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Gravitational wave observations of eccentric binary black hole mergers will provide unequivocal evidence for the formation of these systems through dynamical assembly in dense stellar environments. The study of these astrophysically motivated sources is timely in view of electromagnetic observations, consistent with the existence of stellar mass black holes in the globular cluster M22 and in the galactic center, and the proven detection capabilities of ground-based gravitational wave detectors. In order to get insights into the physics of these objects in the dynamical, strong-field gravity regime, we present a catalog of 89 numerical relativity waveforms that describe binary systems of nonspinning black holes with mass ratios 1≤q≤10, and initial eccentricities as high as e0=0.18 fifteen cycles before merger. We use this catalog to quantify the loss of energy and angular momentum through gravitational radiation, and the astrophysical properties of the black hole remnant, including its final mass and spin, and recoil velocity. We discuss the implications of these results for gravitational wave source modeling, and the design of algorithms to search for and identify eccentric binary black hole mergers in realistic detection scenarios. [ABSTRACT FROM AUTHOR]

We present a code to construct initial data for binary neutron star systems in which the stars are rotating. Our code, based on a formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We compute the neutron star angular momentum through quasilocal angular momentum integrals. When constructing irrotational binary neutron stars, we find a very small residual dimensionless spin of ~2 x 10-4. Evolutions of rotating neutron star binaries show that the magnitude of the stars' angular momentum is conserved, and that the spin and orbit precession of the stars is well described by post-Newtonian approximation. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to ~0.1%. The neutron stars show quasinormal mode oscillations at an amplitude which increases with the rotation rate of the stars. [ABSTRACT FROM AUTHOR]

We present a first simulation of the post-merger evolution of a black hole-neutron star binary in full general relativity using an energy-integrated general-relativistic truncated moment formalism for neutrino transport. We describe our implementation of the moment formalism and important tests of our code, before studying the formation phase of an accretion disk after a black hole-neutron star merger. We use as initial data an existing general-relativistic simulation of the merger of a neutron star of mass 1.4M⊙ with a black hole of mass 7 M⊙ and dimensionless spin χBH = 0.8. Comparing with a simpler leakage scheme for the treatment of the neutrinos, we find noticeable differences in the neutron-to-proton ratio in and around the disk, and in the neutrino luminosity. We find that the electron neutrino luminosity is much lower in the transport simulations, and that both the disk and the disk outflows are less neutron rich. The spatial distribution of the neutrinos is significantly affected by relativistic effects, due to large velocities and curvature in the regions of strongest emission. Over the short time scale evolved, we do not observe purely neutrino-driven outflows. However, a small amount of material (3 × 10-4M⊙) is ejected in the polar region during the circularization of the disk. Most of that material is ejected early in the formation of the disk, and is fairly neutron rich (electron fraction Ye ~ 0.15-0.25). Through r-process nucleosynthesis, that material should produce high-opacity lanthanides in the polar region, and could thus affect the light curve of radioactively powered electromagnetic transients. We also show that by the end of the simulation, while the bulk of the disk remains neutron rich (Ye ~ 0.15-0.2 and decreasing), its outer layers have a higher electron fraction: 10% of the remaining mass has Ye > 0.3. As that material would be the first to be unbound by disk outflows on longer time scales, and as composition evolution is slower at later times, the changes in Ye experienced during the formation phase of the disk could have an impact on nucleosynthesis outputs from neutrino-driven and viscously driven outflows. Finally, we find that the effective viscosity due to momentum transport by neutrinos is unlikely to have a strong effect on the growth of the magnetorotational instability in the post-merger accretion disk. [ABSTRACT FROM AUTHOR]

We present a first exploration of the results of neutron star-black hole mergers using black hole masses in the most likely range of 1MQ-10MQ, a neutrino leakage scheme, and a modeling of the neutron star material through a finite-temperature nuclear-theory based equation of state. In the range of black hole spins in which the neutron star is tidally disrupted (ym{ > 0.7), we show that the merger consistently produces large amounts of cool (T < 1 MeV), unbound, neutron-rich material (Mej ~ 0.05Me -0.20Mo ). A comparable amount of bound matter is initially divided between a hot disk (Tmm ~ 15 MeV) with typical neutrino luminosity of Lv ~ 1053 erg/s, and a cooler tidal tail. After a short period of rapid protonization of the disk lasting ~10 ms, the accretion disk cools down under the combined effects of the fall-back of cool material from the tail, continued accretion of the hottest material onto the black hole, and neutrino emission. As the temperature decreases, the disk progressively becomes more neutron rich, with dimmer neutrino emission. This cooling process should stop once the viscous heating in the disk (not included in our simulations) balances the cooling. These mergers of neutron star-black hole binaries with black hole masses of MBH ~ 1MG-\()MQ, and black hole spins high enough for the neutron star to disrupt provide promising candidates for the production of short gamma-ray bursts, of bright infrared postmerger signals due to the radioactive decay of unbound material, and of large amounts of r-process nuclei. [ABSTRACT FROM AUTHOR]

We revisit the problem of computing the self-force on a scalar charge moving along an eccentric geodesic orbit around a Schwarzschild black hole. This work extends previous scalar self-force calculations for circular orbits, which were based on a regular "effective" point-particle source and a full 3D evolution code. We find good agreement between our results and previous calculations based on a (1 + 1) time-domain code. Finally, our data visualization is unconventional: we plot the self-force through full radial cycles to create "self-force loops," which reveal many interesting features that are less apparent in standard presentations of eccentric-orbit self-force data. [ABSTRACT FROM AUTHOR]

We examine Hubeny's scenario according to which a near-extremal Reissner-Nordstrom black hole can absorb a charged particle and be driven toward an over-extremal state in which the charge exceeds the mass, signaling the destruction of the black hole. Our analysis incorporates the particle's electromagnetic self-force and the energy radiated to infinity in the form of electromagnetic waves. With these essential ingredients, our sampling of the parameter space reveals no instances of an overcharged final state, and we conjecture that the self-force acts as a cosmic censor, preventing the destruction of a near-extremal black hole by the absorption of a charged particle. We argue, on the basis of the third law of black hole mechanics, that this conclusion is robust and should apply to attempts to overspin a Kerr black hole. [ABSTRACT FROM AUTHOR]

The last ten years have witnessed fast spreading of massively parallel computing clusters, from leading supercomputing facilities down to the average university computing center. Many companies in the private sector have undergone a similar evolution. In this scenario, the seamless integration of software and middleware libraries is a key ingredient to ensure portability of scientific codes and guarantees them an extended lifetime. In this work, we describe the integration of the ChASE library, a modern parallel eigensolver, into an existing legacy code for the first-principles computation of optical properties of materials via solution of the Bethe-Salpeter equation for the optical polarization function. Our numerical tests show that, as a result of integrating ChASE and parallelizing the reading routine, the code experiences a remarkable speedup and greatly improved scaling behavior on both multi- and many-core architectures. We demonstrate that such a modernized BSE code will, by fully exploiting parallel computing architectures and file systems, enable domain scientists to accurately study complex material systems that were not accessible before. [ABSTRACT FROM AUTHOR]

We introduce an improved version of the eccentric, nonspinning, inspiral-Gaussian-process merger approximant (ENIGMA) waveform model that utilizes a more stable and robust numerical method to smoothly connect the analytical relativity-based inspiral evolution with the numerical relativity-based merger phase. We find that this ready-to-use model can: (i) produce physically consistent signals, without reporting any failures, when sampling over 1M samples that were randomly chosen over the m {1, 2} ∈ [5 M ⊙, 50 M ⊙] parameter space, and the entire range of binary inclination angles; (ii) produce waveforms within 0.04 seconds, averaged over 1000 iterations, from an initial gravitational wave frequency f GW = 15     Hz and at a sample rate of 8192 Hz; and (iii) reproduce the physics of quasicircular mergers, since its overlap with SEOBNRv4 waveforms is O ≥ 0.99 assuming advanced LIGO zero detuned high power noise configuration, and signals generated from f GW = 15     Hz. We utilize ENIGMA to compute the expected signal-to-noise ratio (SNR) distributions of eccentric binary black hole mergers assuming the existence of second and third generation gravitational wave detector networks. For second generation detectors, we assume the geographical location and detection sensitivities of the twin LIGO detectors, Virgo, KAGRA, LIGO-India, and a LIGO-type detector in Australia. For third generation detectors, we assume the geographical location of second generation detectors, and use the proposed sensitivities of the Cosmic Explorer and the Einstein Telescope. In the context of advanced LIGO-type detectors, we find that the SNR of eccentric mergers is always larger than quasicircular mergers for systems with e 0 ≤ 0.4 at f GW = 10     Hz, even if the timespan of eccentric signals is just a third of quasicircular systems with identical total mass and mass-ratio. For Cosmic Explorer-type detector networks, we find that eccentric mergers have similar SNRs than quasicircular systems for e 0 ≤ 0.3 at f GW = 10     Hz. Systems with e 0 ∼ 0.5 at f GW = 10     Hz have SNRs that range between 50%-90% of the SNR produced by quasicircular mergers, even if these eccentric signals are just between a third to a tenth the length of quasicircular systems. For Einstein Telescope-type detectors, we find that eccentric mergers have similar SNRs than quasicircular systems for e 0 ≤ 0.4 at f GW = 5     Hz. The most eccentric events in our sample, e 0 ∼ 0.6 at f GW = 5     Hz, merge at least five times faster than quasicircular systems, and may be detectable with SNRs between 50%-85% the SNR of quasicircular mergers with identical binary components. [ABSTRACT FROM AUTHOR]

As gravitational-wave detectors become more sensitive and broaden their frequency bandwidth, we will access a greater variety of signals emitted by compact binary systems, shedding light on their astrophysical origin and environment. A key physical effect that can distinguish among different formation scenarios is the misalignment of the spins with the orbital angular momentum, causing the spins and the binary's orbital plane to precess. To accurately model such precessing signals, especially when masses and spins vary in the wide astrophysical range, it is crucial to include multipoles beyond the dominant quadrupole. Here, we develop the first multipolar precessing waveform model in the effective-one-body (EOB) formalism for the entire coalescence stage (i.e., inspiral, merger and ringdown) of binary black holes: SEOBNRv4PHM. In the nonprecessing limit, the model reduces to SEOBNRv4HM, which was calibrated to numerical-relativity (NR) simulations, and waveforms from black-hole perturbation theory. We validate SEOBNRv4PHM by comparing it to the public catalog of 1405 precessing NR waveforms of the Simulating eXtreme Spacetimes (SXS) collaboration, and also to 118 SXS precessing NR waveforms, produced as part of this project, which span mass ratios 1-4 and (dimensionless) black-hole's spins up to 0.9. We stress that SEOBNRv4PHM is not calibrated to NR simulations in the precessing sector. We compute the unfaithfulness against the 1523 SXS precessing NR waveforms, and find that, for 94% (57%) of the cases, the maximum value, in the total mass range 20-200 M⊙, is below 3% (1%). Those numbers change to 83% (20%) when using the inspiral-merger-ringdown, multipolar, precessing phenomenological model IMRPhenomPv3HM. We investigate the impact of such unfaithfulness values with two Bayesian, parameter-estimation studies on synthetic signals. We also compute the unfaithfulness between those waveform models as a function of the mass and spin parameters to identify in which part of the parameter space they differ the most. We validate them also against the multipolar, precessing NR surrogate model NRSur7dq4, and find that the SEOBNRv4PHM model outperforms IMRPhenomPv3HM. [ABSTRACT FROM AUTHOR]

We present 12 new simulations of unequal mass neutron star mergers. The simulations are performed with the spec code, and utilize nuclear-theory-based equations of state and a two-moment gray neutrino transport scheme with an improved energy estimate based on evolving the number density. We model the neutron stars with the SFHo, LS220, and DD2 equations of state (EOS) and we study the neutrino and matter emission of all 12 models to search for robust trends between binary parameters and emission characteristics. We find that the total mass of the dynamical ejecta exceeds 0.01 M⊙ only for SFHo with weak dependence on the mass ratio across all models. We find that the ejecta have a broad electron fraction (Ye) distribution (≈0.06-0.48), with mean 0.2. Ye increases with neutrino irradiation over time, but decreases with increasing binary asymmetry. We also find that the models have ejecta with a broad asymptotic velocity distribution (≈0.05-0.7c). The average velocity lies in the range 0.2c-0.3c and decreases with binary asymmetry. Furthermore, we find that disk mass increases with binary asymmetry and stiffness of the EOS. The Ye of the disk increases with softness of the EOS. The strongest neutrino emission occurs for the models with soft EOS. For (anti) electron neutrinos we find no significant dependence of the magnitude or angular distribution or neutrino luminosity with mass ratio. The heavier neutrino species have a luminosity dependence on mass ratio but an angular distribution which does not change with mass ratio. [ABSTRACT FROM AUTHOR]

We determine the mass ratio, eccentricity and binary inclination angles that maximize the contribution of the higher-order waveform multipoles (ℓ,|m|)={(2,2),(2,1),(3,3),(3,2),(3,1),(4,4),(4,3),(4,2),(4,1)} for the gravitational wave detection of eccentric binary black hole mergers. We carry out this study using numerical relativity waveforms that describe nonspinning black hole binaries with mass ratios 1≤q≤10, and orbital eccentricities as high as e0=0.18 fifteen cycles before merger. For stellar-mass, asymmetric mass-ratio, binary black hole mergers, and assuming LIGO's zero detuned high power configuration, we find that in regions of parameter space where black hole mergers modeled with ℓ=|m|=2 waveforms have vanishing signal-to-noise ratios, the inclusion of (ℓ,|m|) modes enables the observation of these sources with signal-to-noise ratios that range between 30% and 45% of the signal-to-noise ratio of optimally oriented binary black hole mergers modeled with ℓ=|m|=2 numerical relativity waveforms. Having determined the parameter space where (ℓ,|m|) modes are important for gravitational wave detection, we construct waveform signals that describe these astrophysically motivated scenarios and demonstrate that these topologically complex signals can be detected and characterized in real LIGO noise with deep learning algorithms. [ABSTRACT FROM AUTHOR]

Black hole-torus systems from compact binary mergers are possible engines for gamma-ray bursts (GRBs). During the early evolution of the postmerger remnant, the state of the torus is determined by a combination of neutrino cooling and magnetically driven heating processes, so realistic models must include both effects. In this paper, we study the postmerger evolution of a magnetized black hole-neutron star binary system using the Spectral Einstein Code (SpEC) from an initial postmerger state provided by previous numerical relativity simulations. We use a finite-temperature nuclear equation of state and incorporate neutrino effects in a leakage approximation. To achieve the needed accuracy, we introduce improvements to SpEC's implementation of general-relativistic magnetohydrodynamics (MHD), including the use of cubed-sphere multipatch grids and an improved method for dealing with supersonic accretion flows where primitive variable recovery is difficult. We find that a seed magnetic field triggers a sustained source of heating, but its thermal effects are largely cancelled by the accretion and spreading of the torus from MHD-related angular momentum transport. The neutrino luminosity peaks at the start of the simulation, and then drops significantly over the first 20 ms but in roughly the same way for magnetized and nonmagnetized disks. The heating rate and disk's luminosity decrease much more slowly thereafter. These features of the evolution are insensitive to grid structure and resolution, formulation of the MHD equations, and seed field strength, although turbulent effects are not fully converged. [ABSTRACT FROM AUTHOR]

We present ENIGMA, a time domain, inspiral-merger-ringdown waveform model that describes nonspinning binary black holes systems that evolve on moderately eccentric orbits. The inspiral evolution is described using a consistent combination of post-Newtonian theory, self-force and black hole perturbation theory. Assuming eccentric binaries that circularize prior to coalescence, we smoothly match the eccentric inspiral with a stand-alone, quasicircular merger, which is constructed using machine learning algorithms that are trained with quasicircular numerical relativity waveforms. We show that ENIGMA reproduces with excellent accuracy the dynamics of quasicircular compact binaries. We validate ENIGMA using a set of Einstein Toolkit eccentric numerical relativity waveforms, which describe eccentric binary black hole mergers with mass-ratios between 1≤q≤5.5, and eccentricities e0≲0.2 ten orbits before merger. We use this model to explore in detail the physics that can be extracted with moderately eccentric, nonspinning binary black hole mergers. In particular, we use ENIGMA to show that the gravitational wave transients GW150914, GW151226, GW170104, GW170814 and GW170608 can be effectively recovered with spinning, quasicircular templates if the eccentricity of these events at a gravitational wave frequency of 10 Hz satisfies e0≤{0.175,0.125,0.175,0.175,0.125}, respectively. We show that if these systems have eccentricities e0∼0.1 at a gravitational wave frequency of 10 Hz, they can be misclassified as quasicircular binaries due to parameter space degeneracies between eccentricity and spin corrections. Using our catalog of eccentric numerical relativity simulations, we discuss the importance of including higher-order waveform multipoles in gravitational wave searches of eccentric binary black hole mergers. [ABSTRACT FROM AUTHOR]

We present a time domain waveform model that describes the inspiral, merger and ringdown of compact binary systems whose components are nonspinning, and which evolve on orbits with low to moderate eccentricity. The inspiral evolution is described using third-order post-Newtonian equations both for the equations of motion of the binary, and its far-zone radiation field. This latter component also includes instantaneous, tails and tails-of-tails contributions, and a contribution due to nonlinear memory. This framework reduces to the post-Newtonian approximant TaylorT4 at third post-Newtonian order in the zero-eccentricity limit. To improve phase accuracy, we also incorporate higher-order post-Newtonian corrections for the energy flux of quasicircular binaries and gravitational self-force corrections to the binding energy of compact binaries. This enhanced prescription for the inspiral evolution is combined with a fully analytical prescription for the merger-ringdown evolution constructed using a catalog of numerical relativity simulations. We show that this inspiral-merger-ringdown waveform model reproduces the effective-one-body model of Ref. [Y. Pan et al., Phys. Rev. D 89, 061501 (2014).] for quasicircular black hole binaries with mass ratios between 1 to 15 in the zero-eccentricity limit over a wide range of the parameter space under consideration. Using a set of eccentric numerical relativity simulations, not used during calibration, we show that our new eccentric model reproduces the true features of eccentric compact binary coalescence throughout merger. We use this model to show that the gravitational-wave transients GW150914 and GW151226 can be effectively recovered with template banks of quasicircular, spin-aligned waveforms if the eccentricity e0 of these systems when they enter the aLIGO band at a gravitational-wave frequency of 14 Hz satisfies e0GW150914≤0.15 and e0GW151226≤0.1. We also find that varying the spin combinations of the quasicircular, spin-aligned template waveforms does not improve the recovery of nonspinning, eccentric signals when e0≥0.1. This suggests that these two signal manifolds are predominantly orthogonal. [ABSTRACT FROM AUTHOR]

We revisit the problem of computing the self-force on a scalar charge moving along an eccentric geodesic orbit around a Schwarzschild black hole. This work extends previous scalar self-force calculations for circular orbits, which were based on a regular "effective" point-particle source and a full 3D evolution code. We find good agreement between our results and previous calculations based on a (1+1) time-domain code. Finally, our data visualization is unconventional: we plot the self-force through full radial cycles to create "self-force loops," which reveal many interesting features that are less apparent in standard presentations of eccentric-orbit self-force data. [ABSTRACT FROM AUTHOR]