Bela Szilagyi

Simulations of Binary Black Hole Mergers Using Spectral Methods

Several improvements in numerical methods and gauge choice are presented that make it possible now to perform simulations of the merger and ringdown phases of ``generic binary black hole evolutions using the pseudospectral evolution code SpEC. These improvements include the use of a new damped-wave gauge condition, a new grid structure with appropriate filtering that improves stability, and better adaptivity in conforming the grid structures to the shapes and sizes of the black holes. Simulations illustrating the success of these new methods are presented for a variety of binary black hole systems. These include fairly generic systems with unequal masses (up to

Error-analysis and comparison to analytical models of numerical waveforms produced by the NRAR Collaboration

2ensuremath{mathbin:}1

Unambiguous determination of gravitational waveforms from binary black hole mergers.

mass ratios), and spins (with magnitudes up to

The NINJA-2 catalog of hybrid post-Newtonian/numerical-relativity waveforms for non-precessing black-hole binaries

0.4{M}^{2}

Simulating merging binary black holes with nearly extremal spins

) pointing in various directions.

BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

The Numerical–Relativity–Analytical–Relativity (NRAR) collaboration is a joint effort between members of the numerical relativity, analytical relativity and gravitational-wave data analysis communities. The goal of the NRAR collaboration is to produce numerical-relativity simulations of compact binaries and use them to develop accurate analytical templates for the LIGO/Virgo Collaboration to use in detecting gravitational-wave signals and extracting astrophysical information from them. We describe the results of the first stage of the NRAR project, which focused on producing an initial set of numerical waveforms from binary black holes with moderate mass ratios and spins, as well as one non-spinning binary configuration which has a mass ratio of 10. All of the numerical waveforms are analysed in a uniform and consistent manner, with numerical errors evaluated using an analysis code created by members of the NRAR collaboration. We compare previously-calibrated, non-precessing analytical waveforms, notably the effective-one-body (EOB) and phenomenological template families, to the newly-produced numerical waveforms. We find that when the binarys total mass is ~100–200M⊙, current EOB and phenomenological models of spinning, non-precessing binary waveforms have overlaps above 99% (for advanced LIGO) with all of the non-precessing-binary numerical waveforms with mass ratios ≤4, when maximizing over binary parameters. This implies that the loss of event rate due to modelling error is below 3%. Moreover, the non-spinning EOB waveforms previously calibrated to five non-spinning waveforms with mass ratio smaller than 6 have overlaps above 99.7% with the numerical waveform with a mass ratio of 10, without even maximizing on the binary parameters.

High-accuracy gravitational waveforms for binary black hole mergers with nearly extremal spins

Gravitational radiation is properly defined only at future null infinity (J+), but in practice it is estimated from data calculated at a finite radius. We have used characteristic extraction to calculate gravitational radiation at J+ for the inspiral and merger of two equal-mass nonspinning black holes. Thus we have determined the first unambiguous merger waveforms for this problem. The implementation is general purpose and can be applied to calculate the gravitational radiation, at J+, given data at a finite radius calculated in another computation.

Characteristic extraction tool for gravitational waveforms

The numerical injection analysis (NINJA) project is a collaborative effort between members of the numerical-relativity and gravitational wave data-analysis communities. The purpose of NINJA is to study the sensitivity of existing gravitational-wave search and parameter-estimation algorithms using numerically generated waveforms and to foster closer collaboration between the numerical-relativity and data-analysis communities. The first NINJA project used only a small number of injections of short numerical-relativity waveforms, which limited its ability to draw quantitative conclusions. The goal of the NINJA-2 project is to overcome these limitations with long post-Newtonian—numerical-relativity hybrid waveforms, large numbers of injections and the use of real detector data. We report on the submission requirements for the NINJA-2 project and the construction of the waveform catalog. Eight numerical-relativity groups have contributed 56 hybrid waveforms consisting of a numerical portion modeling the late inspiral, merger and ringdown stitched to a post-Newtonian portion modeling the early inspiral. We summarize the techniques used by each group in constructing their submissions. We also report on the procedures used to validate these submissions, including examination in the time and frequency domains and comparisons of waveforms from different groups against each other. These procedures have so far considered only the (l, m) = (2, 2) mode. Based on these studies, we judge that the hybrid waveforms are suitable for NINJA-2 studies. We note some of the plans for these investigations.

Effects of neutron-star dynamic tides on gravitational waveforms within the effective-one-body approach

Astrophysically realistic black holes may have spins that are nearly extremal (i.e., close to 1 in ndimensionless units). Numerical simulations of binary black holes are important tools both for calibrating nanalytical templates for gravitational-wave detection and for exploring the nonlinear dynamics of curved nspacetime. However, all previous simulations of binary-black-hole inspiral, merger, and ringdown have nbeen limited by an apparently insurmountable barrier: the merging holes’ spins could not exceed 0.93, nwhich is still a long way from the maximum possible value in terms of the physical effects of the spin. In nthis paper, we surpass this limit for the first time, opening the way to explore numerically the behavior of nmerging, nearly extremal black holes. Specifically, using an improved initial-data method suitable for nbinary black holes with nearly extremal spins, we simulate the inspiral (through 12.5 orbits), merger and nringdown of two equal-mass black holes with equal spins of magnitude 0.95 antialigned with the orbital nangular momentum.

Dynamical excision boundaries in spectral evolutions of binary black hole spacetimes

Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron star mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state (EOS) and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 M_☉ neutron star, 5.6 M_☉ black hole), high-spin (black hole J/M^2 = 0.9) system with the K_0 = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M_☉ of nuclear matter is ejected from the system, while another 0.3 M_☉ forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Ye of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ~ 6 MeV) and luminous in neutrinos (L_ν ~ 10^54 erg s^–1), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution.