by Shcherbakov, Roman V. and Penna, Robert F. and McKinney, Jonathan C.
17 pages, 13 figures, submitted to ApJ

The constraints on Sgr A* black hole (BH) and accretion flow parameters are found by fitting polarized sub-mm observations. The observations from 29 papers are averaged into a quasi-quiescent set. We run three-dimensional general relativistic magnetohydrodynamical (3D GRMHD) simulations for dimensionless spins a=0,0.5,0.7,0.9,0.98 till 20000M, construct an averaged dynamical model, perform GR polarized radiative transfer, and explore the parameter space of spin $latex a$, inclination angle \theta, position angle (PA), accretion rate \dot{M}, and electron temperature $latex T_e$ at 6M radius. The best-fitting model for spin a=0.9 gives \chi^2=0.99 with \theta=59deg, \dot{M}=1.3*10^{-8}M_sun/year, T_e=3.2*10^{10}K at 6M, the best-fitting model for spin a=0.5 gives \chi^2=0.84 with \theta=70deg, \dot{M}=7.0*10^{-8}M_sun/year, and T_p/T_e=22 at 6M with T_e=3.50*10^{10}K. We identify the physical phenomena leading to the matched linear polarization (LP), circular polarization (CP), and electric vector position angle (EVPA). Our statistical analysis reveals the most probable spin is a=0.9. The spin a=0.5 solutions are 10 times less probable despite giving lower minimum \chi^2 and spin a=0 is excluded as having probability P(a)<1%. Polarized data allows us to tightly constrain some quantities. Inclination angle, electron temperature, and position angle have ranges \theta=59+/-9deg, T_e=(3.4+1.2/-0.9)*10^{10}K, and PA=96+/-30deg with 90% confidence. The total range of accretion rate is large, but assuming spin a=0.9 we get \dot{M}(0.9)=(13+4/-3)*10^{-9}M_sun/year interval with 90% confidence. The emission region sizes at 230GHz of the best-fitting models are found to be marginally consistent with the observed by VLBI technique.

by Alexander, Tal
Invited overview lecture in “The Galactic Center, a window to the nuclear environment of disk galaxies” (Shanghai 19-23/10/2009). To appear in ASP Conf. Proc. Ser. “Galactic center workshop 2009″ ed. Mark Morris (12 pp 5 fig)

I discuss four key questions about Galactic Center dynamics, their implications for understanding both the environment of the Galactic MBH and galactic nuclei in general, and the progress made in addressing them. The questions are (1) Is the stellar system around the MBH relaxed? (2) Is there a “dark cusp” around the MBH? (3) What is the origin of the stellar disk(s)?, and (4) What is the origin of the S-stars?

by Dauser, T. and Wilms, J. and Reynolds, C. S. and Brenneman, L. W.
7 pages, 6 figures; accepted by MNRAS for Publication

We present an extended scheme for the calculation of the profiles of emission lines from accretion discs around rotating black holes. The scheme includes discs with angular momenta which are parallel and antiparallel with respect to the black hole’s angular momentum, as both configurations are assumed to be stable (King et al., 2005). We discuss line shapes for such discs and present a code for modelling observational data with this scheme in X-ray data analysis programs. Based on a Green’s function approach, an arbitrary radius dependence of the disc emissivity and arbitrary limb darkening laws can be easily taken into account, while the amount of precomputed data is significantly reduced with respect to other available models.

by Cornish, Neil J.
4 pages, no figures

Theoretical studies in gravitational wave astronomy often require the calculation of Fisher Information Matrices and Likelihood functions, which in a direct approach entail the costly step of computing gravitational waveforms. Here I describe an alternative technique that sidesteps the need to compute full waveforms, resulting in significant computational savings. I describe how related techniques can be used to speed up Bayesian inference applied to real gravitational wave data.

by Noyola, Eva and Gebhardt, Karl and Kissler-Patig, Markus and Lutzgendorf, Nora and Jalali, Behrang and de Zeeuw, P. Tim and Baumgardt, Holger
5 pages, published in The Astrophysical Journal Letters

The Galactic globular cluster omega Centauri is a prime candidate for hosting an intermediate mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT-FLAMES to obtain new integrated spectra for the central region of omega Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. The data support previous measurements performed for a smaller field of view and show a discrepancy with the results from a large proper motion data set. We see a rise in the radial velocity dispersion in the central region to 22.8+-1.2 km/s, which provides a strong sign for a central black hole. Isotropic dynamical models for omega Centauri imply black hole masses ranging from 3.0 to 5.2×10^4 solar masses depending on the center. The best-fitted mass is 4.7+-1.0×10^4 solar masses.

by Hannam, Mark and Husa, Sascha and Ohme, Frank and Mueller, Doreen and Bruegmann, Bernd
20 pages, 9 figures, 6 tables

We present gravitational waveforms for the last orbits and merger of black-hole-binary (BBH) systems along two branches of the BBH parameter space: equal-mass binaries with equal non-precessing spins, and nonspinning unequal-mass binaries. The waveforms are calculated from numerical solutions of Einstein’s equations for black-hole binaries that complete between six and ten orbits before merger. Along the equal-mass spinning branch, the spin parameter of each BH is $latex \chi_i = S_i/M_i^2 \in [-0.85,0.85]$, and along the unequal-mass branch the mass ratio is $latex q =M_2/M_1 \in [1,4]$. We discuss the construction of low-eccentricity puncture initial data for these cases, the properties of the final merged BH, and compare the last 8-10 GW cycles up to $latex M\omega = 0.1$ with the phase and amplitude predicted by standard post-Newtonian (PN) approximants. As in previous studies, we find that the phase from the 3.5PN TaylorT4 approximant is most accurate for nonspinning binaries. For equal-mass spinning binaries the 3.5PN TaylorT1 approximant (including spin terms up to only 2.5PN order) gives the most robust performance, but it is possible to treat TaylorT4 in such a way that it gives the best accuracy for spins $latex \chi_i > -0.75$. When high-order amplitude corrections are included, the PN amplitude of the $latex (\ell=2,m=\pm2)$ modes is larger than the NR amplitude by between 2-4%.

by Burko, Lior M. and Hughes, Scott A.
5 pages, no figures, submitted to Phys. Rev. D

The goal of much research in relativity is to understand gravitational waves generated by a strong-field dynamical spacetime. Quantities of particular interest for many calculations are the Weyl scalar $latex \psi_4$, which is simply related to the flux of gravitational waves far from the source, and the flux of energy carried to distant observers, $latex \dot E$. Conservation laws guarantee that, in asympotically flat spacetimes, $latex \psi_4 \propto 1/r$ and $latex \dot E \propto 1/r^2$ as $latex r \to \infty$. Most calculations extract these quantities at some finite extraction radius. An understanding of finite radius corrections to $latex \psi_4$ and $latex \dot E$ allows us to more accurately infer their asymptotic values from a computation. In this paper, we show that, if the final state of the system is a black hole, then the leading correction to $latex \psi_4$ is $latex {\cal O}(1/r^3)$, and that to the energy flux is $latex {\cal O}(1/r^4)$ — not $latex {\cal O}(1/r^2)$ and $latex {\cal O}(1/r^3)$ as one might naively guess. Our argument only relies on the behavior of the curvature scalars for black hole spacetimes. Using black hole perturbation theory, we calculate the corrections to the leading falloff, showing that it is quite easy to correct for finite extraction radius effects.

by Haiman, Zoltán
10 pages, 5 figures. Review contribution to the Proceedings of “The First Stars and Galaxies: Challenges for the Next Decade”, Austin, TX, March 8-11, 2010

Supermassive black holes (SMBHs) are common in local galactic nuclei, and SMBHs as massive as several billion solar masses already exist at redshift z=6. These earliest SMBHs may arise by the combination of Eddington-limited growth and mergers of stellar-mass seed BHs left behind by the first generation of metal-free stars, or by the rapid direct collapse of gas in rare special environments where the gas can avoid fragmenting into stars. In this contribution, I review these two competing scenarios. I also briefly mention some more exotic ideas and how the different models may be distinguished in the future by LISA and other instruments.

by Wang, J. -M. and Yan, C. -S. and Gao, H. -Q. and Hu, C. and Li, Y. -R. and Zhang, S.
emulateapj.sty, 5 page, 4 figures (in press)

Self-gravitating accretion disks collapse to star-forming(SF) regions extending to the inner edge of the dusty torus in active galactic nuclei (AGNs). A full set of equations including feedback of star formation is given to describe the dynamics of the regions. We explore the role of supernovae explosion (SNexp), acting to excite turbulent viscosity, in the transportation of angular momentum in the regions within 1pc scale. We find that accretion disks with typical rates in AGNs can be driven by SNexp in the regions and metals are produced spontaneously. The present model predicts a metallicity–luminosity relationship consistent with that observed in AGNs. As relics of SF regions, a ring (or belt) consisting of old stars remains for every episode of supermassive black hole activity. We suggest that multiple stellar rings with random directions interact and form a nuclear star cluster after episodes driven by star formation.

by Komorowski, P. G. and Valluri, S. R. and Houde, M.
48 pages, 7 figures, submitted to Classical and Quantum Gravity on March 2nd, 2010

In an extreme binary black hole system, an orbit will increase its angle of inclination (i) as it evolves in Kerr spacetime. We focus our attention on the behaviour of the Carter constant (Q) for near-polar orbits; and develop an analysis that is independent of and complements radiation reaction models. For a Schwarzschild black hole, the polar orbits represent the abutment between the prograde and retrograde orbits at which Q is at its maximum value for given values of latus rectum (l) and eccentricity (e). The introduction of spin (S = |J|/M2) to the massive black hole causes this boundary, or abutment, to be moved towards greater orbital inclination; thus it no longer cleanly separates prograde and retrograde orbits. To characterise the abutment of a Kerr black hole (KBH), we first investigated the last stable orbit (LSO) of a test-particle about a KBH, and then extended this work to general orbits. To develop a better understanding of the evolution of Q we developed analytical formulae for Q in terms of l, e, and S to describe elliptical orbits at the abutment, polar orbits, and last stable orbits (LSO). By knowing the analytical form of dQ/dl at the abutment, we were able to test a 2PN flux equation for Q. We also used these formulae to numerically calculate the di/dl of hypothetical circular orbits that evolve along the abutment. From these values we have determined that di/dl = -(122.7S – 36S^3)l^-11/2 -(63/2 S + 35/4 S^3) l^-9/2 -15/2 S l^-7/2 -9/2 S l^-5/2. Thus the abutment becomes an important analytical and numerical laboratory for studying the evolution of Q and i in Kerr spacetime and for testing current and future radiation back-reaction models for near-polar retrograde orbits.

by Graham, Alister W. and Onken, Christopher A. and Athanassoula, E. and Combes, Francoise
17 pages. Submitted to MNRAS on July 19

[Abridged] We present an updated and improved M_bh-sigma diagram containing 64 galaxies for which M_bh measurements (not just upper limits) are available. Due to new and increased black hole masses at the high-mass end, and a better representation of barred galaxies at the low-mass end, the “classical” (all morphological type) M_bh-sigma relation for predicting black hole masses is log(M_bh/M_Sun) = (5.13+/-0.34)log[sigma/200] + (8.13+/-0.05), with an rms scatter of 0.43 dex. Modifying the regression analysis to correct for a hitherto over-looked sample bias in which black holes with masses <10^6 M_Sun are not (yet) detectable, the relation steepens further to give log(M_bh/M_Sun) = (5.95+/-0.44)log[sigma/200] + (8.15+/-0.06). We have also updated the “barless'' and “elliptical-only'' M_bh-sigma relations introduced by Graham and Hu in 2008 due to the offset nature of barred/disc galaxies. These relations have a total scatter as low as 0.34 dex and currently define the upper envelope of points in the M_bh-sigma diagram. These relations also have a slope consistent with the value 5, in agreement with the prediction by Silk & Rees based on feedback from massive black holes in bulges built by monolithic-collapse.

Using updated virial products and velocity dispersions from 28 active galactic nuclei, we determine that the optimal scaling factor f – which brings their virial products in line with the 64 directly measured black hole masses – is 2.8^{+0.7}_{-0.5}. This is roughly half the value reported by Onken et al. and Woo et al., and consequently halves the mass estimates of most high-redshift quasars. We have explored the results after separating the samples into barred and non-barred galaxies, and we have also developed a preliminary corrective term to the velocity dispersion based on bar dynamics.

by Decarli, Roberto and Dotti, Massimo and Montuori, Carmen and Liimets, Tiina and Ederoclite, Alessandro
2 figures, 1 table. Accepted for publication in ApJ Letters

We report the discovery of peculiar features in the optical spectrum of 4C+22.25, a flat spectrum radio quasar at z=0.4183 observed in the SDSS and in a dedicated spectroscopic follow-up from the Nordic Optical Telescope. The Hbeta and Halpha lines show broad profiles (FWHM~12,000 km/s), faint fluxes and extreme offsets (Delta v=8,700+/-1,300 km/s) with respect to the narrow emission lines. These features show no significant variation in a time lag of ~3.1 yr (rest frame). We rule out possible interpretations based on the superposition of two sources or on recoiling black holes, and we discuss the virtues and limitations of a massive black hole binary scenario.

by Greene, J. E. and Peng, C. Y. and Kim, M. and Kuo, C. Y. and Braatz, J. A. and Impellizzeri, C. M. V. and Condon, J. J. and Lo, K. Y. and Henkel, C. and Reid, M. J.
21 pages, 14 figures, accepted for publication in the Astrophysical Journal

The black hole (BH)-bulge correlations have greatly influenced the last decade of effort to understand galaxy evolution. Current knowledge of these correlations is limited predominantly to high BH masses (M_BH> 10^8 M_sun) that can be measured using direct stellar, gas, and maser kinematics. These objects, however, do not represent the demographics of more typical L< L* galaxies. This study transcends prior limitations to probe BHs that are an order of magnitude lower in mass, using BH mass measurements derived from the dynamics of H_2O megamasers in circumnuclear disks. The masers trace the Keplerian rotation of circumnuclear molecular disks starting at radii of a few tenths of a pc from the central BH. Modeling of the rotation curves, presented by Kuo et al. (2010), yields BH masses with exquisite precision. We present stellar velocity dispersion measurements for a sample of nine megamaser disk galaxies based on long-slit observations using the B&C spectrograph on the Dupont telescope and the DIS spectrograph on the 3.5m telescope at Apache Point. We also perform bulge-to-disk decomposition of a subset of five of these galaxies with SDSS imaging. The maser galaxies as a group fall below the M_BH-sigma* relation defined by elliptical galaxies. We show, now with very precise BH mass measurements, that the low-scatter power-law relation between M_BH and sigma* seen in elliptical galaxies is not universal. The elliptical galaxy M_BH-sigma* relation cannot be used to derive the BH mass function at low mass or the zeropoint for active BH masses. The processes (perhaps BH self-regulation or minor merging) that operate at higher mass have not effectively established an M_BH-sigma* relation in this low-mass regime.

by Blanchet, Luc and Detweiler, Steven and Tiec, Alexandre Le and Whiting, Bernard F.
29 pages, 3 figures; to appear in the book “Mass and Motion in General Relativity”, proceedings of the C.N.R.S. School in Orleans, France, eds. L. Blanchet, A. Spallicci and B. F. Whiting

The relativistic motion of a compact binary system moving in circular orbit is investigated using the post-Newtonian (PN) approximation and the perturbative self-force (SF) formalism. A particular gauge-invariant observable quantity is computed as a function of the binary’s orbital frequency. The conservative effect induced by the gravitational SF is obtained numerically with high precision, and compared to the PN prediction developed to high order. The PN calculation involves the computation of the 3PN regularized metric at the location of the particle. Its divergent self-field is regularized by means of dimensional regularization. The poles proportional to 1/(d-3) which occur within dimensional regularization at the 3PN order disappear from the final gauge-invariant result. The leading 4PN and next-to-leading 5PN conservative logarithmic contributions originating from gravitational-wave tails are also obtained. Making use of these exact PN results, some previously unknown PN coefficients are measured up to the very high 7PN order by fitting to the numerical self-force data. Using just the 2PN and new logarithmic terms, the value of the 3PN coefficient is also confirmed numerically with very high precision. The consistency of this cross-cultural comparison provides a crucial test of the very different regularization methods used in both SF and PN formalisms, and illustrates the complementarity of these approximation schemes when modelling compact binary systems.

by Garfinkle, David and Pretorius, Frans and Yunes, Nicolas
4 pages, no figures, submitted to Rapid Communications

We perform a linear stability analysis of dynamical Chern-Simons modified gravity in the geometric optics approximation and find that it is linearly stable on the backgrounds considered. Our analysis also reveals that gravitational waves in the modified theory travel at the speed of light in Minkowski spacetime. However, on a Schwarzschild background the characteristic speed of propagation along a given direction splits into two modes, one subluminal and one superluminal. The width of the splitting depends on the azimuthal components of the propagation vector, is linearly proportional to the mass of the black hole, and decreases with the third inverse power of the distance from the black hole. Radial propagation is unaffected, implying that as probed by gravitational waves the location of the event horizon of the spacetime is unaltered. The analysis further reveals that when a high frequency, pure gravitational wave is scattered from a black hole, a scalar wave of comparable amplitude is excited, and vice-versa.

by Nichols, David A. and Chen, Yanbei
13 pages, 6 figures, 1 table, revtex4 format

Black-hole-binary coalescence is often divided into three stages: inspiral, merger and ringdown. The post-Newtonian (PN) approximation treats the inspiral phase, black-hole perturbation (BHP) theory describes the ringdown, and the nonlinear dynamics of spacetime characterize the merger. In this paper, we introduce a hybrid method that incorporates elements of PN and BHP theories, and we apply it to the head-on collision of black holes with transverse, anti-parallel spins. We compare our approximation technique with a full numerical-relativity simulation, and we find good agreement between the gravitational waveforms and the radiated energy and momentum. Our results suggest that PN and BHP theories may suffice to explain the main features of outgoing gravitational radiation for head-on mergers. This would further imply that linear perturbations to exact black-hole solutions can capture the nonlinear aspects of head-on binary-black-hole mergers accessible to observers far from the collision.

by Angelil, Raymond and Saha, Prasenjit and Merritt, David
20 pages, 9 figures, submitted to the ApJ

The S stars orbiting the Galactic center black hole reach speeds of up to a few percent the speed of light during pericenter passage. This makes, for example, S2 at pericenter much more relativistic than known binary pulsars, and opens up new possibilities for testing general relativity. This paper develops a technique for fitting nearly-Keplerian orbits with perturbations from Schwarzschild curvature, frame dragging, and spin-induced torque, to redshift measurements distributed along the orbit but concentrated around pericenter. Both orbital and light-path effects are taken into account. It turns out that absolute calibration of rest-frame frequency is not required. Hence, if pulsars on orbits similar to the S stars are discovered, the technique described here can be applied without change, allowing the much greater accuracies of pulsar timing to be taken advantage of. For example, pulse timing of 3 microsec over one hour amounts to an effective redshift precision of 30 cm/s, enough to measure frame dragging and the quadrupole moment from an S2-like orbit, provided problems like the Newtonian “foreground” due to other masses can be overcome. On the other hand, if stars with orbital periods of order a month are discovered, the same could be accomplished with stellar spectroscopy from the E-ELT at the level of 1 km/s.

by Key, Joey Shapiro and Cornish, Neil J.
11 pages, 19 figures

The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can provide strong constraints on theories of galaxy mergers in the early universe.

by Gualandris, Alessia and Gillessen, Stefan and Merritt, David
8 pages, 11 figures, submitted to MNRAS

We study the short-term effects of an intermediate mass black hole (IBH) on the orbit of star S2 (S02), the shortest period star known to orbit the supermassive black hole (SBH) in the centre of the Milky Way. Near-infrared imaging and spectroscopic observations allow an accurate determination of the orbit of the star. Given S2’s short orbital period and large eccentricity, general relativity (GR) needs to be taken into account, and its effects are potentially measurable with current technology. We show that perturbations due to an IBH in orbit around the SBH can produce a shift in the apoapsis of S2 that is as large or even larger than the GR shift. An IBH will also induce changes in the plane of S2’s orbit at a level as large as one degree per period. We apply observational orbital fitting techniques to simulations of the S-cluster in the presence of an IBH and find that an IBH more massive than about 1000 solar masses at the distance of the S-stars will be detectable at the next periapse passage of S2, which will occur in 2018.

by Kelly, Brandon C. and Vestergaard, Marianne and Fan, Xiaohui and Hopkins, Philip and Hernquist, Lars and Siemiginowska, Aneta
Accepted by ApJ, 25 pages (emulateapj), 11 figures

We present an estimate of the black hole mass function (BHMF) of broad line quasars (BLQSOs) that self-consistently corrects for incompleteness and the statistical uncertainty in the mass estimates, based on a sample of 9886 quasars at 1 < z 1 it is highly incomplete at M_BH < 10^9 M_Sun and L / L_Edd 1, where the BLQSO phase occurs at the end of a fueling event when black hole feedback unbinds the accreting gas, halting the accretion flow.

by Thornburg, Jonathan
27 pages, 12 eps figures (10 of them color, but all are viewable ok in black-and-white), uses RevTeX 4.1

If a small “particle” of mass $latex \mu M$ (with $latex \mu \ll 1$) orbits a Schwarzschild or Kerr black hole of mass $latex M$, the particle is subject to an $latex \O(\mu)$ radiation-reaction “self-force”. Here I argue that it’s valuable to compute this self-force highly accurately (relative error of $latex \ltsim 10^{-6}$) and efficiently, and I describe techniques for doing this and for obtaining and validating error estimates for the computation. I use an adaptive-mesh-refinement (AMR) time-domain numerical integration of the perturbation equations in the Barack-Ori mode-sum regularization formalism; this is efficient, yet allows easy generalization to arbitrary particle orbits. I focus on the model problem of a scalar particle in a circular geodesic orbit in Schwarzschild spacetime.

The mode-sum formalism gives the self-force as an infinite sum of regularized spherical-harmonic modes $latex \sum_{\ell=0}^\infty F_{\ell,\reg}$, with $latex F_{\ell,\reg}$ (and an “internal” error estimate) computed numerically for $latex \ell \ltsim 30$ and estimated for larger~$latex \ell$ by fitting an asymptotic “tail” series. Here I validate the internal error estimates for the individual $latex F_{\ell,\reg}$ using a large set of numerical self-force computations of widely-varying accuracies. I present numerical evidence that the actual numerical errors in $latex F_{\ell,\reg}$ for different~$latex \ell$ are at most weakly correlated, so the usual statistical error estimates are valid for computing the self-force. I show that the tail fit is numerically ill-conditioned, but this can be mostly alleviated by renormalizing the basis functions to have similar magnitudes.

Using AMR, fixed mesh refinement, and extended-precision floating-point arithmetic, I obtain the (contravariant) radial component of the self-force for a particle in a circular geodesic orbit of areal radius $latex r = 10M$ to within $latex 1$~ppm relative error.

by Tessmer, Manuel and Schaefer, Gerhard
28 pages

The article provides ready-to-use 1pN-accurate frequency-domain gravitational wave forms for eccentric nonspinning compact binaries of arbitrary mass ratio including the first post-Newtonian (1pN) point particle corrections to the far-zone gravitational wave amplitude, given in terms of tensor spherical harmonics. The averaged equations for the decay of the eccentricity and growth of radial frequency due to radiation reaction are used to provide stationary phase approximations to the frequency-domain wave forms.

by Fu, Wen and Lai, Dong
15 pages, 10 figures, submitted to MNRAS

Hot accretion tori around a compact object are known to be susceptible to a global hydrodynamical instability, the so-called Papaloizou-Pringle (PP) instability, arising from the interaction of non-axisymmetric waves across the corotation radius, where the wave pattern speed matches the fluid rotation rate. However, accretion tori produced in various astrophysical situations (e.g., collapsars and neutron star binary mergers) are likely to be highly magnetized. We study the effect of magnetic fields on the PP instability in incompressible tori with various magnetic strengths and structures. In general, toroidal magnetic fields have significant effects on the PP instability: For thin tori (with the fractional width relative to the outer torus radius much less than unity), the instability is suppressed at large field strengths with the corresponding toroidal Alfven speed $latex v_{A\phi}\go 0.2r\Omega$ (where $latex \Omega$ is the flow rotation rate). For thicker tori (with the fractional width of order 0.4 or larger), which are hydrodynamically stable, the instability sets in for sufficiently strong magnetic fields (with $latex v_{A\phi}\go 0.2 r\Omega$). Our results suggest that highly magnetized accretion tori may be subjected to global instability even when it is stable against the usual magneto-rotational instability.

by Park, KwangHo and Ricotti, Massimo
14 pages, 12 figures, submitted to ApJ

We study the effect of radiative feedback on accretion onto intermediate mass black holes (IMBHs) using the hydrodynamical code ZEUS-MP with a radiative transfer algorithm. In this paper, the first of a series, we assume accretion from a uniformly dense gas with zero angular momentum. Our 1D and 2D simulations explore how X-ray and UV radiation emitted near the black hole regulates the gas supply from large scales. Both 1D and 2D simulations show similar accretion rate and period between peaks in accretion, meaning that the hydro-instabilities that develop in 2D simulations do not affect the mean flow properties. We present a suite of simulations exploring accretion across a large parameter space, including different radiative efficiencies and radiation spectra, black hole masses, density and temperature, $latex T_\infty$, of the neighboring gas. In agreement with previous studies we find regular oscillatory behavior of the accretion rate, with duty cycle $latex \sim 7%$, mean accretion rate 3-6% $latex (T_{\infty}/10^4 {\rm K})^{2.5}$ of the Bondi rate and peak accretion $latex \sim 10$ times the mean. We derive parametric formulas for the period between bursts, the mean accretion rate and the peak luminosity of the bursts and thus provide a formulation of how feedback regulated accretion operates. The temperature profile of the hot ionized gas is crucial in determining the accretion rate, while the period of the bursts is proportional to the mean size of the Str\”{o}mgren sphere. We also find that softer spectrum of radiation produces higher accretion rate. This study is a first step to model the growth of seed black holes in the early universe and to make a prediction of the number and the luminosity of ultra-luminous X-ray sources in galaxies produced by IMBHs accreting from the interstellar medium.

by Schneider, Justus and Amaro-Seoane, Pau and Spurzem, Rainer
Submitted to MNRAS, comments welcome

Dense stellar systems such as globular clusters, galactic nuclei and nuclear star clusters are ideal loci to study stellar dynamics due to the very high densities reached, usually a million times higher than in the solar neighborhood; they are unique laboratories to study processes related to relaxation. There are a number of different techniques to model the global evolution of such a system. In statistical models we assume that relaxation is the result of a large number of two-body gravitational encounters with a net local effect. We present two moment models that are based on the collisional Boltzmann equation. By taking moments of the Boltzmann equation one obtains an infinite set of differential moment equations where the equation for the moment of order $latex n$ contains moments of order $latex n+1$. In our models we assume spherical symmetry but we do not require dynamical equilibrium. We truncate the infinite set of moment equations at order $latex n=4$ for the first model and at order $latex n=5$ for the second model. The collisional terms on the right-hand side of the moment equations account for two-body relaxation and are computed by means of the Rosenbluth potentials. We complete the set of moment equations with closure relations which constrain the degree of anisotropy of our model by expressing moments of order $latex n+1$ by moments of order $latex n$. The accuracy of this approach relies on the number of moments included from the infinite series. Since both models include fourth order moments we can study mechanisms in more detail that increase or decrease the number of high velocity stars. The resulting model allows us to derive a velocity distribution function, with unprecedented accuracy, compared to previous moment models.

by Robinson, Andrew and Young, Stuart and Axon, David J. and Kharb, Preeti and Smith, James E.
18 pages, 4 figures, accepted for publication in the Astrophysical Journal as a Letter

We report spectropolarimetric observations of the quasar E1821+643 (z=0.297), which suggest that it may be an example of gravitational recoil due to anisotropic emission of gravitational waves following the merger of a supermassive black hole (SMBH) binary. In total flux, the broad Balmer lines are redshifted by ~1000 km/s relative to the narrow lines and have highly red asymmetric profiles, whereas in polarized flux the broad H_alpha line exhibits a blueshift of similar magnitude and a strong blue asymmetry. We show that these observations are consistent with a scattering model in which the broad-line region has two components, moving with different bulk velocities away from the observer and towards a scattering region at rest in the host galaxy. If the high velocity system is identified as gas bound to the SMBH, this implies that the SMBH is itself moving with a velocity ~2100 km/s relative to the host galaxy. We discuss some implications of the recoil hypothesis and also briefly consider whether our observations can be explained in terms of scattering of broad-line emission originating from the active component of an SMBH binary, or from an outflowing wind.

by Sesana, A.
15 pages, 9 figures, accepted for publication in the Astrophysical Journal

We construct evolutionary tracks for massive black hole binaries (MBHBs) embedded in a surrounding distribution of stars. The dynamics of the binary is evolved by taking into account the erosion of the central stellar cusp bound to the massive black holes, the scattering of unbound stars feeding the binary loss cone, and the emission of gravitational waves (GWs). Stellar dynamics is treated in a hybrid fashion by coupling the results of numerical 3-body scattering experiments of bound and unbound stars to an analytical framework for the evolution of the stellar density distribution and for the efficiency of the binary loss cone refilling. Our main focus is on the behaviour of the binary eccentricity, in the attempt of addressing its importance in the merger process and its possible impact for GW detection with the planned Laser Interferometer Space Antenna ({\it LISA}), and ongoing and forthcoming pulsar timing array (PTA) campaigns. We produce a family of evolutionary tracks extensively sampling the relevant parameters of the system which are the binary mass, mass ratio and initial eccentricity, the slope of the stellar density distribution, its normalization and the efficiency of loss cone refilling. We find that, in general, stellar dynamics causes a dramatic increase of the MBHB eccentricity, especially for initially already mildly eccentric and/or unequal mass binaries. When applied to standard MBHB population models, our results predict eccentricities in the ranges $latex 10^{-3}-0.2$ and $latex 0.03-0.3$ for sources detectable by {\it LISA} and PTA respectively. Such figures may have a significant impact on the signal modelling, on source detection, and on the development of parameter estimation algorithms.

by Konstantinidis, Simos and Kokkotas, Kostas D.
24 pages, 28 figures

We present a new C++ code for collisional N-body simulations of star clusters. The code uses the Hermite fourth-order scheme with block time steps, for advancing the particles in time, while the forces and neighboring particles are computed using the GRAPE-6 board. Special treatment is used for close encounters, binary and multiple sub-systems that either form dynamically or exist in the initial configuration. The structure of the code is modular and allows the appropriate treatment of more physical phenomena, such as stellar and binary evolution, stellar collisions and evolution of close black-hole binaries. Moreover, it can be easily modified so that the part of the code that uses GRAPE-6, could be replaced by another module that uses other accelerating-hardware like the Graphics Processing Units (GPUs). Appropriate choice of the free parameters give a good accuracy and speed for simulations of star clusters up to and beyond core collapse. Simulations of Plummer models consisting of equal-mass stars reached core collapse at t~17 half-mass relaxation times, which compares very well with existing results, while the cumulative relative error in the energy remained below 0.001. Also, comparisons with published results of other codes for the time of core collapse for different initial conditions, show excellent agreement. Simulations of King models with an initial mass-function, similar to those found in the literature, reached core collapse at t~0.17, which is slightly smaller than the expected result from previous works. Finally, the code accuracy becomes comparable and even better than the accuracy of existing codes, when a number of close binary systems is dynamically created in a simulation. This is due to the high accuracy of the method that is used for close binary and multiple sub-systems.

by Galley, Chad R. and Herrmann, Frank and Silberholz, John and Tiglio, Manuel and Guerberoff, Gustavo

We perform a statistical analysis of the binary black hole problem in the post-Newtonian approximation by systematically sampling and evolving the parameter space of initial configurations for quasi-circular inspirals. Through a principal component analysis of spin and orbital angular momentum variables we systematically look for uncorrelated quantities and find three of them which are highly conserved in a statistical sense, both as functions of time and with respect to variations in initial spin orientations. We also look for and find the variables that account for the largest variations in the problem. We present binary black hole simulations of the full Einstein equations analyzing to what extent these results might carry over to the full theory in the inspiral and merger regimes. Among other applications these results should be useful both in semi-analytical and numerical building of templates of gravitational waves for gravitational wave detectors.

by Schnittman, Jeremy D.
10 pages, 4 figures, submitted to ApJ; comments welcome

We calculate the location and stability of the L_4 and L_5 Lagrange equilibrium points in the circular restricted three-body problem as the binary system evolves via gravitational radiation losses. Relative to the purely Newtonian case, we find that the L_4 equilibrium point moves towards the secondary mass and becomes slightly less stable, while the L_5 point moves away from the secondary and gains in stability. We discuss a number of astrophysical applications of these results, in particular as a mechanism for producing electromagnetic counterparts to gravitational-wave signals.

by Genzel, Reinhard and Eisenhauer, Frank and Gillessen, Stefan
submitted to Rev.Mod.Phys.,comments are welcome

The Galactic Center is an excellent laboratory for studying phenomena and physical occurring in many other galactic nuclei. The Center of our Milky Way is by far the closest galactic nucleus, and observations with exquisite resolution and sensitivity cover 18 orders of magnitude in energy of electromagnetic radiation. Theoretical simulations have become increasingly more powerful in explaining these measurements. This review summarizes the recent progress in observational and theoretical work on the central parsec, with a strong emphasis on the current empirical evidence for a central massive black hole and on the properties of the surrounding dense star cluster. We present the current evidence, from the analysis of the orbits of more than two dozen stars and from the measurements of the size and motion of the central compact radio source, Sgr A*, that this radio source must be a massive black hole of about 4.4 x 106 M_\odot, beyond any reasonable doubt. We report what is known about the structure and evolution of the dense nuclear star cluster surrounding this black hole, including the astounding fact that stars have been forming in the vicinity of Sgr A* recently, apparently with a top-heavy stellar mass function. We discuss a dense concentration of fainter stars centered in the immediate vicinity of the massive black hole, three of which have orbital peri-bothroi of less than one light day. This ‘S-star cluster’ appears to consist mainly of young early-type stars, in contrast to the predicted properties of an equilibrium ’stellar cusp’ around a black hole. This constitutes a remarkable and presently not fully understood ‘paradox of youth’. We also summarize more briefly what is known about the emission properties of the accreting gas onto Sgr A* and how this emission is beginning to delineate the physical properties in the hot accretion zone around the event horizon.

by Kocsis, Bence and Tremaine, Scott
16 pages, 8 figures, submitted to MNRAS

Observations of the spatial distribution and kinematics of young stars in the Galactic centre can be interpreted as showing that the stars occupy one, or possibly two, discs of radii ~0.05-0.5 pc. The most prominent (`clockwise’) disc exhibits a strong warp: the normals to the mean orbital planes in the inner and outer third of the disc differ by ~60 deg. Using an analytical model based on Laplace-Lagrange theory, we show that such warps arise naturally and inevitably through vector resonant relaxation between the disc and the surrounding old stellar cluster.

by Porto, Rafael A.
25 pages, 4 figures, revtex4

Using effective field theory (EFT) techniques we calculate the next-to-leading order (NLO) spin-orbit contributions to the gravitational potential of inspiralling compact binaries. We use the covariant spin supplementarity condition (SSC), and explicitly prove the equivalence with previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the direct application of the Newton-Wigner SSC at the level of the action leads to the correct dynamics using a canonical (Dirac) algebra. This paper then completes the calculation of the necessary spin dynamics within the EFT formalism that will be used in a separate paper to compute the spin contributions to the energy flux and phase evolution to NLO.

by Schutz, Bernard F and Ricci, Franco
82 pages, 9 figures, lecture notes from 1999, not posted to ArXiV at the time because they exceeded the article/figure size limits

Notes of lectures for graduate students that were given at Lake Como in 1999, covering the theory of linearized gravitational waves, their sources, and the prospects at the time for detecting gravitational waves. The lectures remain of interest for pedagogical reasons, and in particular because they contain a treatment of current-quadrupole gravitational radiation (in connection with the r-modes of neutron stars) that is not readily available in other sources.

by Molina, C. and Pani, Paolo and Cardoso, Vitor and Gualtieri, Leonardo
RevTex4, 12 pages, 8 figures, 3 Tables

Dynamical Chern-Simons gravity is an extension of General Relativity in which the gravitational field is coupled to a scalar field through a parity-violating Chern-Simons term. In this framework, we study perturbations of spherically symmetric black hole spacetimes, assuming that the background scalar field vanishes. Our results suggest that these spacetimes are stable, and small perturbations die away as a ringdown. However, in contrast to standard General Relativity, the gravitational waveforms are also driven by the scalar field. Thus, the gravitational oscillation modes of black holes carry imprints of the coupling to the scalar field. This is a smoking gun for Chern-Simons theory and could be tested with gravitational-wave detectors, such as LIGO or LISA. For negative values of the coupling constant, ghosts are known to arise, and we explicitly verify their appearance numerically. Our results are validated using both time evolution and frequency domain methods.

by Colaiuda, A. and Ferrari, V. and Gualtieri, L. and Pons, J. A.
25 pages, 9 figures, submitted to MNRAS

We find numerical solutions of the coupled system of Einstein-Maxwell’s equations with a linear approach, in which the magnetic field acts as a perturbation of a spherical neutron star. In our study, magnetic fields having both poloidal and toroidal components are considered, and higher order multipoles are also included. We evaluate the deformations induced by different field configurations, paying special attention to those for which the star has a prolate shape. We also explore the dependence of the stellar deformation on the particular choice of the equation of state and on the mass of the star. Our results show that, for neutron stars with mass M = 1.4 Msun and surface magnetic fields of the order of 10^15 G, a quadrupole ellipticity of the order of 10^(-6) – 10^(-5) should be expected. Low mass neutron stars are in principle subject to larger deformations (quadrupole ellipticities up to 10^(-3) in the most extreme case). The effect of quadrupolar magnetic fields is comparable to that of dipolar components. A magnetic field permeating the whole star is normally needed to obtain negative quadrupole ellipticities, while fields confined to the crust typically produce positive quadrupole ellipticities.

by Schneider, Raffaella and Marassi, Stefania and Ferrari, Valeria
10 pages, 9 figures, proceedings of the GWDAW 10 Conference, submitted to Class. & Quantum Grav

Astrophysical sources emit gravitational waves in a large variety of processes occurred since the beginning of star and galaxy formation. These waves permeate our high redshift Universe, and form a background which is the result of the superposition of different components, each associated to a specific astrophysical process. Each component has different spectral properties and features that it is important to investigate in view of a possible, future detection. In this contribution, we will review recent theoretical predictions for backgrounds produced by extragalactic sources and discuss their detectability with current and future gravitational wave observatories.

by Sethi, Shiv K. and Haiman, Zoltán and Pandey, Kanhaiya
submitted to ApJ, 5 emulateapj pages and 5 figures

It has been proposed that primordial gas in early dark matter halos, with virial temperatures above 10^4 K, can avoid fragmentation and undergo rapid collapse, possibly resulting in a supermassive black hole (SMBH). This requires the gas to avoid cooling and to remain at temperatures near T=10^4 K. We show that this condition can be satisfied in the presence of a sufficiently strong primordial magnetic field, which heats the collapsing gas via ambipolar diffusion. If the field has a strength above B = 3.6 (comoving) nG, the collapsing gas is kept warm (T=10^4K) until it reaches the critical density n_crit=10^3 cm^{-3} at which the roto-vibrational states of H_2 approach local thermodynamic equilibrium. H_2-cooling then remains inefficient, and the gas temperature stays near 10^4K, even as it continues to collapse to higher densities. The critical magnetic field strength required to permanently suppress H_2-cooling is somewhat higher than upper limit of approx. 2 nG from the cosmic microwave background (CMB). However, it can be realized in the rare (2-3)-sigma regions of the spatially fluctuating B-field; these regions contain a sufficient number of halos to account for the z=6 quasar BHs.

by Pucacco, Giuseppe and Bassan, Massimo and Visco, Massimo
27pages, 20 figures

We investigate autonomous perturbations on the orbits of LISA, namely the effects produced by fields that can be expressed only in terms of the position, but not of time in the Hill frame. This first step in the study of the LISA orbits has been the subject of recent papers which implement analytical techniques based on a “post-epicyclic” approximation in the Hill frame to find optimal unperturbed orbits. The natural step forward is to analyze the perturbations to purely Keplerian orbits. In the present work a particular emphasis is put on the tidal field of the Earth assumed to be stationary in the Hill frame. An accurate interpretation of the global structure of the perturbed solution sheds light on possible implications on injection in orbit when the time base-line of the mission is longer than that assumed in previous papers. Other relevant classes of autonomous perturbations are those given by the corrections to the Solar field responsible for a slow precession and a global stationary field, associated to sources like the interplanetary dust or a local dark matter component. The inclusion of simple linear contributions in the expansion of these fields produces secular solutions that can be compared with the measurements and possibly used to evaluate some morphological property of the perturbing components.

by Gergely, László Á. and Biermann, Peter L. and Caramete, Laurenţiu I.
11 pages, 2 figures

During post-Newtonian evolution of a compact binary, a mass ratio different from one provides a second small parameter, which can lead to unexpected results. We present a statistics of supermassive black hole candidates, which enables us first to derive their mass distribution, then to establish a logarithmically even probability of the mass ratios at their encounter. In the mass ratio range (1/30,1/3) of supermassive black hole mergers representing 40% of all possible cases, the combined effect of spin-orbit precession and gravitational radiation leads to a spin-flip of the dominant spin during the inspiral phase of the merger. This provides a mechanism for explaining a large set of observations on X-shaped radio galaxies. In another 40%, with mass ratios (1/30,1/1000) a spin-flip never happens, while in the remaining 20% of mergers with mass ratios (1/3,1) it may occur during the plunge. We analyze the magnitude of the spin-flip angle occurring during the inspiral as function of the mass ratio and original relative orientation of the spin and orbital angular momentum. We also derive a formula for the final spin at the end of the inspiral in this mass ratio range.

by de Vine, Glenn and Ware, Brent and McKenzie, Kirk and Spero, Robert E. and Klipstein, William M. and Shaddock, Daniel A.
4 pages, 4 figures, to appear in Physical Review Letters end of May 2010

We report on the first demonstration of time-delay interferometry (TDI) for LISA, the Laser Interferometer Space Antenna. TDI was implemented in a laboratory experiment designed to mimic the noise couplings that will occur in LISA. TDI suppressed laser frequency noise by approximately 10^9 and clock phase noise by 6×10^4, recovering the intrinsic displacement noise floor of our laboratory test bed. This removal of laser frequency noise and clock phase noise in post-processing marks the first experimental validation of the LISA measurement scheme.

by Batcheldor, D. and Robinson, A. and Axon, D. J. and Perlman, E. S. and Merritt, D.
ApJ Letters accepted

Isophotal analysis of M87, using data from the Advanced Camera for Surveys, reveals a projected displacement of 6.8 +/- 0.8 pc (~ 0.1 arcsec) between the nuclear point source (presumed to be the location of the supermassive black hole, SMBH) and the photo-center of the galaxy. The displacement is along a position angle of 307 +/- 17 degrees and is consistent with the jet axis. This suggests the active SMBH in M87 does not currently reside at the galaxy center of mass, but is displaced in the counter-jet direction. Possible explanations for the displacement include orbital motion of an SMBH binary, gravitational perturbations due to massive objects (e.g., globular clusters), acceleration by an asymmetric or intrinsically one-sided jet, and gravitational recoil resulting from the coalescence of an SMBH binary. The displacement direction favors the latter two mechanisms. However, jet asymmetry is only viable, at the observed accretion rate, for a jet age of >0.1 Gyr and if the galaxy restoring force is negligible. This could be the case in the low density core of M87. A moderate recoil ~1 Myr ago might explain the disturbed nature of the nuclear gas disk, could be aligned with the jet axis, and can produce the observed offset. Alternatively, the displacement could be due to residual oscillations resulting from a large recoil that occurred in the aftermath of a major merger any time in the last 10 Gyr.

by Klein, Antoine and Jetzer, Philippe
7 pages, 1 figure; Accepted for publication in Phys. Rev. D

We compute here the spin-orbit and spin-spin couplings needed for an accurate computation of the phasing of gravitational waves emitted by comparable-mass binaries on eccentric orbits at the second post-Newtonian (PN) order. We use a quasi-Keplerian parametrization of the orbit free of divergencies in the zero eccentricity limit. We find that spin-spin couplings induce a residual eccentricity for coalescing binaries at 2PN, of the order of $latex 10^{-4}$-$latex 10^{-3}$ for supermassive black hole binaries in the LISA band. Spin-orbit precession also induces a non-trivial pattern in the evolution of the eccentricity, which could help to reduce the errors on the determination of the eccentricity and spins in a gravitational wave measurement.

by Finn, Lee Samuel and Lommen, Andrea N.
43 pages, 13 figures, submitted to ApJ.

Efforts to detect gravitational waves by timing an array of pulsars have focused traditionally on stationary gravitational waves: e.g., stochastic or periodic signals. Gravitational wave bursts — signals whose duration is much shorter than the observation period — will also arise in the pulsar timing array waveband. Sources that give rise to detectable bursts include the formation or coalescence of supermassive black holes (SMBHs), the periapsis passage of compact objects in highly elliptic or unbound orbits about a SMBH, or cusps on cosmic strings. Here we describe how pulsar timing array data may be analyzed to detect and characterize these bursts. Our analysis addresses, in a mutually consistent manner, a hierarchy of three questions: \emph{i}) What are the odds that a dataset includes the signal from a gravitational wave burst? \emph{ii}) Assuming the presence of a burst, what is the direction to its source? and \emph{iii}) Assuming the burst propagation direction, what is the burst waveform’s time dependence in each of its polarization states? Applying our analysis to synthetic data sets we find that we can \emph{detect} gravitational waves even when the radiation is too weak to either localize the source of infer the waveform, and \emph{detect} and \emph{localize} sources even when the radiation amplitude is too weak to permit the waveform to be determined. While the context of our discussion is gravitational wave detection via pulsar timing arrays, the analysis itself is directly applicable to gravitational wave detection using either ground or space-based detector data.

by Tanaka, Takamitsu and Haiman, Zoltan and Menou, Kristen
27 pages, 5 figures, submitted to ApJ

The coalescence of a supermassive black hole binary (SMBHB) is thought to be accompanied by an electromagnetic (EM) afterglow, produced by the viscous infall of the surrounding circumbinary gas disk after the merger. It has been proposed that once the merger has been detected in gravitational waves (GWs) by LISA, follow-up EM searches for this afterglow can help identify the EM counterpart of the LISA source. Here we study whether the afterglows may be sufficiently bright and numerous to be detectable in EM surveys alone. The viscous afterglow, which lasts for years to decades for SMBHBs in LISA’s sensitivity window, is characterized by rapid increases in both the bolometric luminosity and in the spectral hardness of the source. If quasar activity is triggered by the same major galaxy mergers that produce SMBHBs, then the afterglow could be interpreted as a signature of the birth of a quasar. Using an idealized model for the post-merger viscous spreading of the circumbinary disk and the resulting light curve, and using the observed luminosity function of quasars as a proxy for the SMBHB merger rate, we delineate the survey requirements for identifying such birthing quasars. If circumbinary disks have a high disk surface density and viscosity, an all-sky soft X-ray survey with a sensitivity of ~10%/yr. If >1% of the X-ray emission is reprocessed into optical frequencies, birthing quasars could also be identified in optical transient surveys such as the LSST. Distinguishing a birthing quasar from other variable sources may be facilitated by the monotonic hardening of its spectrum, but will likely remain challenging. This reinforces the notion that joint EM-plus-GW observations offer the best prospects for identifying the EM signatures of SMBHB mergers.

by Cornish, Neil J. and Key, Joey Shapiro
9 pages

Several scenarios have been proposed in which the orbits of binary black holes enter the band of a gravitational wave detector with significant eccentricity. To avoid missing these signals or biasing the parameter estimation it is important that we consider waveform models that account for eccentricity. The ingredients needed to compute post-Newtonian (PN) waveforms produced by spinning black holes inspiralling on quasi-eccentric orbits have been available for almost two decades at 2 PN order, and this work has recently been extended to 2.5 PN order. However, the computational cost of directly implementing these waveforms is high, requiring many steps per orbit to evolve the system of coupled differential equations. Here we employ a separation of timescales and a generalized Keplarian parameterization of the orbits to produce efficient waveforms describing spinning black hole binaries with arbitrary spin orientations on quasi-eccentric orbits to 1.5 PN order. Our solution includes the spin contributions to the decay of the semi-major axis and eccentricity. We outline a scheme for extending our approach to higher post-Newtonian order.

by Hirata, Christopher M. and Holz, Daniel E. and Cutler, Curt
11 pages, 6 figures, to be submitted to PRD

Gravitational wave sources are a promising cosmological standard candle because their intrinsic luminosities are determined by fundamental physics (and are insensitive to dust extinction). They are, however, affected by weak lensing magnification due to the gravitational lensing from structures along the line of sight. This lensing is a source of uncertainty in the distance determination, even in the limit of perfect standard candle measurements. It is commonly believed that the uncertainty in the distance to an ensemble of gravitational wave sources is limited by the standard deviation of the lensing magnification distribution divided by the square root of the number of sources. Here we show that by exploiting the non-Gaussian nature of the lensing magnification distribution, we can improve this distance determination, typically by a factor of 2–3; we provide a fitting formula for the effective distance accuracy as a function of redshift for sources where the lensing noise dominates.

by Bekki, Kenji and Graham, Alister W.
15 page, 5 figures, accepted in ApJL

Giant elliptical galaxies, believed to be built from the merger of lesser galaxies, are known to house a massive black hole at their center rather than a compact star cluster. If low- and intermediate-mass galaxies do indeed partake in the hierarchical merger scenario, then one needs to explain why their dense nuclear star clusters are not preserved in merger events. A valuable clue may the recent revelation that nuclear star clusters and massive black holes frequently co-exist in intermediate mass bulges and elliptical galaxies. In an effort to understand the physical mechanism responsible for the disappearance of nuclear star clusters, we have numerically investigated the evolution of merging star clusters with seed black holes. Using black holes that are 1-5% of their host nuclear cluster mass, we reveal how their binary coalescence during a merger dynamically heats the newly wed star cluster, expanding it, significantly lowering its central stellar density, and thus making it susceptible to tidal destruction during galaxy merging. Moreover, this mechanism provides a pathway to explain the observed reduction in the nucleus-to-galaxy stellar mass ratio as one proceeds from dwarf to giant elliptical galaxies.

by Shang, Cien and Haiman, Zoltan
16 pages, 9 tables, 12 figures, submitted to MNRAS

The gravitational waves (GWs) emitted by inspiraling binary black holes, expected to be detected by the Laser Interferometer Space Antenna (LISA), could be used to determine the luminosity distance to these sources with the unprecedented precision of <~ 1%. We study cosmological parameter constraints from such standard sirens, in the presence of gravitational lensing by large-scale structure. Lensing introduces magnification with a probability distribution function (PDF) whose shape is highly skewed and depends on cosmological parameters. We use Monte-Carlo simulations to generate mock samples of standard sirens, including a small intrinsic scatter, as well as the additional, larger scatter from lensing, in their inferred distances. We derive constraints on cosmological parameters, by simultaneously fitting the mean and the distribution of the residuals on the distance vs redshift (d_L – z) Hubble diagram. We find that for standard sirens at redshift z ~ 1, the sensitivity to a single cosmological parameter, such as the matter density Omega_m, or the dark energy equation of state w, is ~ 50%-80% tighter when the skewed lensing PDF is used, compared to the sensitivity derived from a Gaussian PDF with the same variance. When these two parameters are constrained simultaneously, the skewness yields a further enhanced improvement (by ~ 120%), owing to the correlation between the parameters. The sensitivity to the amplitude of the matter power spectrum, sigma_8 from the cosmological dependence of the PDF alone, however, is ~ 20% worse than that from the Gaussian PDF. At higher redshifts, the PDF resembles a Gaussian more closely, and the effects of the skewness become less prominent. These results highlight the importance of obtaining an accurate and reliable PDF of the lensing convergence, in order to realize the full potential of standard sirens as cosmological probes.

by Silk, Joe and Nusser, Adi

Force balance considerations put a limit on the rate of AGN radiation momentum output, $latex L/c$, capable of driving galactic superwinds. We show that this condition is insufficient: black holes obeying the observed $latex \mbh -\sigma $ relation cannot supply enough energy in radiation which can drive the gas out by pressure alone. The shortfall is by up to an order of magnitude in most, but not all, cases. We propose that outflow-triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost, and suggest possible tests of this hypothesis. We further point out that the time-scales for Bondi accretion and for orbital decay of merging clumps by dynamical friction in the nuclear disk around a central black hole both follow a similar scaling with mass, favoring the most massive black holes, but the latter process is up to two orders of magnitude more rapid at $latex z\gtsim 10.$ The combination of accretion and coalescence results in earlier formation of more massive black holes, and, in particular, can account for the masses of the black holes inferred to power AGN at $latex z\sim 6.$