger than the Bowen-York limit. Specifically, using the Spectral Einstein Code (SpEC), we simulate the inspiral (through 12.5 orbits), merger and ringdown of two equal-mass black holes with equal spins of magnitude 0.95 antialigned with the orbital angular momentum.

abs pdf

Oct 15, 2010

1010.2777 (/preprints)
2010-10-15, 14:11 [edit]


[0811.1602] Double Compact Objects as Low-frequency Gravitational Wave Sources

Authors: Krzysztof Belczynski, Matthew Benacquista, Tomasz Bulik

Date: 10 Nov 2008

Abstract: We study the Galactic field population of double compact objects (NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with LISA at low gravitational-wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contribution from the disk, bulge and halo. Although the Galaxy hosts 10ˆ5 double compact object binaries emitting low-frequency gravitational waves, only a handful of these objects in the disk will be detectable with LISA, but none from the halo or bulge. This is because the bulk of these binaries are NS-NS systems with high eccentricities and long orbital periods (weeks/months) causing inefficient signal accumulation (small number of signal bursts at periastron passage in 1 yr of LISA observations) rendering them undetectable in the majority of these cases. We adopt two evolutionary models that differ in their treatment of the common envelope phase that is a major (and still mostly unknown) process in the formation of close double compact objects. Depending on the adopted evolutionary model, our calculations indicate the likely detection of about 4 NS-NS binaries and 2 BH-BH systems (model A; likely survival of progenitors through CE) or only a couple of NS-NS binaries (model B; suppression of the double compact object formation due to CE mergers).

abs pdf

Oct 13, 2010

0811.1602 (/preprints)
2010-10-13, 22:41 [edit]


[1010.2553] Conservative corrections to the innermost stable circular orbit (ISCO) of a Kerr black hole: a new gauge-invariant post-Newtonian ISCO condition, and the ISCO shift due to test-particle spin and the gravitational self-force

Authors: Marc Favata

Date: 13 Oct 2010

Abstract: The innermost stable circular orbit (ISCO) delimits the transition from circular orbits to those that plunge into a black hole. In the test-mass limit, well-defined ISCO conditions exist for the Kerr and Schwarzschild spacetimes. In the finite-mass case, there are a large variety of ways to define an ISCO in a post-Newtonian (PN) context. Here I generalize the gauge-invariant ISCO condition of Blanchet & Iyer (2003) to the case of spinning (non-precessing) binaries. The Blanchet-Iyer ISCO condition has two desirable and unexpected properties: (1) it exactly reproduces the Schwarzschild ISCO in the test-mass limit, and (2) it accurately approximates the recently-calculated shift in the Schwarzschild ISCO frequency due to the conservative-piece of the gravitational self-force [Barack & Sago (2009)]. The generalization of this ISCO condition to spinning binaries has the property that it also exactly reproduces the Kerr ISCO in the test-mass limit (up to the order at which PN spin corrections are currently known). The shift in the ISCO due to the spin of the test-particle is also calculated. Remarkably, the gauge-invariant PN ISCO condition exactly reproduces the ISCO shift predicted by the Papapetrou equations for a fully-relativistic spinning particle. It is surprising that an analysis of the stability of the standard PN equations of motion is able (without any form of "resummation") to accurately describe strong-field effects of the Kerr spacetime. The ISCO frequency shift due to the conservative self-force in Kerr is also calculated from this new ISCO condition, as well as from the effective-one-body Hamiltonian of Barausse & Buonanno (2010). These results serve as a useful point-of-comparison for future gravitational self-force calculations in the Kerr spacetime.

abs pdf

Oct 13, 2010

1010.2553 (/preprints)
2010-10-13, 22:36 [edit]


[1010.2496] Properties of Accretion Flows Around Coalescing Supermassive Black Holes

Authors: Tamara Bogdanovic (University of Maryland), Tanja Bode, Roland Haas, Pablo Laguna, Deirdre Shoemaker (Georgia Institute of Technology)

Date: 12 Oct 2010

Abstract: What are the properties of accretion flows in the vicinity of coalescing supermassive black holes (SBHs)? The answer to this question has direct implications for the feasibility of coincident detections of electromagnetic (EM) and gravitational wave (GW) signals from coalescences. Such detections are considered to be the next observational grand challenge that will enable testing general relativity in the strong, nonlinear regime and improve our understanding of evolution and growth of these massive compact objects. In this paper we review the properties of the environment of coalescing binaries in the context of the circumbinary disk and hot, radiatively inefficient accretion flow models and use them to mark the extent of the parameter space spanned by this problem. We report the results from an initial, general relativistic, hydrodynamical study of the inspiral and merger of equal-mass, spinning black holes, motivated by the latter scenario. We find that correlated EM+GW oscillations can arise during the inspiral phase followed by the gradual rise and subsequent drop-off in the light curve at the time of coalescence. While there are indications that the latter EM signature is a more robust one, a detection of either signal coincidentally with GWs would be a convincing evidence for an impending SBH binary coalescence. The observability of an EM counterpart in the hot accretion flow scenario depends on the details of a model. In the case of the most massive binaries observable by the Laser Interferometer Space Antenna, upper limits on luminosity imply that they may be identified by EM searches out to z~0.1-1. However, given the radiatively inefficient nature of the gas flow, we speculate that a majority of massive binaries may appear as low luminosity AGN in the local universe.

abs pdf

Oct 13, 2010

1010.2496 (/preprints)
2010-10-13, 22:35 [edit]


[1010.2086] Gravitational wave astronomy: the definitive test for the "Einstein frame versus Jordan frame" controversy

Authors: Christian Corda

Date: 11 Oct 2010

Abstract: The potential realization of a gravitational wave (GW) astronomy in next years is a great challenge for the scientific community. By giving a significant amount of new information, GWs will be a cornerstone for a better understanding of the universe and of the gravitational physics. In this paper the author shows that the GW astronomy will permit to solve a captivating issue of gravitation as it will be the definitive test for the famous "Einstein frame versus Jordan frame" controversy. In fact, we show that the motion of the test masses, i.e. the beam splitter and the mirror in the case of an interferometer, which is due to the scalar component of a GW, is different in the two frames. Thus, if a consistent GW astronomy will be realized, an eventual detection of signals of scalar GWs will permit to discriminate among the two frames. In this way, a direct evidence from observations will solve in an ultimate way the famous and long history of the "Einstein frame versus Jordan frame" controversy.

abs pdf

Oct 12, 2010

1010.2086 (/preprints)
2010-10-12, 14:12 [edit]


[1010.2165] The Final Merger of Black-Hole Binaries

Authors: Joan M. Centrella, John G. Baker, Bernard J. Kelly, James R. van Meter

Date: 11 Oct 2010

Abstract: Recent breakthroughs in the field of numerical relativity have led to dramatic progress in understanding the predictions of General Relativity for the dynamical interactions of two black holes in the regime of very strong gravitational fields. Such black-hole binaries are important astrophysical systems and are a key target of current and developing gravitational-wave detectors. The waveform signature of strong gravitational radiation emitted as the black holes fall together and merge provides a clear observable record of the process. After decades of slow progress, these mergers and the gravitational-wave signals they generate can now be routinely calculated using the methods of numerical relativity. We review recent advances in understanding the predicted physics of events and the consequent radiation, and discuss some of the impacts this new knowledge is having in various areas of astrophysics.

abs pdf

Oct 12, 2010

1010.2165 (/preprints)
2010-10-12, 14:12 [edit]


[1010.1641] The Effect of Data Gaps on LISA Galactic Binary Parameter Estimation

Authors: J&#xe9;r&#xf4;me Carr&#xe9;, Edward K. Porter

Date: 8 Oct 2010

Abstract: In the last few years there has been an enormous effort in parameter estimation studies for different sources with the space based gravitational wave detector, LISA. While these studies have investigated sources of differing complexity, the one thing they all have in common is they assume continuous data streams. In reality, the LISA data stream will contain gaps from such possible events such as repointing of the satellite antennae, to discharging static charge build up on the satellites, to disruptions due to micro-meteor strikes. In this work we conduct a large scale Monte Carlo parameter estimation simulation for galactic binaries assuming data streams containing gaps. As the expected duration and frequency of the gaps are currently unknown, we have decided to focus on gaps of approximately one hour, occurring either once per day or once per week. We also study the case where, as well as the expected periodic gaps, we have a data drop-out of one continuous week. Our results show that for for galactic binaries, a gap of once per week introduces a bias of between 0.5% and 1% in the estimation of parameters, for the most important parameters such as the sky position, amplitude and frequency. This number rises to between 3% and 7% for the case of one gap a day, and to between 4% and 9% when we have one gap a day and a spurious gap of a week. A future study will investigate the effect of data gaps on supermassive black hole binaries and extreme mass ratio inspirals.

abs pdf

Oct 10, 2010

1010.1641 (/preprints)
2010-10-10, 22:45 [edit]


[1010.1535] Secular Stellar Dynamics near a Massive Black Hole

Authors: Ann-Marie Madigan, Clovis Hopman, Yuri Levin

Date: 7 Oct 2010

Abstract: The angular momentum evolution of stars close to massive black holes (MBHs) is driven by secular torques. In contrast to two-body relaxation, where interactions between stars are incoherent, the resulting resonant relaxation (RR) process is characterized by coherence times of hundreds of orbital periods. In this paper, we show that all the statistical properties of RR can be reproduced in an autoregressive moving average (ARMA) model. We use the ARMA model, calibrated with extensive N-body simulations, to analyze the long-term evolution of stellar systems around MBHs with Monte Carlo simulations. We show that for a single mass system in steady state, a depression is carved out near a MBH as a result of tidal disruptions. In our Galactic center, the size of the depression is about 0.2 pc, consistent with the size of the observed "hole" in the distribution of bright late-type stars. We also find that the velocity vectors of stars around a MBH are locally not isotropic. In a second application, we evolve the highly eccentric orbits that result from the tidal disruption of binary stars, which are considered to be plausible precursors of the "S-stars" in the Galactic center. We find that in this scenario more highly eccentric (e > 0.9) S-star orbits are produced than have been observed to date.

abs pdf

Oct 10, 2010

1010.1535 (/preprints)
2010-10-10, 19:36 [edit]


[1010.1721] The Effect of Massive Perturbers on Extreme Mass-Ratio Inspiral Waveforms

Authors: Nicolas Yunes, M. Coleman Miller, Jonathan Thornburg

Date: 8 Oct 2010

Abstract: Extreme mass ratio inspirals, in which a stellar-mass object merges with a supermassive black hole, are prime sources for space-based gravitational wave detectors because they will facilitate tests of strong gravity and probe the spacetime around rotating compact objects. In the last few years of such inspirals, the total phase is in the millions of radians and details of the waveforms are sensitive to small perturbations. We show that one potentially detectable perturbation is the presence of a second supermassive black hole within a few tenths of a parsec. The acceleration produced by the perturber on the extreme mass-ratio system produces a steady drift that causes the waveform to deviate systematically from that of an isolated system. If the perturber is a few tenths of a parsec from the extreme-mass ratio system (plausible in as many as a few percent of cases) higher derivatives of motion might also be detectable. In that case, the mass and distance of the perturber can be derived independently, which would allow a new probe of merger dynamics.

abs pdf

Oct 10, 2010

1010.1721 (/preprints)
2010-10-10, 19:36 [edit]


[1010.1000] Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. III. Quasi-Periodic Variability

Authors: Tim Johannsen (Arizona), Dimitrios Psaltis (Arizona)

Date: 5 Oct 2010

Abstract: According to the no-hair theorem, astrophysical black holes are uniquely described by their masses and spins. An observational test of the no-hair theorem can be performed by measuring at least three different multipole moments of the spacetime of a black hole and verifying whether their values are consistent with the unique combinations of the Kerr solution. In this paper, we study quasi-periodic variability observed in the emission from black holes across the electromagnetic spectrum as a test of the no-hair theorem. We derive expressions for the Keplerian and epicyclic frequencies in a quasi-Kerr spacetime, in which the quadrupole moment is a free parameter in addition to mass and spin. We show that, for moderate spins, the Keplerian frequency is practically independent of small deviations of the quadrupole moment from the Kerr value, while the epicyclic frequencies exhibit significant variations. We apply this framework to quasi-periodic oscillations in black-hole X-ray binaries in two different scenarios. In the case that a pair of quasi-periodic oscillations can be identified as the fundamental g- and c-modes in the accretion disk, we show that the no-hair theorem can be tested in conjunction with an independent mass measurement. If, on the other hand, the pairs of oscillations are identified with non-parametric resonance of dynamical frequencies in the accretion disk, then testing the no-hair theorem also requires an independent measurement of the black-hole spin. In addition, we argue that VLBI observations of Sgr A* may test the no-hair theorem through a combination of imaging observations and the detection of quasi-periodic variability.

abs pdf

Oct 07, 2010

1010.1000 (/preprints)
2010-10-07, 12:24 [edit]


[1010.0062] Testing Modified Gravity with Gravitational Wave Astronomy

Authors: Carlos F. Sopuerta, Nicolas Yunes

Date: 1 Oct 2010

Abstract: The emergent area of gravitational wave astronomy promises to provide revolutionary discoveries in the areas of astrophysics, cosmology, and fundamental physics. One of the most exciting possibilities is to use gravitational-wave observations to test alternative theories of gravity. In this contribution we describe how to use observations of extreme-mass-ratio inspirals by the future Laser Interferometer Space Antenna to test a particular class of theories: Chern-Simons modified gravity.

abs pdf

Oct 03, 2010

1010.0062 (/preprints)
2010-10-03, 18:48 [edit]


[1008.0384] Approximate analytic expressions for circular orbits around rapidly rotating compact stars

Authors: M. Bejger, J. L. Zdunik, P. Haensel

Date: 2 Aug 2010

Abstract: We calculate stationary configurations of rapidly rotating compact stars in general relativity, to study the properties of circular orbits of test particles in the equatorial plane. We search for simple, but precise, analytical formulae for the orbital frequency, specific angular momentum and binding energy of a test particle, valid for any equation of state and for any rotation frequency of the rigidly rotating compact star, up to the mass-shedding limit. Numerical calculations are performed using precise 2-D codes based on multi-domain spectral methods. Models of rigidly rotating neutron stars and the space-time outside them are calculated for several equations of state of dense matter. Calculations are also performed for quark stars consisting of self-bound quark matter. At the mass-shedding limit, the rotational frequency converges to a Schwarzschildian orbital frequency at the equator. We show that orbital frequency for any orbit outside equator is also approximated by a Schwarzschildian formula. Using a simple approximation for the frame-dragging term, we obtain approximate expressions for the specific angular momentum and specific energy on the corotating circular orbits in the equatorial plane of neutron star, which are valid down to the stellar equator. The formulae recover reference numerical values with typically 1% of accuracy for neutron stars with M > 0.5 M_sun. They are less precise for quark stars consisting of self-bound quark matter.

abs pdf

Oct 01, 2010

1008.0384 (/preprints)
2010-10-01, 09:12 [edit]


[1009.6073] An Efficient Time-Domain Method to Model Extreme-Mass-Ratio Inspirals

Authors: Priscilla Canizares, Carlos F. Sopuerta

Date: 30 Sep 2010

Abstract: The gravitational-wave signals emitted by Extreme-Mass-Ratio Inspirals will be hidden in the instrumental LISA noise and the foreground noise produced by galactic binaries in the LISA band. Then, we need accurate gravitational-wave templates to extract these signals from the noise and obtain the relevant physical parameters. This means that in the modeling of these systems we have to take into account how the orbit of the stellar-mass compact object is modified by the action of its own gravitational field. This effect can be described as the action of a local force, the self-force. We present a time-domain technique to compute the self-force for geodesic eccentric orbits around a non-rotating massive black hole. To illustrate the method we have applied it to a testbed model consisting of scalar charged particle orbiting a non-dynamical black hole. A key feature of our method is that it does not introduce a small scale associated with the stellar-mass compact object. This is achieved by using a multidomain framework where the particle is located at the interface between two subdomains. In this way, we just have to evolve homogeneous wave-like equations with smooth solutions that have to be communicated across the subdomain boundaries using appropriate junction conditions. The numerical technique that we use to implement this scheme is the pseudospectral collocation method. We show the suitability of this technique for the modeling of Extreme-Mass-Ratio Inspirals and show that it can provide accurate results for the self-force.

abs pdf

Oct 01, 2010

1009.6073 (/preprints)
2010-10-01, 09:12 [edit]


[1009.6172] Constraining properties of the black hole population using LISA

Authors: Jonathan R Gair, Alberto Sesana, Emanuele Berti, Marta Volonteri

Date: 30 Sep 2010

Abstract: LISA should detect gravitational waves from tens to hundreds of systems containing black holes with mass in the range from 10 thousand to 10 million solar masses. Black holes in this mass range are not well constrained by current electromagnetic observations, so LISA could significantly enhance our understanding of the astrophysics of such systems. In this paper, we describe a framework for combining LISA observations to make statements about massive black hole populations. We summarise the constraints that LISA observations of extreme-mass-ratio inspirals might be able to place on the mass function of black holes in the LISA range. We also describe how LISA observations can be used to choose between different models for the hierarchical growth of structure in the early Universe. We consider four models that differ in their prescription for the initial mass distribution of black hole seeds, and in the efficiency of accretion onto the black holes. We show that with as little as 3 months of LISA data we can clearly distinguish between these models, even under relatively pessimistic assumptions about the performance of the detector and our knowledge of the gravitational waveforms.

abs pdf

Oct 01, 2010

1009.6172 (/preprints)
2010-10-01, 09:12 [edit]


[1009.6013] Extreme Mass-Ratio Inspirals in the Effective-One-Body Approach: Quasi-Circular, Equatorial Orbits around a Spinning Black Hole

Authors: Nicolas Yunes, Alessandra Buonanno, Scott A. Hughes, Yi Pan, Enrico Barausse, M. Coleman Miller, William Throwe

Date: 29 Sep 2010

Abstract: We construct effective-one-body waveform models suitable for data analysis with LISA for extreme-mass ratio inspirals in quasi-circular, equatorial orbits about a spinning supermassive black hole. The accuracy of our model is established through comparisons against frequency-domain, Teukolsky-based waveforms in the radiative approximation. The calibration of eight high-order post-Newtonian parameters in the energy flux suffices to obtain a phase and fractional amplitude agreement of better than 1 radian and 1 % respectively over a period between 2 and 6 months depending on the system considered. This agreement translates into matches higher than 97 % over a period between 4 and 9 months, depending on the system. Better agreements can be obtained if a larger number of calibration parameters are included. Higher-order mass ratio terms in the effective-one-body Hamiltonian and radiation-reaction introduce phase corrections of at most 30 radians in a one year evolution. These corrections are usually one order of magnitude larger than those introduced by the spin of the small object in a one year evolution. These results suggest that the effective-one-body approach for extreme mass ratio inspirals is a good compromise between accuracy and computational price for LISA data analysis purposes.

abs pdf

Oct 01, 2010

1009.6013 (/preprints)
2010-10-01, 09:12 [edit]


[1009.5998] Accuracy and effectualness of closed-form, frequency-domain waveforms for non-spinning black hole binaries

Authors: T. Damour, M. Trias, A. Nagar

Date: 29 Sep 2010

Abstract: The coalescences of binary black hole (BBH) systems, here taken to be non-spinning, are among the most promising sources for gravitational wave (GW) ground-based detectors, such as LIGO and Virgo. To detect the GW signals emitted by BBHs, and measure the parameters of the source, one needs to have in hand a bank of GW templates that are both effectual (for detection), and accurate (for measurement). We study the effectualness and the accuracy of the two types of parametrized banks of templates that are directly defined in the frequency-domain by means of closed-form expressions, namely 'post-Newtonian' (PN) and 'phenomenological' models. In absence of knowledge of the exact waveforms, our study assumes as fiducial, target waveforms the ones generated by the most accurate version of the effective one body (EOB) formalism. We find that, for initial GW detectors the use, at each point of parameter space, of the best closed-form template (among PN and phenomenological models) leads to an effectualness >97% over the entire mass range and >99% in an important fraction of parameter space; however, when considering advanced detectors, both of the closed-form frequency-domain models fail to be effectual enough in significant domains of the two-dimensional [total mass and mass ratio] parameter space. Moreover, we find that, both for initial and advanced detectors, the two closed-form frequency-domain models fail to satisfy the minimal required accuracy standard in a very large domain of the two-dimensional parameter space. In addition, a side result of our study is the determination, as a function of the mass ratio, of the maximum frequency at which a frequency-domain PN waveform can be 'joined' onto a NR-calibrated EOB waveform without undue loss of accuracy.

abs pdf

Oct 01, 2010

1009.5998 (/preprints)
2010-10-01, 09:12 [edit]


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