## [1211.6608] Multiple stellar-mass black holes in globular clusters: theoretical confirmation

Authors: Anna C. Sippel, Jarrod R. Hurley

Date: 28 Nov 2012

Abstract: While tens or hundreds of stellar-remnant black holes are expected to form in globular star clusters, it is still unclear how many of those will be retained upon formation, and how many will be ejected through subsequent dynamical interactions. No such black holes have been found in any Milky Way globular cluster until the recent discovery of stellar-mass black holes in the globular cluster M22 (NGC 6656) with now an estimated population of 5-100 black holes. We present a direct N-body model of a star cluster of the same absolute and dynamical age as M22. Imposing an initial retention fraction of approx. 10% for black holes, 16 stellar-remnant black holes are retained at a cluster age of 12 Gyr, in agreement with the estimate for M22. Of those 16 BHs, two are in a binary system with a main sequence star each while also one pure black hole binary is present. We argue that multiple black holes can be present in any Milky Way cluster with an extended core radius, such as M22 or the model presented here.

#### Nov 30, 2012

1211.6608 (/preprints)
2012-11-30, 21:53 

## [1211.6558] New tests of local Lorentz invariance and local position invariance of gravity with pulsars

Authors: Lijing Shao, Norbert Wex, Michael Kramer

Date: 28 Nov 2012

Abstract: New tests are proposed to constrain possible deviations from local Lorentz invariance and local position invariance in the gravity sector. By using precise timing results of two binary pulsars, i.e., PSRs J1012+5307 and J1738+0333, we are able to constrain (strong-field) parametrized post-Newtonian parameters $\hat{\alpha}_1$, $\hat{\alpha}_2$, $\hat{\xi}$ to high precision, among which, $|\hat{\xi}| < 3.1\times10ˆ{-4}$ (95% C.L.) is reported here for the first time.

#### Nov 30, 2012

1211.6558 (/preprints)
2012-11-30, 21:52 

## [1211.6884] A set of invariant quality factors measuring the deviation from the Kerr metric

Authors: Alfonso Garc&#xed;a-Parrado G&#xf3;mez-Lobo, Jos&#xe9; M. M. Senovilla

Date: 29 Nov 2012

Abstract: A number of scalar invariant characterizations of the Kerr solution are presented. These characterizations come in the form of quality factors defined in stationary space-times. A quality factor is a scalar quantity varying in the interval $[0,1]$ with the value 1 being attained if and only if the space-time is locally isometric to the Kerr solution. No knowledge of the Kerr solution is required to compute these quality factors. A number of different possibilities arise depending on whether the space-time is Ricci-flat and asymptotically flat, just Ricci-flat, or Ricci non-flat. In each situation a number of quality factors are constructed and analysed. The relevance of these quality factors is clear in any situation where one seeks a rigorous formulation of the statement that a space-time is "close" to the Kerr solution, such as: its non-linear stability problem, the asymptotic settlement of a radiating isolated system undergoing gravitational collapse, or in the formulation of some uniqueness results.

#### Nov 30, 2012

1211.6884 (/preprints)
2012-11-30, 21:51 

## [1211.6738] Sowing the seeds of massive black holes in small galaxies: Young clusters as the building blocks of Ultra-Compact-Dwarf Galaxies

Authors: Pau Amaro-Seoane, Symeon Konstantinidis, Marc Dewi Freitag, M. Coleman Miller, Frederic A. Rasio

Date: 28 Nov 2012

Abstract: Interacting galaxies often have complexes of hundreds of young stellar clusters of individual masses ~ 10ˆ{4-6} Msun in regions that are a few hundred parsecs across. These cluster complexes interact dynamically, and their coalescence is a candidate for the origin of some ultracompact dwarf galaxies (UCDs). Individual clusters with short relaxation times are candidates for the production of intermediate-mass black holes of a few hundred solar masses, via runaway stellar collisions prior to the first supernovae in a cluster. It is therefore possible that a cluster complex hosts multiple intermediate-mass black holes that may be ejected from their individual clusters due to mergers or binary processes, but bound to the complex as a whole. Here we explore the dynamical interaction between initially free-flying massive black holes and clusters in an evolving cluster complex. We find that, after hitting some clusters, it is plausible that the massive black hole will be captured in an ultracompact dwarf forming near the center of the complex. In the process, the hole typically triggers electromagnetic flares via stellar disruptions, and is also likely to be a prominent source of gravitational radiation for the advanced ground-based detectors LIGO and VIRGO. We also discuss other implications of this scenario, notably that the central black hole could be considerably larger than expected in other formation scenarios for ultracompact dwarfs.

#### Nov 30, 2012

1211.6738 (/preprints)
2012-11-30, 12:27 

## [1211.6184] Template banks to search for low-mass binary black holes in advanced gravitational-wave detectors

Authors: Duncan A. Brown, Prayush Kumar, Alexander H. Nitz

Date: 27 Nov 2012

Abstract: Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range 3 Msolar <= m1, m2 <= 25 Msolar. We also show that the (computationally less expensive) TaylorF2 post-Newtonian waveforms can be used in place of EOBNRv2 waveforms when M <~ 12 Msolar. Finally, we investigate the effect of modes other than the dominant {l = m = 2} mode in BBH searches. We find that for systems with m1/m2 <= 1.5, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes greater than {l = m = 2} in the template waveforms. For higher mass ratios, including higher order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter in Advanced LIGO and Advanced Virgo.

#### Nov 27, 2012

1211.6184 (/preprints)
2012-11-27, 18:53 

## [1211.5377] Gravitational waves and stalled satellites from massive galaxy mergers at z < 1

Authors: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

Date: 22 Nov 2012

Abstract: We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black-hole binary mergers in the low redshift universe (z < 1) implied by this model, and find that this population has a signal-to-noise ratio as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c(f =1 yrˆ{-1})=5.8 x 10ˆ{-15} that is already in tension with observational constraints, and a 2-sigma lower limit within this model of h_c(f =1 yrˆ{-1})=2.0 x 10ˆ{-15}. The strength of this signal may therefore be detectable with the data already collected using the current generation of pulsar timing arrays, and could be detected with high statistical significance under conservative assumptions within the next few years, if the principle assumption of merger-driven galaxy evolution since z=1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10ˆ{39} erg/s, which is consistent with the statistics of observed ULXs.

#### Nov 27, 2012

1211.5377 (/preprints)
2012-11-27, 18:53 

## [1211.5375] Systematic investigation of the expected gravitational wave signal from supermassive black hole binaries in the pulsar timing band

Authors: A. Sesana

Date: 22 Nov 2012

Abstract: In this letter we carry out the first systematic investigation of the expected gravitational wave (GW) background generated by supermassive black hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing arrays (PTAs). We take from the literature several estimates of the redshift dependent galaxy mass function and of the fraction of close galaxy pairs to derive a wide range of galaxy merger rates. We then exploit empirical black hole-host relations to populate merging galaxies with SMBHs. The result of our procedure is a collection of a large number of phenomenological SMBH binary merger rates consistent with current observational constraints on the galaxy assembly at z<1.5. For each merger rate we compute the associated GW signal, eventually producing a large set of estimates of the nHz GW background that we use to infer confidence intervals of its expected amplitude. When considering the most recent SMBH-host relations, accounting for ultra-massive black holes in brightest cluster galaxies, we find that the nominal $1\sigma$ interval of the expected GW signal is only a factor of 3-to-10 below current PTA limits, implying a non negligible chance of detection in the next few years.

#### Nov 27, 2012

1211.5375 (/preprints)
2012-11-27, 09:23 

## [1211.6095] Black hole mass dynamics and renormalization group evolution

Authors: Walter D. Goldberger, Andreas Ross, Ira Z. Rothstein

Date: 26 Nov 2012

Abstract: We examine the real-time dynamics of a system of one or more black holes interacting with long wavelength gravitational fields. We find that the (classical) renormalizability of the effective field theory that describes this system necessitates the introduction of a time dependent mass counterterm, and consequently the mass parameter must be promoted to a dynamical degree of freedom. To track the time evolution of this dynamical mass, we compute the expectation value of the energy-momentum tensor within the in-in formalism, and fix the time dependence by imposing energy-momentum conservation. Mass renormalization induces logarithmic ultraviolet divergences at quadratic order in the gravitational coupling, leading to a new time-dependent renormalization group (RG) equation for the mass parameter. We solve this RG equation and use the result to predict heretofore unknown high order logarithms in the energy distribution of gravitational radiation emitted from the system.

#### Nov 27, 2012

1211.6095 (/preprints)
2012-11-27, 09:22 

## [1211.5601] Blocking low-eccentricity EMRIs: A statistical direct-summation N-body study of the Schwarzschild barrier

Authors: Patrick Brem, Pau Amaro-Seoane, Carlos F. Sopuerta

Date: 23 Nov 2012

Abstract: The capture of a compact object in a galactic nucleus by a massive black hole (MBH), an extreme-mass ratio inspiral (EMRI), is the best way to map space and time around it. Recent work on stellar dynamics has demonstrated that there seems to be a complot in phase space acting on low-eccentricity captures, since their rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques, and thus it affects the enhancement on lower-eccentricity EMRIs that one would expect from resonant relaxation. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian and also for the first time in a direct-summation code a geodesic approximation for the relativistic orbits. The existence of the barrier prevents low-eccentricity EMRIs from approaching the central MBH, but high-eccentricity EMRIs, which have been wrongly classified as "direct plunges" until recently, ignore the presence of the barrier, because they are driven by two-body relaxation. Hence, since the rates are significantly affected in the case of low-eccentricity EMRIs, we predict that a LISA-like observatory such as eLISA will predominantly detect high-eccentricity EMRIs.

#### Nov 27, 2012

1211.5601 (/preprints)
2012-11-27, 09:22 

## [1211.4609] Is there an intermediate massive black hole in the Galactic center: Imprints on the stellar tidal-disruption rate

Authors: Xian Chen (KIAA-PKU), F. K. Liu (PKU)

Date: 19 Nov 2012

Abstract: It has been suggested that an intermediate-massive black hole (IMBH) with mass 10ˆ{3-5} M_\odot could fall into the galactic center (GC) and form an massive black hole binary (MBHB) with the central supermassive black hole, but current observational are not sensitive to constrain all mass and distance ranges. Motivated by the recent discovery that MBHBs could enhance the rate of tidal-disruption events (TDEs) of stellar objects, we investigate the prospect of using stellar-disruption rate to probe IMBHs in the GC. We incorporated the perturbation by an IMBH into the loss-cone theory and calculated the stellar-disruption rates in the GC. We found that an IMBH heavier than 2000 M_\odot could distinguishably enhance the stellar-disruption rate. By comparing observations of Sgr A* with the fall-back model for stellar debris, we suggested that the TDE rate in our Galaxy should not significantly exceed 0.002 per year, therefore a fraction of the parameter space for the IMBH, concentrating at the high-mass end, can already be excluded. To derive constraint in the remaining parameter space, it is crucial to observationally confirm or reject the stellar-disruption rate between 10ˆ{-4} and 0.01 yrˆ{-1}, and we discussed possible strategies to make such measurements.

#### Nov 26, 2012

1211.4609 (/preprints)
2012-11-26, 11:43 

## [1211.4590] The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays

Authors: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

Date: 19 Nov 2012

Abstract: Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.

#### Nov 26, 2012

1211.4590 (/preprints)
2012-11-26, 11:43 

## [1211.3816] Is a tabletop search for Planck scale signals feasible

Authors: Jacob D. Bekenstein

Date: 16 Nov 2012

Abstract: Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.

#### Nov 26, 2012

1211.3816 (/preprints)
2012-11-26, 11:43 

## [1211.4107] Free motion around black holes with discs or rings: between integrability and chaos - II

Authors: O. Semer&#xe1;k, P. Sukov&#xe1;

Date: 17 Nov 2012

Abstract: We continue the study of time-like geodesic dynamics in exact static, axially and reflection symmetric space-times describing the fields of a Schwarzschild black hole surrounded by thin discs or rings. In the previous paper, the rise (and decline) of geodesic chaos with ring/disc mass and position and with test particle energy was revealed on Poincaré sections, on time series of position or velocity and their power spectra, and on time evolution of the orbital ‘latitudinal action’. In agreement with the KAM theory of nearly integrable dynamical systems and with the results observed in similar gravitational systems in the literature, we found orbits of very different degrees of chaoticity in the phase space of perturbed fields. Here we compare selected orbits in more detail and try to classify them according to the characteristics of the corresponding phase-variable time series, mainly according to the shape of the time-series power spectra, and also applying two recurrence methods: the method of ‘average directional vectors’, which traces the directions in which the trajectory (recurrently) passes through a chosen phase-space cell, and the ‘recurrence-matrix’ method, which consists of statistics over the recurrences themselves. All the methods proved simple and powerful, while it is interesting to observe how they differ in sensitivity to certain types of behaviour.

#### Nov 26, 2012

1211.4107 (/preprints)
2012-11-26, 11:43 

## [1211.4106] Free motion around black holes with discs or rings: between integrability and chaos - I

Authors: O. Semer&#xe1;k, P. Sukov&#xe1;

Date: 17 Nov 2012

Abstract: Geodesic dynamics is regular in the fields of isolated stationary black holes. However, due to the presence of unstable periodic orbits, it easily becomes chaotic under various perturbations. Here we examine what amount of chaoticity is induced in Schwarzschild space-time by a presence of an additional source. Following astrophysical motivation, we specifically consider thin rings or discs lying symmetrically around the hole, and describe the total field in terms of exact static and axially symmetric solutions of Einstein's equations. The growth of chaos in time-like geodesic motion is illustrated on Poincaré sections, on time series of position or velocity and their Fourier spectra, and on time evolution of the orbital ‘latitudinal action’. The results are discussed in dependence on the mass and position of the ring/disc and on geodesic parameters (energy and angular momentum). In the Introduction, we also add an overview of the literature.

#### Nov 26, 2012

1211.4106 (/preprints)
2012-11-26, 11:43 

## [1211.5091] The influence of star formation history on the gravitational wave signal from close double degenerates in the thin disc

Authors: Shenghua Yu, C. Simon Jeffery

Date: 21 Nov 2012

Abstract: The expected gravitational wave (GW) signal due to double degenerates (DDs) in the thin Galactic disc is calculated using a Monte Carlo simulation. The number of young close DDs that will contribute observable discrete signals in the frequency range $1.58 - 15.8$ mHz is estimated by comparison with the sensitivity of proposed GW observatories. The present-day DD population is examined as a function of Galactic star-formation history alone. It is shown that the frequency distribution, in particular, is a sensitive function of the Galactic star formation history and could be used to measure the time since the last major star-formation epoch.

#### Nov 25, 2012

1211.5091 (/preprints)
2012-11-25, 21:53 

## [1211.4871] On the orientation and magnitude of the black hole spin in galactic nuclei

Authors: M. Dotti, M. Colpi, S. Pallini, A. Perego, M. Volonteri

Date: 20 Nov 2012

Abstract: Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.

#### Nov 25, 2012

1211.4871 (/preprints)
2012-11-25, 21:53 

## [1211.5535] Gravitational Waves from a Particle in Circular Orbits around a Schwarzschild Black Hole to the 22nd Post-Newtonian Order

Authors: Ryuichi Fujita

Date: 23 Nov 2012

Abstract: We extend our previous results of the 14th post-Newtonian (PN) order expansion of gravitational waves for a test particle in circular orbits around a Schwarzschild black hole to the 22PN order, i.e. $vˆ{44}$ beyond the leading Newtonian approximation where $v$ is the orbital velocity of a test particle. Comparing our 22PN formula for the energy flux with high precision numerical results, we find that the relative error of the 22PN flux at the innermost stable circular orbit is about $10ˆ{-5}$. We also estimate the phase difference between the 22PN waveforms and numerical waveforms after a two-year inspiral. We find that the dephase is about $10ˆ{-9}$ for $\mu/M=10ˆ{-4}$ and $10ˆ{-2}$ for $\mu/M=10ˆ{-5}$ where $\mu$ is the mass of the compact object and $M$ the mass of the central supermassive black hole. Finally, we construct a hybrid formula of the energy flux by supplementing the 4PN formula of the energy flux for circular and equatorial orbits around a Kerr black hole with all the present 22PN terms for the case of a Schwarzschild black hole. Comparing the hybrid formula with the the full numerical results, we examine the performance of the hybrid formula for the case of Kerr black hole.

#### Nov 25, 2012

1211.5535 (/preprints)
2012-11-25, 21:53 

## [1211.5410] First-Order Perturbative Hamiltonian Equations of Motion for a Point Particle Orbiting a Schwarzschild Black Hole

Authors: Huan Yang, Haixing Miao, Yanbei Chen

Date: 23 Nov 2012

Abstract: We formulate a spherical harmonically decomposed 1+1 scheme to self-consistently evolve the trajectory of a point particle and its gravitational metric perturbation to a Schwarzschild background spacetime. Following the work of Moncrief, we write down an action for perturbations in space-time geometry, combine that with the action for a point-particle, and then obtain Hamiltonian equations of motion for metric perturbations, the particle's coordinates, as well as their canonical momenta. Hamiltonian equations for the metric-perturbation and their conjugate momenta reduce to Zerilli-Moncrief and Regge-Wheeler master equations with source terms, which are gauge invariant, plus auxiliary equations that specify gauge. Hamiltonian equations for the particle, on the other hand, now include effect of metric perturbations - with these new terms derived from the same interaction Hamiltonian that had lead to those well-known source terms. In this way, space-time geometry and particle motion can be evolved in a self-consistent manner, in principle in any gauge. However, the point-particle nature of our source requires regularization, and we outline how the Detweiler-Whiting approach can be applied. In this approach, a singular field can be obtained using Hadamard decomposition of the Green's function and the regular field, which needs to be evolved numerically, is the result of subtracting the singular field from the total metric perturbation. In principle, any gauge that has the singular-regular field decomposition is suitable for our self-consistent scheme. In reality, however, this freedom is only possible if our singular field has a high enough level of smoothness. In the case of Lorenz gauge, for each l and m, we have 2 wave equations to evolve gauge invariant quantities and 8 first order differential equations to fix the gauge and determine the metric components.

#### Nov 25, 2012

1211.5410 (/preprints)
2012-11-25, 21:53 

## [1211.3258] Seeking for the leading actor on the cosmic stage: Galaxies versus Supermassive Black Holes

Authors: Angela Bongiorno, Francesco Shankar, Francesca Civano, Isabelle Gavignaud, Antonis Georgakakis

Date: 14 Nov 2012

Abstract: We present a Special Issue on the interplay of galaxies and Supermassive Black Holes (SMBHs) recently published in Advances in Astronomy. This is the introductory paper containing the motivation for this Special Issue together with a brief description of the articles which are part of the manuscript and the link to the entire book (this http URL). We hope this Special Issue will be useful for many astronomers who want to get an update on the current status of the AGN-Galaxy coevolution topic.

#### Nov 15, 2012

1211.3258 (/preprints)
2012-11-15, 23:05 

## [1211.3372] Retention of Stellar-Mass Black Holes in Globular Clusters

Authors: Meagan Morscher, Stefan Umbreit, Will M. Farr, Frederic A. Rasio

Date: 14 Nov 2012

Abstract: Globular clusters should be born with significant numbers of stellar-mass black holes (BHs). It has been thought for two decades that very few of these BHs could be retained through the cluster lifetime. With masses ~10 MSun, BHs are ~20 times more massive than an average cluster star. They segregate into the cluster core, where they may eventually decouple from the remainder of the cluster. The small-N core then evaporates on a short timescale. This is the so-called Spitzer instability. Here we present the results of a full dynamical simulation of a globular cluster containing many stellar-mass BHs with a realistic mass spectrum. Our Monte Carlo simulation code includes detailed treatments of all relevant stellar evolution and dynamical processes. Our main finding is that old globular clusters could still contain many BHs at present. In our simulation, we find no evidence for the Spitzer instability. Instead, most of the BHs remain well-mixed with the rest of the cluster, with only the innermost few tens of BHs segregating significantly. Over the 12 Gyr evolution, fewer than half of the BHs are dynamically ejected through strong binary interactions in the cluster core. The presence of BHs leads to long-term heating of the cluster, ultimately producing a core radius on the high end of the distribution for Milky Way globular clusters (and those of other galaxies). A crude extrapolation from our model suggests that the BH--BH merger rate from globular clusters could be comparable to the rate in the field.

#### Nov 15, 2012

1211.3372 (/preprints)
2012-11-15, 23:05 

## [1211.3651] Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes

Authors: Jonathan C. McKinney (1 and 2), Alexander Tchekhovskoy (3), Roger D. Blandford (1) ((1) Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, (2) University of Maryland at College Park, Dept. of Physics, Joint Space-Science Institute, (3) Center for Theoretical Science, Jadwin Hall, Princeton University, Princeton Center for Theoretical Science Fellow)

Date: 15 Nov 2012

Abstract: Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH's spin magnitude and direction. While thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various BH spin vectors and disk thicknesses with magnetic flux reaching saturation. Our simulations reveal a "magneto-spin alignment" mechanism that causes magnetized disks and jets to align with the BH spin near BHs and further away to reorient with the outer disk. This mechanism has implications for the evolution of BH mass and spin, BH feedback on host galaxies, and resolved BH images for SgrA* and M87.

#### Nov 15, 2012

1211.3651 (/preprints)
2012-11-15, 23:04 

## [1211.3138] Pulsars are cool. Seriously

Authors: Scott M. Ransom

Date: 13 Nov 2012

Abstract: Ever since the first pulsar was discovered by Bell and Hewish over 40 years ago, we've known that not only are pulsars fascinating and truly exotic objects, but that we can use them as powerful tools for basic physics and astrophysics as well. Taylor and Hulse hammered these views home with their discovery and timing of the spectacular "binary pulsar" in the 1970s and 1980s. In the last two decades a host of surprises and a promise of phenomenal scientific riches in the future has come from the millisecond pulsars. As our instrumentation has become more sensitive and better suited to measuring the pulses from these objects, they've given us new tests of general relativity, fantastic probes of the interstellar medium, constraints on the physics of ultra-dense matter, new windows into binary and stellar evolution, and the promise of a direct detection of gravitational waves. These things really are cool, and there is much more we will do with them in the future.

#### Nov 15, 2012

1211.3138 (/preprints)
2012-11-15, 22:48 

## [1211.2748] Spinning dust radiation: a review of the theory

Authors: Yacine Ali-Ha&#xef;moud

Date: 12 Nov 2012

Abstract: This article reviews the current status of theoretical modeling of electric dipole radiation from spinning dust grains. The fundamentally simple problem of dust grain rotation appeals to a rich set of concepts of classical and quantum physics, owing the the diversity of processes involved. Rotational excitation and damping rates through various mechanisms are discussed, as well as methods of computing the grain angular momentum distribution function. Assumptions on grain properties are reviewed. The robustness of theoretical predictions now seems mostly limited by the uncertainties regarding the grains themselves, namely their abundance, dipole moments, size and shape distribution.

#### Nov 13, 2012

1211.2748 (/preprints)
2012-11-13, 17:42 

## [1211.2457] Probing gravitation with pulsars

Authors: Michael Kramer (MPI fuer Radioastronomie, Bonn, Germany / Jodrell Bank Centre for Astrophysics, University of Manchester, UK)

Date: 11 Nov 2012

Abstract: Radio pulsars are fascinating and extremely useful objects. Despite our on-going difficulties in understanding the details of their emission physics, they can be used as precise cosmic clocks in a wide-range of experiments -- in particular for probing gravitational physics. While the reader should consult the contributions to these proceedings to learn more about this exciting field of discovering, exploiting and understanding pulsars, we will concentrate here on on the usage of pulsars as gravity labs.

#### Nov 13, 2012

1211.2457 (/preprints)
2012-11-13, 17:40 

## [1211.1060] First Law of Mechanics for Black Hole Binaries with Spins

Authors: Luc Blanchet, Alessandra Buonanno, Alexandre Le Tiec

Date: 5 Nov 2012

Abstract: We use the canonical Hamiltonian formalism to generalize to spinning point particles the first law of mechanics established for binary systems of non-spinning point masses moving on circular orbits [Le Tiec, Blanchet, and Whiting, Phys. Rev. D 85, 064039 (2012)]. We find that the redshift observable of each particle is related in a very simple manner to the canonical Hamiltonian and, more generally, to a class of Fokker-type Hamiltonians. Our results are valid through linear order in the spin of each particle, but hold also for quadratic couplings between the spins of different particles. The knowledge of spin effects in the Hamiltonian allows us to compute spin-orbit terms in the redshift variable through 2.5PN order, for circular orbits and spins aligned or anti-aligned with the orbital angular momentum. To describe extended bodies such as black holes, we supplement the first law for spinning point-particle binaries with some "constitutive relations" that can be used for diagnosis of spin measurements in quasi-equilibrium initial data.

#### Nov 08, 2012

1211.1060 (/preprints)
2012-11-08, 23:07 

## [1211.1254] Towards Rapid Parameter Estimation on Gravitational Waves from Compact Binaries using Interpolated Waveforms

Authors: R. J. E. Smith, K. Cannon, C. Hanna, D. Keppel, I. Mandel

Date: 6 Nov 2012

Abstract: Accurate parameter estimation of gravitational waves from coalescing compact binary sources is a key requirement for gravitational-wave astronomy. Evaluating the posterior probability density function of the binary's parameters (component masses, sky location, distance, etc.) requires computing millions of waveforms. The computational expense of parameter estimation is dominated by waveform generation and scales linearly with the waveform computational cost. Previous work showed that gravitational waveforms from non-spinning compact binary sources are amenable to a truncated singular value decomposition, which allows them to be reconstructed via interpolation at fixed computational cost. However, the accuracy requirement for parameter estimation is typically higher than for searches, so it is crucial to ascertain that interpolation does not lead to significant errors. Here we provide a proof of principle to show that interpolated waveforms can be used to recover posterior probability density functions with negligible loss in accuracy with respect to non-interpolated waveforms. This technique has the potential to significantly increase the efficiency of parameter estimation.

#### Nov 08, 2012

1211.1254 (/preprints)
2012-11-08, 23:07 

## [1211.1227] Gravitational waves signal analysis

Authors: Ll. Bel

Date: 5 Nov 2012

Abstract: I use a very simplified example to discuss the signature of a gravitational wave taking into account the relative state of motion of the detector with respect to the source that originated it. Something that to my knowledge has been ignored up to now and may ruin the best crafted template \cite{Templates}.

#### Nov 08, 2012

1211.1227 (/preprints)
2012-11-08, 23:07 

## [1211.1374] Testing General Relativity and gravitational physics using the LARES satellite

Authors: Ignazio Ciufolini, Antonio Paolozzi, Erricos Pavlis, John Ries, Vahe Gurzadyan, Rolf Koenig, Richard Matzner, Roger Penrose, Giampiero Sindoni

Date: 6 Nov 2012

Abstract: The discovery of the accelerating expansion of the Universe, thought to be driven by a mysterious form of ‘dark energy’ constituting most of the Universe, has further revived the interest in testing Einstein's theory of General Relativity. At the very foundation of Einstein's theory is the geodesic motion of a small, structureless test-particle. Depending on the physical context, a star, planet or satellite can behave very nearly like a test-particle, so geodesic motion is used to calculate the advance of the perihelion of a planet's orbit, the dynamics of a binary pulsar system and of an Earth orbiting satellite. Verifying geodesic motion is then a test of paramount importance to General Relativity and other theories of fundamental physics. On the basis of the first few months of observations of the recently launched satellite LARES, its orbit shows the best agreement of any satellite with the test-particle motion predicted by General Relativity. That is, after modelling its known non-gravitational perturbations, the LARES orbit shows the smallest deviations from geodesic motion of any artificial satellite. LARES-type satellites can thus be used for accurate measurements and for tests of gravitational and fundamental physics. Already with only a few months of observation, LARES provides smaller scatter in the determination of several low-degree geopotential coefficients (Earth gravitational deviations from sphericity) than available from observations of any other satellite or combination of satellites.

#### Nov 08, 2012

1211.1374 (/preprints)
2012-11-08, 23:06 

## [1211.1385] Binary Millisecond Pulsar Discovery via Gamma-Ray Pulsations

Authors: H. J. Pletsch, L. Guillemot, H. Fehrmann, B. Allen, M. Kramer, C. Aulbert, M. Ackermann, M. Ajello, A. de Angelis, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, A. W. Borgland, E. Bottacini, T. J. Brandt, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, &#xd6;. Celik, E. Charles, R.C.G. Chaves, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Cutini, F. D&#x27;Ammando, C. D. Dermer, S. W. Digel, P. S. Drell, A. Drlica-Wagner, R. Dubois, D. Dumora, C. Favuzzi, E. C. Ferrara, A. Franckowiak, Y. Fukazawa, P. Fusco, F. Gargano, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, G. Godfrey, I. A. Grenier, M.-H. Grondin, J. E. Grove, S. Guiriec, D. Hadasch, Y. Hanabata, A. K. Harding, P. R. den Hartog, M. Hayashida, E. Hays, A. B. Hill, X. Hou, R. E. Hughes, G. Johannesson, M. S. Jackson, T. Jogler, A. S. Johnson, W. N. Johnson, J. Kataoka, M. Kerr, J. Kn&#xf6;dlseder, M. Kuss, J. Lande, S. Larsson, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, M. N. Lovellette, P. Lubrano, F. Massaro, M. Mayer, M. N. Mazziotta, J. E. McEnery, J. Mehault, P. F. Michelson, W. Mitthumsiri, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, T. Nakamori, R. Nemmen, E. Nuss, M. Ohno, T. Ohsugi, N. Omodei, M. Orienti, E. Orlando, F. de Palma, D. Paneque, J. S. Perkins, F. Piron, G. Pivato, T. A. Porter, S. Raino, R. Rando, P. S. Ray, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, R. W. Romani, C. Romoli, D. A. Sanchez, P. M. Saz Parkinson, A. Schulz, C. Sgro, E. do Couto e Silva, E. J. Siskind, D. A. Smith, G. Spandre, P. Spinelli, D. J. Suson, H. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo, M. Tinivella, E. Troja, T. L. Usher, J. Vandenbroucke, V. Vasileiou, G. Vianello, V. Vitale, A. P. Waite, B. L. Winer, K. S. Wood, M. Wood, Z. Yang, S. Zimmer

Date: 6 Nov 2012

Abstract: Millisecond pulsars (MSPs), old neutron stars spun-up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.

#### Nov 08, 2012

1211.1385 (/preprints)
2012-11-08, 23:05 

## [1210.7238] Comparing H-alpha and HI Surveys as Means to a Complete Local Galaxy Catalog in the Advanced LIGO/Virgo Era

Authors: Brian D. Metzger, David L. Kaplan, Edo Berger

Date: 26 Oct 2012

Abstract: Identifying the electromagnetic counterparts of gravitational wave (GW) sources detected by upcoming networks of advanced ground-based interferometers will be challenging due in part to the large number of unrelated astrophysical transients within the ~10-100 square degree sky localizations. A potential way to greatly reduce the number of such false positives is to limit detailed follow-up to only those candidates near galaxies within the GW sensitivity range of ~200 Mpc for binary neutron star mergers. Such a strategy is currently hindered by the fact that galaxy catalogs are grossly incomplete within this volume. Here we compare two methods for completing the local galaxy catalog: (1) a narrow-band H-alpha imaging survey; and (2) an HI emission line radio survey. Using H-alpha fluxes, stellar masses (M_star), and star formation rates (SFR) from galaxies in the Sloan Digital Sky Survey (SDSS), combined with HI data from the GALEX Arecibo SDSS Survey and the Herschel Reference Survey, we estimate that a H-alpha survey with a luminosity sensitivity of L_H-alpha = 1e40 erg/s at 200 Mpc could achieve a completeness of f_SFR ~ 75% with respect to total SFR, but only f_Mstar ~ 33% with respect to stellar mass (due to lack of sensitivity to early-type galaxies). These numbers are significantly lower than those achieved by an idealized spectroscopic survey due to the loss of H-alpha flux resulting from resolving out nearby galaxies and the inability to correct for the underlying stellar continuum. An HI survey with sensitivity similar to the proposed WALLABY survey on ASKAP could achieve f_SFR ~ 80% and f_Mstar ~ 50%, somewhat higher than that of the H-alpha survey. Finally, both H-alpha and HI surveys should achieve > 50% completeness with respect to the host galaxies of short duration gamma-ray bursts, which may trace the population of binary neutron star mergers.

#### Nov 06, 2012

1210.7238 (/preprints)
2012-11-06, 11:53 

## [1211.0546] Degeneracy between mass and spin in black-hole-binary waveforms

Authors: Emily Baird, Stephen Fairhurst, Mark Hannam, Patricia Murphy

Date: 2 Nov 2012

Abstract: We explore the degeneracy between mass and spin in gravitational waveforms emitted by black-hole binary coalescences. We focus on spin-aligned waveforms and obtain our results using phenomenological models that were tuned to numerical-relativity simulations. A degeneracy is known for low-mass binaries (particularly neutron-star binaries), where gravitational-wave detectors are sensitive to only the inspiral phase, and the waveform can be modelled by post-Newtonian theory. Here, we consider black-hole binaries, where detectors will also be sensitive to the merger and ringdown, and demonstrate that the degeneracy persists across a broad mass range. At low masses, the degeneracy is between mass ratio and total spin, with chirp mass accurately determined. At higher masses, the degeneracy persists but is not so clearly characterised by constant chirp mass as the merger and ringdown become more significant. We consider the importance of this degeneracy both for performing searches (including searches where only non-spinning templates are used) and in parameter extraction from observed systems. We compare observational capabilities between the early (~2015) and final (2018 onwards) versions of the Advanced LIGO detector.

#### Nov 06, 2012

1211.0546 (/preprints)
2012-11-06, 11:53 

## [1210.7969] Metric perturbations from eccentric orbits on a Schwarzschild black hole: I. Odd-parity Regge-Wheeler to Lorenz gauge transformation and two new methods to circumvent the Gibbs phenomenon

Authors: Seth Hopper, Charles R. Evans

Date: 30 Oct 2012

Abstract: We calculate the odd-parity, radiative ($\ell \ge 2$) parts of the metric perturbation in Lorenz gauge caused by a small compact object in eccentric orbit about a Schwarzschild black hole. The Lorenz gauge solution is found via gauge transformation from a corresponding one in Regge-Wheeler gauge. Like the Regge-Wheeler gauge solution itself, the gauge generator is computed in the frequency domain and transferred to the time domain. The wave equation for the gauge generator has a source with a compact, moving delta-function term and a discontinuous non-compact term. The former term allows the method of extended homogeneous solutions to be applied (which circumvents the Gibbs phenomenon). The latter has required the development of new means to use frequency domain methods and yet be able to transfer to the time domain while avoiding Gibbs problems. Two new methods are developed to achieve this: a partial annihilator method and a method of extended particular solutions. We detail these methods and show their application in calculating the odd-parity gauge generator and Lorenz gauge metric perturbations. A subsequent paper will apply these methods to the harder task of computing the even-parity parts of the gauge generator.

#### Nov 05, 2012

1210.7969 (/preprints)
2012-11-05, 08:51 

## [1210.8066] Observing extreme-mass-ratio inspirals with eLISA/NGO

Authors: Jonathan R Gair, Edward K Porter

Date: 30 Oct 2012

Abstract: The extreme-mass-ratio inspirals (EMRIs) of stellar mass compact objects into massive black holes in the centres of galaxies are an important source of low-frequency gravitational waves for space-based detectors. We discuss the prospects for detecting these sources with the evolved Laser Interferometer Space Antenna (eLISA), recently proposed as an ESA mission candidate under the name NGO. We show that NGO could observe a few tens of EMRIs over its two year mission lifetime at redshifts z < 0.5 and describe how the event rate changes under possible alternative specifications of the eLISA design.

#### Nov 05, 2012

1210.8066 (/preprints)
2012-11-05, 08:51 

## [1210.8152] Compact Binary Progenitors of Short Gamma-Ray Bursts

Authors: Bruno Giacomazzo, Rosalba Perna, Luciano Rezzolla, Eleonora Troja, Davide Lazzati

Date: 30 Oct 2012

Abstract: In recent years, detailed observations and accurate numerical simulations have provided support to the idea that mergers of compact binaries containing either two neutron stars (NSs) or an NS and a black hole (BH) may constitute the central engine of short gamma-ray bursts (SGRBs). The merger of such compact binaries is expected to lead to the production of a spinning BH surrounded by an accreting torus. Several mechanisms can extract energy from this system and power the SGRBs. Here we make the novel connection between observations and numerical simulations of compact binary mergers, and use the current sample of SGRBs with measured energies to constrain the mass of their powering tori. By comparing the masses of the tori with the results of fully general-relativistic simulations, we are able, for the first time, to infer the properties of the binary progenitors which yield SGRBs. We find that most of the tori have masses smaller than 0.01 M_{sun}, favoring "high-mass" binary NSs mergers, i.e. binaries with total masses >~1.5 the maximum mass of an isolated NS. This has important consequences for the GW signals that may be detected in association with SGRBs, since "high-mass" systems do not form a long-lived hypermassive NS (HMNS) after the merger. While NS-BH systems cannot be excluded to be the engine of at least some of the SGRBs, the BH would need to have an initial spin of ~0.9, or higher.

#### Nov 05, 2012

1210.8152 (/preprints)
2012-11-05, 08:50 

## [1210.7857] Corner-cube retro-reflector instrument for advanced lunar laser ranging

Authors: Slava G. Turyshev, James G. Williams, William M. Folkner, Gary M. Gutt, Richard T. Baran, Randall C. Hein, Ruwan P. Somawardhana, John A. Lipa, Suwen Wang

Date: 29 Oct 2012

Abstract: Lunar laser ranging (LLR) has made major contributions to our understanding of the Moon's internal structure and the dynamics of the Earth-Moon system. Because of the recent improvements of the ground-based laser ranging facilities, the present LLR measurement accuracy is limited by the retro-reflectors currently on the lunar surface, which are arrays of small corner-cubes. Because of lunar librations, the surfaces of these arrays do not, in general, point directly at the Earth. This effect results in a spread of arrival times, because each cube that comprises the retroreflector is at a slightly different distance from the Earth, leading to the reduced ranging accuracy. Thus, a single, wide aperture corner-cube could have a clear advantage. In addition, after nearly four decades of successful operations the retro-reflectors arrays currently on the Moon started to show performance degradation; as a result, they yield still useful, but much weaker return signals. Thus, fresh and bright instruments on the lunar surface are needed to continue precision LLR measurements. We have developed a new retro-reflector design to enable advanced LLR operations. It is based on a single, hollow corner cube with a large aperture for which preliminary thermal, mechanical, and optical design and analysis have been performed. The new instrument will be able to reach an Earth-Moon range precision of 1-mm in a single pulse while being subjected to significant thermal variations present on the lunar surface, and will have low mass to allow robotic deployment. Here we report on our design results and instrument development effort.

#### Nov 05, 2012

1210.7857 (/preprints)
2012-11-05, 08:50 

## [1211.0038] Black hole solutions of modified gravity theories

Authors: Yannis Bardoux

Date: 31 Oct 2012

Abstract: The main interest of the work exposed in this thesis is to explore hairy black holes in a more general framework than General Relativity by taking into account the presence of a cosmological constant, of higher dimensions, of exotic matter fields or of higher curvature terms. These extensions to General Relativity can be derived in the context of String Theory. It is also by studying natural extensions to General Relativity that we can more deeply understand the theory of Einstein. Firstly, we will display the theory of General Relativity with its building blocks in particular and we will give the mathematical tools that we need afterwards. Then, a first extension will be detailed with the introduction of higher dimensions and p-form fields which constitute the natural generalization of the electromagnetic interaction. We will build in this framework new static black hole solutions where p-form fields allow to shape the geometry of the horizon. Secondly, we will present the general extension of Einstein theory in any dimension which produces second order field equations: Lovelock theory. We will determine in this context a large class of solutions in dimension 6 for which the theory is reduced to Einstein-Gauss-Bonnet theory with the presence of p-form fields. Thirdly, we will study a generalization of General Relativity in dimension 4 whose modification is induced by a conformally coupled scalar field. We will namely exhibit a new black hole solution with a flat horizon in the presence of axionic fields. To conclude this thesis, thermodynamical aspects of these gravitational theories will be studied. In this way, we will be able to determine the mass and the charges of these new solutions and we will examine phase transition phenomena in the presence of a conformally scalar field.

#### Nov 05, 2012

1211.0038 (/preprints)
2012-11-05, 08:48 

## [1211.0013] Scaling Relations Between Low-mass Black Holes and Their Host Galaxies

Authors: Qirong Zhu, Yuexing Li, Sydney Sherman

Date: 31 Oct 2012

Abstract: It is well established that supermassive black holes in nearby elliptical galaxies correlate tightly with the kinematic property ($\mbhsigma$ correlation) and stellar mass ($\mbhhost$ correlation) of their host spheroids. However, it is not clear what the relations would be at the low-mass end, and how they evolve. Here, we investigate these relations in low-mass systems ($\MBH \sim \rm{10ˆ{6}- 10ˆ{8}}\, \Msun$) using the Aquila Simulation, a high-resolution cosmological hydrodynamic simulation which follows the formation and evolution of stars and black holes in a Milky Way-size galaxy and its substructures. We find a number of interesting results on the origin and evolution of the scaling relations in these systems: (1) there is a strong redshift evolution in the $\mbhsigma$ relation, but a much weaker one in the $\mbhhost$ relation; (2) there is a close link between the $\mbhsigma$ relation and the dynamical state of the system -- the galaxies that fall on the observed correlation appear to have reached virial equilibrium. (3) the star formation and black hole growth are self-regulated in galaxies -- the ratio between black hole accretion rate and star formation rate remains nearly constant in a wide redshift span $z = 0-6$. These findings suggest that the observed correlations have different origins: the $\mbhsigma$ relation may be the result of virial equilibrium, while the $\mbhhost$ relation may the result of self-regulated star formation and black hole growth in galaxies.

#### Nov 05, 2012

1211.0013 (/preprints)
2012-11-05, 08:47 

## [1211.0021] Searches for continuous gravitational waves with the LIGO and Virgo detector

Authors: Keith Riles for the LIGO Scientific Collaboration, Virgo Collaboration

Date: 31 Oct 2012

Abstract: The LIGO Scientific Collaboration and Virgo Collaboration have carried out joint searches in LIGO and Virgo data for periodic continuous gravitational waves. These analyses range from targeted searches for gravitational-wave signals from known pulsars, for which precise ephemerides from radio or X-ray observations are used in matched filters, to all-sky searches for unknown neutron stars, including stars in binary systems. Between these extremes lie directed searches for known stars of unknown spin frequency or for new unknown sources at specific locations, such as near the galactic center or in globular clusters. Recent and ongoing searches of each type will be summarized, along with prospects for future searches using data from the Advanced LIGO and Virgo detectors.

#### Nov 05, 2012

1211.0021 (/preprints)
2012-11-05, 08:47