271 research outputs found

### Numerical simulations of compact object binaries

Coalescing compact object binaries consisting of black holes and/or Neutron
stars are a prime target for ground-based gravitational wave detectors. This
article reviews the status of numerical simulations of these systems, with an
emphasis on recent progress.Comment: Minor corrections, including typos and gramma

### Measuring neutron star tidal deformability with Advanced LIGO: a Bayesian analysis of neutron star - black hole binary observations

The discovery of gravitational waves (GW) by Advanced LIGO has ushered us
into an era of observational GW astrophysics. Compact binaries remain the
primary target sources for LIGO, of which neutron star-black hole (NSBH)
binaries form an important subset. GWs from NSBH sources carry signatures of
(a) the tidal distortion of the neutron star by its companion black hole during
inspiral, and (b) its potential tidal disruption near merger. In this paper, we
present a Bayesian study of the measurability of neutron star tidal
deformability $\Lambda_\mathrm{NS}\propto (R/M)^{5}$ using observation(s) of
inspiral-merger GW signals from disruptive NSBH coalescences, taking into
account the crucial effect of black hole spins. First, we find that if
non-tidal templates are used to estimate source parameters for an NSBH signal,
the bias introduced in the estimation of non-tidal physical parameters will
only be significant for loud signals with signal-to-noise ratios $> 30$. For
similarly loud signals, we also find that we can begin to put interesting
constraints on $\Lambda_\mathrm{NS}$ (factor of 1-2) with individual
observations. Next, we study how a population of realistic NSBH detections will
improve our measurement of neutron star tidal deformability. For astrophysical
populations of $disruptive$ NSBH mergers, we find 20-35 events to be sufficient
to constrain $\Lambda_\mathrm{NS}$ within $\pm 25-50\%$, depending on the
chosen equation of state. In this we also assume that LIGO will detect black
holes with masses within the astrophysical $mass$-$gap$. If the mass-gap
remains preserved in NSBHs detected by LIGO, we estimate that $25\%$
$additional$ detections will furnish comparable tidal measurement accuracy. In
both cases, we find that the loudest 5-10 events to provide most of the tidal
information, thereby facilitating targeted follow-ups of NSBHs in the upcoming
LIGO-Virgo runs.Comment: 21 pages, 17 figure

### Suitability of post-Newtonian/numerical-relativity hybrid waveforms for gravitational wave detectors

This article presents a study of the sufficient accuracy of post-Newtonian
and numerical relativity waveforms for the most demanding usage case: parameter
estimation of strong sources in advanced gravitational wave detectors. For
black hole binaries, these detectors require accurate waveform models which can
be constructed by fusing an analytical post-Newtonian inspiral waveform with a
numerical relativity merger-ringdown waveform. We perform a comprehensive
analysis of errors that enter such "hybrid waveforms". We find that the
post-Newtonian waveform must be aligned with the numerical relativity waveform
to exquisite accuracy, about 1/100 of a gravitational wave cycle. Phase errors
in the inspiral phase of the numerical relativity simulation must be controlled
to less than about 0.1rad. (These numbers apply to moderately optimistic
estimates about the number of GW sources; exceptionally strong signals require
even smaller errors.) The dominant source of error arises from the inaccuracy
of the investigated post-Newtonian Taylor-approximants. Using our error
criterium, even at 3.5-th post-Newtonian order, hybridization has to be
performed significantly before the start of the longest currently available
numerical waveforms which cover 30 gravitational wave cycles. The current
investigation is limited to the equal-mass, zero-spin case and does not take
into account calibration errors of the gravitational wave detectors.Comment: 32 pages, 12 figures, submitted to CQG for the NRDA2010 conference
proceedings, added new figure (fig. 5) since last versio

### Compact Binary Waveform Center-of-Mass Corrections

We present a detailed study of the center-of-mass (c.m.) motion seen in
simulations produced by the Simulating eXtreme Spacetimes (SXS) collaboration.
We investigate potential physical sources for the large c.m. motion in binary
black hole simulations and find that a significant fraction of the c.m. motion
cannot be explained physically, thus concluding that it is largely a gauge
effect. These large c.m. displacements cause mode mixing in the gravitational
waveform, most easily recognized as amplitude oscillations caused by the
dominant (2,$\pm$2) modes mixing into subdominant modes. This mixing does not
diminish with increasing distance from the source; it is present even in
asymptotic waveforms, regardless of the method of data extraction. We describe
the current c.m.-correction method used by the SXS collaboration, which is
based on counteracting the motion of the c.m. as measured by the trajectories
of the apparent horizons in the simulations, and investigate potential methods
to improve that correction to the waveform. We also present a complementary
method for computing an optimal c.m. correction or evaluating any other c.m.
transformation based solely on the asymptotic waveform data.Comment: 20 pages, 15 figure

### High accuracy simulations of black hole binaries:spins anti-aligned with the orbital angular momentum

High-accuracy binary black hole simulations are presented for black holes
with spins anti-aligned with the orbital angular momentum. The particular case
studied represents an equal-mass binary with spins of equal magnitude
S/m^2=0.43757 \pm 0.00001. The system has initial orbital eccentricity ~4e-5,
and is evolved through 10.6 orbits plus merger and ringdown. The remnant mass
and spin are M_f=(0.961109 \pm 0.000003)M and S_f/M_f^2=0.54781 \pm 0.00001,
respectively, where M is the mass during early inspiral. The gravitational
waveforms have accumulated numerical phase errors of <~ 0.1 radians without any
time or phase shifts, and <~ 0.01 radians when the waveforms are aligned with
suitable time and phase shifts. The waveform is extrapolated to infinity using
a procedure accurate to <~ 0.01 radians in phase, and the extrapolated waveform
differs by up to 0.13 radians in phase and about one percent in amplitude from
the waveform extracted at finite radius r=350M. The simulations employ
different choices for the constraint damping parameters in the wave zone; this
greatly reduces the effects of junk radiation, allowing the extraction of a
clean gravitational wave signal even very early in the simulation.Comment: 14 pages, 15 figure

### Numerical Relativity Injection Infrastructure

This document describes the new Numerical Relativity (NR) injection
infrastructure in the LIGO Algorithms Library (LAL), which henceforth allows
for the usage of NR waveforms as a discrete waveform approximant in LAL. With
this new interface, NR waveforms provided in the described format can directly
be used as simulated GW signals ("injections") for data analyses, which include
parameter estimation, searches, hardware injections etc. As opposed to the
previous infrastructure, this new interface natively handles sub-dominant modes
and waveforms from numerical simulations of precessing binary black holes,
making them directly accessible to LIGO analyses. To correctly handle
precessing simulations, the new NR injection infrastructure internally
transforms the NR data into the coordinate frame convention used in LAL.Comment: 20 pages, 2 figures, technical repor

### Stability of exact force-free electrodynamic solutions and scattering from spacetime curvature

Recently, a family of exact force-free electrodynamic (FFE) solutions was
given by Brennan, Gralla and Jacobson, which generalizes earlier solutions by
Michel, Menon and Dermer, and other authors. These solutions have been proposed
as useful models for describing the outer magnetosphere of conducting stars. As
with any exact analytical solution that aspires to describe actual physical
systems, it is vitally important that the solution possess the necessary
stability. In this paper, we show via fully nonlinear numerical simulations
that the aforementioned FFE solutions, despite being highly special in their
properties, are nonetheless stable under small perturbations. Through this
study, we also introduce a three-dimensional pseudospectral relativistic FFE
code that achieves exponential convergence for smooth test cases, as well as
two additional well-posed FFE evolution systems in the appendix that have
desirable mathematical properties. Furthermore, we provide an explicit analysis
that demonstrates how propagation along degenerate principal null directions of
the spacetime curvature tensor simplifies scattering, thereby providing an
intuitive understanding of why these exact solutions are tractable, i.e. why
they are not backscattered by spacetime curvature.Comment: 33 pages, 21 figures; V2 updated to match published versio

### Black hole initial data on hyperboloidal slices

We generalize Bowen-York black hole initial data to hyperboloidal constant
mean curvature slices which extend to future null infinity. We solve this
initial value problem numerically for several cases, including unequal mass
binary black holes with spins and boosts. The singularity at null infinity in
the Hamiltonian constraint associated with a constant mean curvature
hypersurface does not pose any particular difficulties. The inner boundaries of
our slices are minimal surfaces. Trumpet configurations are explored both
analytically and numerically.Comment: version for publication in Phys. Rev.

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